FEATURES FUNCTIONAL BLOCK DIAGRAM AVDD Low power: 55 mW per channel at 65 MSPS with scalable power options SNR = 75.5 dB (to Nyquist) SFDR = 91.6 dBc (to Nyquist) DNL = ±0.6 LSB (typical), INL = ±1.1 LSB (typical) Serial LVDS (ANSI-644, default) Low power, reduced signal option (similar to IEEE 1596.3) Data and frame clock outputs 650 MHz full power analog bandwidth 2 V p-p input voltage range 1.8 V supply operation Serial port control Full chip and individual channel power-down modes Flexible bit orientation Built-in and custom digital test pattern generation Programmable clock and data alignment Programmable output resolution Standby mode PDWN AD9257 DRVDD 14 VIN+ A VIN– A ADC VIN+ B VIN– B ADC VIN+ C VIN– C ADC VIN+ D VIN– D ADC VIN+ E VIN– E ADC VIN+ F VIN– F ADC VIN+ G VIN– G ADC VIN+ H VIN– H ADC D+ A D– A SERIAL LVDS 14 D+ B D– B SERIAL LVDS 14 D+ C D– C SERIAL LVDS 14 D+ D D– D SERIAL LVDS 14 D+ E D– E SERIAL LVDS 14 D+ F D– F SERIAL LVDS 14 D+ G D– G SERIAL LVDS 14 APPLICATIONS D+ H D– H SERIAL LVDS VREF SENSE Medical imaging and nondestructive ultrasound Portable ultrasound and digital beam-forming systems Quadrature radio receivers Diversity radio receivers Optical networking Test equipment VCM 1.0V REF SELECT SERIAL PORT INTERFACE DATA RATE MULTIPLIER SYNC RBIAS AGND CSB SDIO/ SCLK/ DFS DTP CLK+ CLK– FCO+ FCO– DCO+ DCO– 10206-001 Data Sheet Octal, 14-Bit, 40/65 MSPS, Serial LVDS, 1.8 V Analog-to-Digital Converter AD9257 Figure 1. GENERAL DESCRIPTION The AD9257 is an octal, 14-bit, 40 MSPS and 65 MSPS analogto-digital converter (ADC) with an on-chip sample-and-hold circuit designed for low cost, low power, small size, and ease of use. The product operates at a conversion rate of up to 65 MSPS and is optimized for outstanding dynamic performance and low power in applications where a small package size is critical. The ADC requires a single 1.8 V power supply and LVPECL-/ CMOS-/LVDS-compatible sample rate clock for full performance operation. No external reference or driver components are required for many applications. The ADC automatically multiplies the sample rate clock for the appropriate LVDS serial data rate. A data clock output (DCO) for capturing data on the output and a frame clock output (FCO) for signaling a new output byte are provided. Individual channel power-down is supported and typically consumes less than 2 mW when all channels are disabled. The ADC contains several features designed to maximize flexibility and minimize system cost, such as programmable clock and data Rev. A alignment and programmable digital test pattern generation. The available digital test patterns include built-in deterministic and pseudorandom patterns, along with custom user-defined test patterns entered via the serial port interface (SPI). The AD9257 is available in an RoHS-compliant, 64-lead LFCSP. It is specified over the industrial temperature range of −40°C to +85°C. This product is protected by a U.S. patent. PRODUCT HIGHLIGHTS 1. 2. 3. 4. 5. Small Footprint. Eight ADCs are contained in a small, space-saving package. Low Power of 55 mW/Channel at 65 MSPS with Scalable Power Options. Ease of Use. A data clock output (DCO) is provided that operates at frequencies of up to 455 MHz and supports double data rate (DDR) operation. User Flexibility. The SPI control offers a wide range of flexible features to meet specific system requirements. Pin Compatible with the AD9637 (12-Bit Octal ADC). Document Feedback Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 ©2011–2013 Analog Devices, Inc. All rights reserved. Technical Support www.analog.com AD9257 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Power Dissipation and Power-Down Mode ........................... 22 Applications ....................................................................................... 1 Digital Outputs and Timing ..................................................... 23 General Description ......................................................................... 1 Built-In Output Test Modes .......................................................... 27 Functional Block Diagram .............................................................. 1 Output Test Modes ..................................................................... 27 Product Highlights ........................................................................... 1 Serial Port Interface (SPI) .............................................................. 28 Revision History ............................................................................... 2 Configuration Using the SPI ..................................................... 28 Specifications..................................................................................... 3 Hardware Interface..................................................................... 29 DC Specifications ......................................................................... 3 Configuration Without the SPI ................................................ 29 AC Specifications.......................................................................... 4 SPI Accessible Features .............................................................. 29 Digital Specifications ................................................................... 5 Memory Map .................................................................................. 30 Switching Specifications .............................................................. 6 Reading the Memory Map Register Table............................... 30 Timing Specifications .................................................................. 6 Memory Map Register Table ..................................................... 31 Absolute Maximum Ratings............................................................ 8 Memory Map Register Descriptions ........................................ 34 Thermal Characteristics .............................................................. 8 Applications Information .............................................................. 36 ESD Caution .................................................................................. 8 Design Guidelines ...................................................................... 36 Pin Configuration and Function Descriptions ............................. 9 Power and Ground Recommendations ................................... 36 Typical Performance Characteristics ........................................... 11 Clock Stability Considerations ................................................. 36 AD9257-65 .................................................................................. 11 Exposed Pad Thermal Heat Slug Recommendations ............ 36 AD9257-40 .................................................................................. 14 VCM ............................................................................................. 36 Equivalent Circuits ......................................................................... 17 Reference Decoupling ................................................................ 36 Theory of Operation ...................................................................... 18 SPI Port ........................................................................................ 36 Analog Input Considerations.................................................... 18 Outline Dimensions ....................................................................... 37 Voltage Reference ....................................................................... 19 Ordering Guide .......................................................................... 37 Clock Input Considerations ...................................................... 20 REVISION HISTORY 10/11—Revision 0: Initial Version 4/13—Rev. 0 to Rev. A Changes to Table 1 ............................................................................ 3 Changes to AC Specifications Section ........................................... 4 Added Propagation Delay of 1.5 ns Min and 3.1 ns Max; Table 4 .. 6 Added CLK Divider = 8 to Figure 7, Figure 9, Figure 10, and Figure 11 Captions.......................................................................... 11 Changes to Figure 14 and Figure 17 ............................................. 12 Added CLK Divider = 8 to Figure 22, Figure 24, and Figure 25 Captions ........................................................................................... 14 Added CLK Divider = 4 to Figure 28 and Figure 31; Changes to Figure 32 .......................................................................................... 15 Changes to Figure 36 and Figure 37 ............................................. 17 Changes to Figure 56 ...................................................................... 22 Changes to Digital Outputs and Timing Section ....................... 23 Changes to Channel Specific Registers Section .......................... 30 Changes to Register 0x21, Bit 3; Table 17 .................................... 33 Changes to Bits[6:4]—Input Clock Phase Adjust Section......... 35 Added Clock Stability Considerations Section ........................... 36 Updated Outline Dimensions ....................................................... 37 Rev. A | Page 2 of 40 Data Sheet AD9257 SPECIFICATIONS DC SPECIFICATIONS AVDD = 1.8 V, DRVDD = 1.8 V, 2 V p-p differential input, 1.0 V internal reference, AIN = −1.0 dBFS, unless otherwise noted. Table 1. Parameter 1 RESOLUTION ACCURACY No Missing Codes Offset Error Offset Matching Gain Error Gain Matching Differential Nonlinearity (DNL) Integral Nonlinearity (INL) TEMPERATURE DRIFT Offset Error INTERNAL VOLTAGE REFERENCE Output Voltage (1 V Mode) Load Regulation at 1.0 mA (VREF = 1 V) Input Resistance INPUT-REFERRED NOISE VREF = 1.0 V ANALOG INPUTS Differential Input Voltage (VREF = 1 V) Common-Mode Voltage Common-Mode Range Differential Input Resistance Differential Input Capacitance POWER SUPPLY AVDD DRVDD IAVDD IDRVDD (ANSI-644 Mode) IDRVDD (Reduced Range Mode) TOTAL POWER CONSUMPTION Total Power Dissipation (Eight Channels, ANSI-644 Mode) Total Power Dissipation (Eight Channels, Reduced Range Mode) Power-Down Dissipation Standby Dissipation 2 1 2 Temp Full Full Full Full Full Full Full Min 14 −0.6 0 −6.0 −1.0 −1.0 −3.1 Full Full Full Full AD9257-40 Typ Max Guaranteed −0.3 0.2 −2.1 +1.7 −0.5/+0.8 ±1.1 +0.1 0.6 2.0 +5.0 +1.7 +3.1 Min 14 −0.7 0 −6.0 −1.0 −1.0 −4.0 ±2 0.98 0.99 2 7.5 AD9257-65 Typ Max Guaranteed −0.3 +0.1 0.23 0.6 −2.9 +1.0 +1.6 +5.0 ±0.6 +1.6 ±1.1 +4.0 ±2 1.01 0.98 0.99 2 7.5 Unit Bits % FSR % FSR % FSR % FSR LSB LSB ppm/°C 1.01 V mV kΩ 25°C 0.91 0.94 LSB rms Full Full Full 2 0.9 2 0.9 V p-p V V kΩ pF 0.5 Full Full Full Full Full 25°C 1.3 0.5 5.2 3.5 1.7 1.7 1.3 5.2 3.5 1.8 1.8 147 53 38 1.9 1.9 156 85 1.7 1.7 1.8 1.8 198 60 45 1.9 1.9 211 93 V V mA mA mA Full 360 434 464 547 mW 25°C 333 437 mW 25°C 25°C 1 74 1 92 mW mW See the AN-835 Application Note, Understanding High Speed ADC Testing and Evaluation, for definitions and for details on how these tests were completed. Can be controlled via the SPI. Rev. A | Page 3 of 40 AD9257 Data Sheet AC SPECIFICATIONS AVDD = 1.8 V, DRVDD = 1.8 V, 2 V p-p differential input, 1.0 V internal reference, AIN = −1.0 dBFS, unless otherwise noted. CLK divider = 8 used for typical characteristics at input frequency ≥ 19.7 MHz. Table 2. Parameter 1 SIGNAL-TO-NOISE RATIO (SNR) fIN = 9.7 MHz fIN = 19.7 MHz fIN = 30.5 MHz fIN = 63.5 MHz fIN = 69.5 MHz fIN = 123.4 MHz SIGNAL-TO-NOISE AND DISTORTION RATIO (SINAD) fIN = 9.7 MHz fIN = 19.7 MHz fIN = 30.5 MHz fIN = 63.5 MHz fIN = 69.5 MHz fIN = 123.4 MHz EFFECTIVE NUMBER OF BITS (ENOB) fIN = 9.7 MHz fIN = 19.7 MHz fIN = 30.5 MHz fIN = 63.5 MHz fIN = 69.5 MHz fIN = 123.4 MHz SPURIOUS-FREE DYNAMIC RANGE (SFDR) fIN = 9.7 MHz fIN = 19.7 MHz fIN = 30.5 MHz fIN = 63.5 MHz fIN = 69.5 MHz fIN = 123.4 MHz WORST HARMONIC (SECOND OR THIRD) fIN = 9.7 MHz fIN = 19.7 MHz fIN = 30.5 MHz fIN = 63.5 MHz fIN = 69.5 MHz fIN = 123.4 MHz WORST OTHER (EXCLUDING SECOND OR THIRD) fIN = 9.7 MHz fIN = 19.7 MHz fIN = 30.5 MHz fIN = 63.5 MHz fIN = 69.5 MHz fIN = 123.4 MHz TWO-TONE INTERMODULATION DISTORTION (IMD)—AIN1 AND AIN2 = −7.0 dBFS fIN1 = 8 MHz, fIN2 = 10 MHz fIN1 = 30 MHz, fIN2 = 32 MHz Temp 25°C Full 25°C 25°C 25°C 25°C 25°C Full 25°C 25°C 25°C 25°C 25°C Full 25°C 25°C 25°C 25°C 25°C Full 25°C 25°C 25°C 25°C Min 73.5 AD9257-40 Typ Max 75.9 75.8 75.7 Min 73.3 AD9257-65 Typ Max 75.7 75.6 75.5 74.9 dBFS dBFS dBFS dBFS dBFS dBFS 74.7 73.2 72.5 75.8 75.7 75.6 72.0 75.6 75.6 75.4 74.8 dBFS dBFS dBFS dBFS dBFS dBFS 74.5 72.8 11.7 12.3 12.3 12.3 11.7 12.3 12.3 12.2 12.1 Bits Bits Bits Bits Bits Bits 12.1 11.8 80 25°C Full 25°C 25°C 25°C 25°C 96 96 97 96 96 91 95 dBc dBc dBc dBc dBc dBc 87 83 −99 −96 −100 −80 −99 −98 −91 −98 −79 −87 −83 25°C Full 25°C 25°C 25°C 25°C −96 −99 −97 25°C 25°C 95 Rev. A | Page 4 of 40 79 −86 −96 −96 −98 −95 Unit dBc dBc dBc dBc dBc dBc −94 dBc dBc dBc dBc dBc dBc 92 dBc dBc −98 −88 Data Sheet Parameter 1 CROSSTALK 2 Crosstalk (Overrange Condition) 3 POWER SUPPLY REJECTION RATIO (PSRR) 4 AVDD DRVDD ANALOG INPUT BANDWIDTH, FULL POWER AD9257 Temp 25°C 25°C 25°C Min AD9257-40 Typ Max −100 −92 Min AD9257-65 Typ Max −98 −94 52 73 650 25°C 52 71 650 Unit dB dB dB dB MHz See the AN-835 Application Note, Understanding High Speed ADC Testing and Evaluation, for definitions and for details on how these tests were completed. Crosstalk is measured at 10 MHz with −1.0 dBFS analog input on one channel and no input on the adjacent channel. 3 Overrange condition is 3 dB above the full-scale input range. 4 PSRR is measured by injecting a sinusoidal signal at 10 MHz to the power supply pin and measuring the output spur on the FFT. PSRR is calculated as the ratio of the amplitudes of the spur voltage over the pin voltage, expressed in decibels. 1 2 DIGITAL SPECIFICATIONS AVDD = 1.8 V, DRVDD = 1.8 V, 2 V p-p differential input, 1.0 V internal reference, AIN = −1.0 dBFS, unless otherwise noted. Table 3. Parameter 1 CLOCK INPUTS (CLK+, CLK−) Logic Compliance Differential Input Voltage 2 Input Voltage Range Input Common-Mode Voltage Input Resistance (Differential) Input Capacitance LOGIC INPUTS (PDWN, SYNC, SCLK) Logic 1 Voltage Logic 0 Voltage Input Resistance Input Capacitance LOGIC INPUT (CSB) Logic 1 Voltage Logic 0 Voltage Input Resistance Input Capacitance LOGIC INPUT (SDIO) Logic 1 Voltage Logic 0 Voltage Input Resistance Input Capacitance LOGIC OUTPUT (SDIO) 3 Logic 1 Voltage (IOH = 800 μA) Logic 0 Voltage (IOL = 50 μA) DIGITAL OUTPUTS (D± x), ANSI-644 Logic Compliance Differential Output Voltage (VOD) Output Offset Voltage (VOS) Output Coding (Default) DIGITAL OUTPUTS (D± x), LOW POWER, REDUCED SIGNAL OPTION Logic Compliance Differential Output Voltage (VOD) Output Offset Voltage (VOS) Output Coding (Default) Temp Min Full Full Full 25°C 25°C 0.2 AGND − 0.2 Full Full 25°C 25°C 1.2 0 Full Full 25°C 25°C 1.2 0 Full Full 25°C 25°C 1.2 0 Typ Max Unit 3.6 AVDD + 0.2 V p-p V V kΩ pF AVDD + 0.2 0.8 V V kΩ pF AVDD + 0.2 0.8 V V kΩ pF AVDD + 0.2 0.8 V V kΩ pF CMOS/LVDS/LVPECL 0.9 15 4 30 2 26 2 26 5 Full Full 1.79 0.05 V V Full Full 247 1.13 LVDS 350 1.21 Twos complement 454 1.38 mV V Full Full 150 1.13 LVDS 200 1.21 Twos complement 250 1.38 mV V See the AN-835 Application Note, Understanding High Speed ADC Testing and Evaluation, for definitions and for details on how these tests were completed. This is specified for LVDS and LVPECL only. 3 This is specified for 13 SDIO/DFS pins sharing the same connection. 1 2 Rev. A | Page 5 of 40 AD9257 Data Sheet SWITCHING SPECIFICATIONS AVDD = 1.8 V, DRVDD = 1.8 V, 2 V p-p differential input, 1.0 V internal reference, AIN = −1.0 dBFS, unless otherwise noted. Table 4. Parameter 1, 2 CLOCK 3 Input Clock Rate Conversion Rate Clock Pulse Width High (tEH) Clock Pulse Width Low (tEL) OUTPUT PARAMETERS3 Propagation Delay (tPD) Rise Time (tR) (20% to 80%) Fall Time (tF) (20% to 80%) FCO Propagation Delay (tFCO) DCO Propagation Delay (tCPD) 4 DCO to Data Delay (tDATA)4 DCO to FCO Delay (tFRAME)4 Data to Data Skew (tDATA-MAX − tDATA-MIN) Wake-Up Time (Standby) Wake-Up Time (Power-Down) 5 Pipeline Latency APERTURE Aperture Delay (tA) Aperture Uncertainty (Jitter) Out-of-Range Recovery Time Temp Min Full Full Full Full 10 10 Full Full Full Full Full Full Full Full 1.5 Typ Max Unit 520 40/65 MHz MSPS ns ns 3.1 ns ps ps ns ns ps ps ps 12.5/7.69 12.5/7.69 1.5 (tSAMPLE/28) − 300 (tSAMPLE/28) − 300 2.3 300 300 2.3 tFCO + (tSAMPLE/28) (tSAMPLE/28) (tSAMPLE/28) ±50 3.1 (tSAMPLE/28) + 300 (tSAMPLE/28) + 300 ±200 25°C 25°C Full 35 375 16 μs μs Clock cycles 25°C 25°C 25°C 1 0.1 1 ns ps rms Clock cycles See the AN-835 Application Note, Understanding High Speed ADC Testing and Evaluation, for definitions and for details on how these tests were completed. Measured on standard FR-4 material. 3 Can be adjusted via the SPI. 4 tSAMPLE/28 is based on the number of bits divided by 2 because the delays are based on half duty cycles. tSAMPLE = 1/fS. 5 Wake-up time is defined as the time required to return to normal operation from power-down mode. 1 2 TIMING SPECIFICATIONS Table 5. Parameter SYNC TIMING REQUIREMENTS tSSYNC tHSYNC SPI TIMING REQUIREMENTS tDS tDH tCLK tS tH tHIGH tLOW tEN_SDIO tDIS_SDIO Description Limit Unit SYNC to rising edge of CLK+ setup time SYNC to rising edge of CLK+ hold time See Figure 61 Setup time between the data and the rising edge of SCLK Hold time between the data and the rising edge of SCLK Period of the SCLK Setup time between CSB and SCLK Hold time between CSB and SCLK SCLK pulse width high SCLK pulse width low Time required for the SDIO pin to switch from an input to an output relative to the SCLK falling edge (not shown in Figure 61) Time required for the SDIO pin to switch from an output to an input relative to the SCLK rising edge (not shown in Figure 61) 0.24 0.40 ns typ ns typ 2 2 40 2 2 10 10 10 ns min ns min ns min ns min ns min ns min ns min ns min 10 ns min Rev. A | Page 6 of 40 Data Sheet AD9257 Timing Diagrams N–1 VIN± x tA N tEH tEL CLK– CLK+ tCPD DCO– DCO+ tFCO tFRAME FCO– FCO+ tPD tDATA MSB D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 MSB D12 N – 17 N – 17 N – 17 N – 17 N – 17 N – 17 N – 17 N – 17 N – 17 N – 17 N – 17 N – 17 N – 17 N – 17 N – 16 N – 16 D+ x 10206-002 D– x Figure 2. Word-Wise DDR,1× Frame, 14-Bit Output Mode (Default) N–1 VIN± x tA N tEH tEL CLK– CLK+ tCPD DCO– DCO+ tFRAME tFCO FCO– FCO+ tPD tDATA MSB N – 17 D10 N – 17 D9 N – 17 D8 N – 17 D7 N – 17 D6 N – 17 D5 N – 17 D4 N – 17 D3 N – 17 D2 N – 17 D+ x Figure 3. Word-Wise DDR, 1× Frame, 12-Bit Output Mode CLK+ tHSYNC 10206-004 tSSYNC SYNC Figure 4. SYNC Input Timing Requirements Rev. A | Page 7 of 40 D1 N – 17 D0 N – 17 MSB N – 16 D10 N – 16 10206-003 D– x AD9257 Data Sheet ABSOLUTE MAXIMUM RATINGS THERMAL CHARACTERISTICS Table 6. Parameter Electrical AVDD to AGND DRVDD to AGND Digital Outputs (D± x, DCO+, DCO−, FCO+, FCO−) to AGND CLK+, CLK− to AGND VIN+ x, VIN− x to AGND SCLK/DTP, SDIO/DFS, CSB to AGND SYNC, PDWN to AGND RBIAS to AGND VREF, SENSE to AGND Environmental Operating Temperature Range (Ambient) Maximum Junction Temperature Lead Temperature (Soldering, 10 sec) Storage Temperature Range (Ambient) Rating −0.3 V to +2.0 V −0.3 V to +2.0 V −0.3 V to +2.0 V The exposed paddle must be soldered to the ground plane for the LFCSP package. Soldering the exposed paddle to the PCB increases the reliability of the solder joints and maximizes the thermal capability of the package. Table 7. Thermal Resistance Airflow Velocity (m/sec) 0 1.0 2.5 θJA1, 2 22.3 19.5 17.5 θJC1, 3 1.4 N/A N/A θJB1, 4 N/A 11.8 N/A ΨJT1, 2 0.1 0.2 0.2 −0.3 V to +2.0 V −0.3 V to +2.0 V −0.3 V to +2.0 V −0.3 V to +2.0 V −0.3 V to +2.0 V −0.3 V to +2.0 V Package Type 64-Lead LFCSP 9 mm × 9 mm (CP-64-4) −40°C to +85°C 150°C 300°C −65°C to +150°C Typical θJA is specified for a 4-layer PCB with a solid ground plane. As shown Table 7, airflow improves heat dissipation, which reduces θJA. In addition, metal in direct contact with the package leads from metal traces, through holes, ground, and power planes reduces θJA. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Unit °C/W °C/W °C/W Per JEDEC 51-7, plus JEDEC 25-5 2S2P test board. Per JEDEC JESD51-2 (still air) or JEDEC JESD51-6 (moving air). Per MIL-Std 883, Method 1012.1. 4 Per JEDEC JESD51-8 (still air). 1 2 3 ESD CAUTION Rev. A | Page 8 of 40 Data Sheet AD9257 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 VIN+ F VIN– F AVDD VIN– E VIN+ E AVDD SYNC VCM VREF SENSE RBIAS VIN+ D VIN– D AVDD VIN– C VIN+ C PIN CONFIGURATION AND FUNCTION DESCRIPTIONS PIN 1 INDICATOR 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 AD9257 TOP VIEW (Not to Scale) 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 AVDD VIN+ B VIN– B AVDD VIN– A VIN+ A AVDD PDWN CSB SDIO/DFS SCLK/DTP AVDD DNC DRVDD D+ A D– A NOTES 1. DNC = DO NOT CONNECT. DO NOT CONNECT TO THIS PIN. 2. THE EXPOSED PAD MUST BE CONNECTED TO ANALOG GROUND. 10206-005 D– G D+ G D– F D+ F D– E D+ E DCO– DCO+ FCO– FCO+ D– D D+ D D– C D+ C D– B D+ B 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 AVDD VIN+ G VIN– G AVDD VIN– H VIN+ H AVDD AVDD CLK– CLK+ AVDD AVDD DNC DRVDD D– H D+ H Figure 5. Pin Configuration, Top View Table 8. Pin Function Descriptions Pin No. 0, EP Mnemonic AGND, Exposed Pad 1, 4, 7, 8, 11, 12, 37, 42, 45, 48, 51, 59, 62 13, 36 14, 35 2, 3 5, 6 9, 10 15, 16 17, 18 19, 20 21, 22 23, 24 25, 26 27, 28 29, 30 31, 32 33, 34 38 39 40 41 43, 44 46, 47 49, 50 52, 53 AVDD Description Analog Ground, Exposed Pad. The exposed thermal pad on the bottom of the package provides the analog ground for the part. This exposed pad must be connected to ground for proper operation. 1.8 V Analog Supply. DNC DRVDD VIN+ G, VIN− G VIN− H, VIN+ H CLK−, CLK+ D− H, D+ H D− G, D+ G D− F, D+ F D− E, D+ E DCO−, DCO+ FCO−, FCO+ D− D, D+ D D− C, D+ C D− B, D + B D− A, D+ A SCLK/DTP SDIO/DFS CSB PDWN VIN+ A, VIN− A VIN− B, VIN+ B VIN+ C, VIN− C VIN− D, VIN+ D Do Not Connect. 1.8 V Digital Output Driver Supply. ADC G Analog Input True, ADC G Analog Input Complement. ADC H Analog Input Complement, ADC H Analog Input True. Input Clock Complement, Input Clock True. ADC H Digital Output Complement, ADC H Digital Output True. ADC G Digital Output Complement, ADC G Digital Output True. ADC F Digital Output Complement, ADC F Digital Output True. ADC E Digital Output Complement, ADC E Digital Output True. Data Clock Digital Output Complement, Data Clock Digital Output True. Frame Clock Digital Output Complement, Frame Clock Digital Output True. ADC D Digital Output Complement, ADC D Digital Output True. ADC C Digital Output Complement, ADC C Digital Output True. ADC B Digital Output Complement, ADC B Digital Output True. ADC A Digital Output Complement, ADC A Digital Output True. Serial Clock (SCLK)/Digital Test Pattern (DTP). Serial Data Input/Output (SDIO)/Data Format Select (DFS). Chip Select Bar. Power-Down. ADC A Analog Input True, ADC A Analog Input Complement. ADC B Analog Input Complement, ADC B Analog Input True. ADC C Analog Input True, ADC C Analog Input Complement. ADC D Analog Input Complement, ADC D Analog Input True. Rev. A | Page 9 of 40 AD9257 Pin No. 54 55 56 57 58 60, 61 63, 64 Data Sheet Mnemonic RBIAS SENSE VREF VCM SYNC VIN+ E, VIN− E VIN− F, VIN+ F Description Sets analog current bias. Connect to 10 kΩ (1% tolerance) resistor to ground. Reference Mode Selection. Voltage Reference Input/Output. Analog Output Voltage at Midsupply. Sets common mode of the analog inputs. Digital Input. SYNC input to clock divider. 30 kΩ internal pull-down. ADC E Analog Input True, ADC E Analog Input Complement. ADC F Analog Input Complement, ADC F Analog Input True. Rev. A | Page 10 of 40 Data Sheet AD9257 TYPICAL PERFORMANCE CHARACTERISTICS AD9257-65 0 65MSPS 9.7MHz AT –1dBFS SNR = 74.7dB (75.7dBFS) SFDR = 93.5dBc –15 –30 AMPLITUDE (dBFS) –45 –60 –75 –90 –75 –90 –120 –120 9 12 15 18 21 24 27 30 –135 10206-006 6 FREQUENCY (MHz) 3 9 12 15 18 21 24 27 30 Figure 9. Single-Tone 16k FFT with fIN = 19.7 MHz, fSAMPLE = 65 MSPS, CLK Divider = 8 0 65MSPS 63.5MHz AT –1dBFS SNR = 73.9dB (74.9dBFS) SFDR = 95.4dBc –15 –30 AMPLITUDE (dBFS) –30 –15 –45 –60 –75 –90 –45 –60 –75 –90 –105 –105 –120 –120 3 6 9 12 15 18 21 24 27 30 FREQUENCY (MHz) –135 10206-007 –135 3 0 –15 –30 –30 AMPLITUDE (dBFS) 0 –75 2F2 + F1 –90 2F2 – F1 2F1 + F2 2F1 – F2 F2 – F1 F1 + F2 9 12 15 18 21 24 27 30 Figure 10. Single-Tone 16k FFT with fIN = 30.5 MHz, fSAMPLE = 65 MSPS, CLK Divider = 8 –15 –60 6 FREQUENCY (MHz) Figure 7. Single-Tone 16k FFT with fIN = 63.5 MHz, fSAMPLE = 65 MSPS, CLK Divider = 8 –45 65MSPS 30.5MHz AT –1dBFS SNR = 74.7dB (75.7dBFS) SFDR = 96.7dBc 10206-109 0 –105 6 FREQUENCY (MHz) Figure 6. Single-Tone 16k FFT with fIN = 9.7 MHz, fSAMPLE = 65 MSPS AMPLITUDE (dBFS) –60 –105 3 AMPLITUDE (dBFS) –45 –105 –135 65MSPS 19.7MHz AT –1dBFS SNR = 74.7dB (75.7dBFS) SFDR = 96.7dBc 65MSPS 123.4MHz AT –1dBFS SNR = 72.2dB (73.2dBFS) SFDR = 83.0dBc –45 –60 –75 –90 –105 –120 –120 3 6 9 12 15 18 21 24 27 30 FREQUENCY (MHz) Figure 8. Two-Tone 16k FFT with fIN1 = 30 MHz and fIN2 = 32 MHz, fSAMPLE = 65 MSPS –135 10206-008 –135 3 6 9 12 15 18 21 FREQUENCY (MHz) 24 27 30 10206-010 AMPLITUDE (dBFS) –30 –15 10206-009 0 Figure 11. Single-Tone 16k FFT with fIN = 123.4 MHz, fSAMPLE = 65 MSPS, CLK Divider = 8 Rev. A | Page 11 of 40 AD9257 Data Sheet 0 105 –20 100 SNR/SFDR (dBFS/dBc) SFDR/IMD3 (dBc/dBFS) SFDR (dBc) SFDR (dBc) –40 IMD3 (dBc) –60 –80 SFDR (dBFS) 95 90 85 80 SNR (dBFS) –100 75 –66 –54 –42 –30 –18 70 –40 10206-011 –78 –6 INPUT AMPLITUDE (dBFS) Figure 12. Two-Tone SFDR/IMD3 vs. Input Amplitude (AIN) with fIN1 = 30 MHz and fIN2 = 32 MHz, fSAMPLE = 65 MSPS –15 35 85 60 Figure 15. SNR/SFDR vs. Temperature, fIN = 9.7 MHz, fSAMPLE = 65 MSPS 110 120 SFDR (dBc) 100 SFDRFS 100 90 SNR/SFDR (dBFS/dBc) SNR/SFDR (dBFS/dBc) 10 TEMPERATURE (°C) 10206-014 IMD3 (dBFS) –120 –90 SNRFS 80 60 SFDR 40 SNR 80 SNR (dBFS) 70 60 50 40 30 20 20 –70 –60 –50 –40 –30 –20 –10 0 INPUT AMPLITUDE (dBFS) 0 10206-012 –80 0 40 60 100 120 140 160 180 200 60 65 Figure 16. SNR/SFDR vs. fIN, fSAMPLE = 65 MSPS 105 105 100 100 SNR/SFDR (dBFS/dBc) SFDR 95 90 85 80 SFDR 95 90 85 80 SNRFS SNRFS 30 35 40 45 50 55 60 65 SAMPLE FREQUENCY (MSPS) 10206-013 25 70 20 25 30 35 40 45 50 55 SAMPLE FREQUENCY (MSPS) Figure 17. SNR/SFDR vs. Encode, fIN = 30.5 MHz, CLK Divider = 4 Figure 14. SNR/SFDR vs. Encode, fIN = 19.7 MHz, CLK Divider = 4 Rev. A | Page 12 of 40 10206-016 75 75 70 20 80 INPUT FREQUENCY (MHz) Figure 13. SNR/SFDR vs. Analog Input Level, fIN = 9.7 MHz, fSAMPLE = 65 MSPS SNR/SFDR (dBFS/dBc) 20 10206-015 10 0 –90 Data Sheet AD9257 450,000 1.0 0.936 LSB RMS 0.8 400,000 0.6 0.4 DNL (LSB) 300,000 250,000 200,000 150,000 0.2 0 –0.2 2.0 1.2 0.8 0.4 0 –0.4 –0.8 –1.2 –1.6 16500 10206-018 15000 13500 12000 10500 9000 7500 6000 4500 3000 1500 –2.0 0 INL (LSB) Figure 19. INL, fIN = 9.7 MHz, fSAMPLE = 65 MSPS Rev. A | Page 13 of 40 16500 10206-019 15000 13500 12000 10500 OUTPUT CODE Figure 20. DNL, fIN = 9.7 MHz, fSAMPLE = 65 MSPS 1.6 OUTPUT CODE 9000 10206-017 OUTPUT CODE Figure 18. Input-Referred Noise Histogram, fSAMPLE = 65 MSPS 7500 –1.0 6000 0 4500 –0.8 3000 50,000 0 –0.6 1500 –0.4 100,000 N – 10 N–9 N–8 N–7 N–6 N–5 N–4 N–3 N–2 N–1 N N+1 N+2 N+3 N+4 N+5 N+6 N+7 N+8 N+9 N + 10 NUMBER OF HITS 350,000 AD9257 Data Sheet AD9257-40 0 0 40MSPS 9.7MHz AT –1dBFS SNR = 74.8dB (75.8dBFS) SFDR = 96.9dBc –30 AMPLITUDE (dBFS) –45 –60 –75 –90 –60 –75 –90 –105 –105 –120 –120 2 4 10 8 6 12 14 16 18 FREQUENCY (MHz) –135 10206-020 –135 4 2 8 6 10 12 14 16 18 FREQUENCY (MHz) Figure 21. Single-Tone 16k FFT with fIN = 9.7 MHz, fSAMPLE = 40 MSPS Figure 24. Single-Tone 16k FFT with fIN = 19.7 MHz, fSAMPLE = 40 MSPS, CLK Divider = 8 0 0 40MSPS 30.5MHz AT –1dBFS SNR = 74.6dB (75.6dBFS) SFDR = 98.8dBc –15 –30 –45 –60 –75 –90 –45 –60 –75 –90 –105 –105 –120 –120 2 4 6 8 10 12 14 16 18 FREQUENCY (MHz) –135 10206-021 –135 40MSPS 69.5MHz AT –1dBFS SNR = 73.7dB (74.7dBFS) SFDR = 87.9dBc –15 AMPLITUDE (dBFS) –30 AMPLITUDE (dBFS) –45 2 4 6 8 10 12 14 16 10206-024 AMPLITUDE (dBFS) –30 40MSPS 19.7MHz AT –1dBFS SNR = 74.9dB (75.9dBFS) SFDR = 94.6dBc –15 10206-023 –15 18 FREQUENCY (MHz) Figure 22. Single-Tone 16k FFT with fIN = 30.5 MHz, fSAMPLE = 40 MSPS, CLK Divider = 8 Figure 25. Single-Tone 16k FFT with fIN = 69.5 MHz, fSAMPLE = 40 MSPS, CLK Divider = 8 0 0 –15 –20 SFDR (dBc) SFDR/IMD3 (dBc/dBFS) AMPLITUDE (dBFS) –30 –45 –60 –75 –90 –105 F2 – F1 2F2 – F1 + 2F1 + F2 2F2 + F1 2F1 – F2 –40 IMD3 (dBc) –60 –80 SFDR (dBFS) F1 + F2 –100 –120 4 6 8 10 12 14 16 18 FREQUENCY (MHz) 10206-022 2 –120 –90 –78 –66 –54 –42 –30 –18 –6 INPUT AMPLITUDE (dBFS) Figure 26. Two-Tone SFDR/IMD3 vs. Input Amplitude (AIN) with fIN1 = 30 MHz and fIN2 = 32 MHz, fSAMPLE = 40 MSPS Figure 23. Two-Tone 16k FFT with fIN1 = 8 MHz and fIN2 = 10 MHz, fSAMPLE = 40 MSPS Rev. A | Page 14 of 40 10206-025 IMD3 (dBFS) –135 Data Sheet AD9257 110 120 SFDR (dBc) 100 SFDRFS 90 SNR/SFDR (dBFS/dBc) SNR/SFDR (dBFS/dBc) 100 SNRFS 80 60 SFDR 40 SNR 80 SNR (dBFS) 70 60 50 40 30 20 20 –70 –60 –40 –50 –30 –20 –10 0 INPUT AMPLITUDE (dBFS) 0 10206-026 –80 0 20 40 60 80 100 120 140 160 180 200 INPUT FREQUENCY (MHz) Figure 27. SNR/SFDR vs. Analog Input Level, fIN = 9.7 MHz, fSAMPLE = 40 MSPS 10206-029 10 0 –90 Figure 30. SNR/SFDR vs. fIN, fSAMPLE = 40 MSPS 105 105 100 100 95 95 SNR/SFDR (dBFS/dBc) 90 85 80 SFDR 90 85 80 SNRFS SNRFS 75 75 30 25 40 35 SAMPLE FREQUENCY (MSPS) 70 20 10206-027 70 20 25 30 35 40 SAMPLE FREQUENCY (MSPS) 10206-030 SNR/SFDR (dBFS/dBc) SFDR Figure 31. SNR/SFDR vs. Encode, fIN = 30.5 MHz, CLK Divider = 4 Figure 28. SNR/SFDR vs. Encode, fIN = 19.7 MHz, CLK Divider = 4 500,000 105 0.91 LSB RMS SFDR (dBc) 450,000 100 NUMBER OF HITS SNR/SFDR (dBFS/dBc) 400,000 95 90 85 350,000 300,000 250,000 200,000 150,000 80 SNR (dBFS) 100,000 75 35 60 85 0 OUTPUT CODE Figure 29. SNR/SFDR vs. Temperature, fIN = 9.7 MHz, fSAMPLE = 40 MSPS Rev. A | Page 15 of 40 Figure 32. Input-Referred Noise Histogram, fSAMPLE = 40 MSPS 10206-031 10 TEMPERATURE (°C) N – 10 N–9 N–8 N–7 N–6 N–5 N–4 N–3 N–2 N–1 N N+1 N+2 N+3 N+4 N+5 N+6 N+7 N+8 N+9 N + 10 –15 10206-028 50,000 70 –40 Data Sheet 1.0 1.6 0.8 1.2 0.6 0.8 0.4 0.4 0.2 0 Figure 34. DNL, fIN = 9.7 MHz, fSAMPLE = 40 MSPS Rev. A | Page 16 of 40 16500 10206-033 OUTPUT CODE Figure 33. INL, fIN = 9.7 MHz, fSAMPLE = 40 MSPS 15000 13500 12000 10500 9000 7500 6000 0 16500 10206-032 OUTPUT CODE 15000 13500 12000 10500 –1.0 9000 –2.0 7500 –0.8 6000 –1.6 4500 –0.6 3000 –0.4 –1.2 1500 –0.8 4500 –0.2 3000 0 –0.4 1500 DNL (LSB) 2.0 0 INL (LSB) AD9257 Data Sheet AD9257 EQUIVALENT CIRCUITS AVDD AVDD 350Ω SCLK/DTP, SYNC, AND PDWN 30kΩ 10206-034 10206-038 VIN± x Figure 35. Equivalent Analog Input Circuit Figure 39. Equivalent SCLK/DTP, SYNC, and PDWN Input Circuit AVDD 10Ω CLK+ AVDD 15kΩ 0.9V AVDD 375Ω RBIAS AND VCM 15kΩ 10206-035 10206-039 10Ω CLK– Figure 40. Equivalent RBIAS, VCM Circuit Figure 36. Equivalent Clock Input Circuit AVDD AVDD 30kΩ 400Ω 31kΩ 350Ω 10206-040 CSB 10206-036 SDIO/DFS Figure 41. Equivalent CSB Input Circuit Figure 37. Equivalent SDIO/DFS Input Circuit DRVDD AVDD V V D– x D+ x V V 375Ω VREF 10206-037 DRGND 10206-041 7.5kΩ Figure 42. Equivalent VREF Circuit Figure 38. Equivalent Digital Output Circuit Rev. A | Page 17 of 40 AD9257 Data Sheet THEORY OF OPERATION The AD9257 is a multistage, pipelined ADC. Each stage provides sufficient overlap to correct for flash errors in the preceding stage. The quantized outputs from each stage are combined into a final 14-bit result in the digital correction logic. The serializer transmits this converted data in a 14-bit output. The pipelined architecture permits the first stage to operate with a new input sample while the remaining stages operate with preceding samples. Sampling occurs on the rising edge of the clock. Each stage of the pipeline, excluding the last, consists of a low resolution flash ADC connected to a switched-capacitor DAC and an interstage residue amplifier (for example, a multiplying digital-to-analog converter (MDAC)). The residue amplifier magnifies the difference between the reconstructed DAC output and the flash input for the next stage in the pipeline. One bit of redundancy is used in each stage to facilitate digital correction of flash errors. The last stage simply consists of a flash ADC. The output staging block aligns the data, corrects errors, and passes the data to the output buffers. The data is then serialized and aligned to the frame and data clocks. ANALOG INPUT CONSIDERATIONS The analog input to the AD9257 is a differential switchedcapacitor circuit designed for processing differential input signals. This circuit can support a wide common-mode range while maintaining excellent performance. By using an input common-mode voltage of midsupply, users can minimize signal-dependent errors and achieve optimum performance. the output stage of the driving source. In addition, low Q inductors or ferrite beads can be placed on each leg of the input to reduce high differential capacitance at the analog inputs and, therefore, achieve the maximum bandwidth of the ADC. Such use of low Q inductors or ferrite beads is required when driving the converter front end at high IF frequencies. Either a differential capacitor or two single-ended capacitors can be placed on the inputs to provide a matching passive network. This ultimately creates a low-pass filter at the input to limit unwanted broadband noise. See the AN-742 Application Note, the AN-827 Application Note, and the Analog Dialogue article “Transformer-Coupled Front-End for Wideband A/D Converters” (Volume 39, April 2005) for more information. In general, the precise values depend on the application. Input Common Mode The analog inputs of the AD9257 are not internally dc-biased. Therefore, in ac-coupled applications, the user must provide this bias externally. Setting the device so that VCM = AVDD/2 is recommended for optimum performance, but the device can function over a wider range with reasonable performance, as shown in Figure 44. An on-board, common-mode voltage reference is included in the design and is available from the VCM pin. The VCM pin must be decoupled to ground by a 0.1 µF capacitor, as described in the Applications Information section. Maximum SNR performance is achieved by setting the ADC to the largest span in a differential configuration. In the case of the AD9257, the largest input span available is 2 V p-p. 100 SFDR H 90 CPAR 80 SNR/SFDR (dBFS/dBc) H CSAMPLE S S S S CSAMPLE VIN– x H H 70 60 50 40 10206-042 CPAR SNRFS 30 Figure 43. Switched-Capacitor Input Circuit The clock signal alternately switches the input circuit between sample mode and hold mode (see Figure 43). When the input circuit is switched to sample mode, the signal source must be capable of charging the sample capacitors and settling within one-half of a clock cycle. A small resistor in series with each input can help reduce the peak transient current injected from Rev. A | Page 18 of 40 20 0.5 0.7 0.9 1.1 VCM (V) Figure 44. SNR/SFDR vs. Common-Mode Voltage, fIN = 9.7 MHz, fSAMPLE = 65 MSPS 1.3 10206-043 VIN+ x Data Sheet AD9257 Differential Input Configurations Internal Reference Connection There are several ways to drive the AD9257 either actively or passively. However, optimum performance is achieved by driving the analog input differentially. Using a differential double balun configuration to drive the AD9257 provides excellent performance and a flexible interface to the ADC (see Figure 46) for baseband applications. A comparator within the AD9257 detects the potential at the SENSE pin and configures the reference into two possible modes, which are summarized in Table 9. If SENSE is grounded, the reference amplifier switch is connected to the internal resistor divider (see Figure 45), setting VREF to 1.0 V. Table 9. Reference Configuration Summary For applications where SNR is a key parameter, differential transformer coupling is the recommended input configuration (see Figure 47), because the noise performance of most amplifiers is not adequate to achieve the true performance of the AD9257. Selected Mode Fixed Internal Reference Fixed External Reference Regardless of the configuration, the value of the shunt capacitor, C, is dependent on the input frequency and may need to be reduced or removed. SENSE Voltage (V) AGND to 0.2 Resulting VREF (V) 1.0 internal AVDD 1.0 applied to external VREF pin It is not recommended to drive the AD9257 input single-ended. Resulting Differential Span (V p-p) 2.0 2.0 VIN+ x VOLTAGE REFERENCE VIN– x A stable and accurate 1.0 V voltage reference is built into the AD9257. VREF can be configured using either the internal 1.0 V reference or an externally applied 1.0 V reference voltage. The various reference modes are summarized in the sections that follow. The VREF pin should be externally decoupled to ground with a low ESR, 1.0 μF capacitor in parallel with a low ESR, 0.1 μF ceramic capacitor. ADC CORE VREF 1.0µF 0.1µF SELECT LOGIC SENSE ADC Figure 45. Internal Reference Configuration 0.1µF 0.1µF R C 33Ω 33Ω 2V p-p *C1 VIN+ x ADC 5pF C 33Ω 0.1µF R VCM VIN– x ET1-1-I3 33Ω C *C1 200Ω 0.1µF C 0.1µF *C1 IS OPTIONAL Figure 46. Differential Double Balun Input Configuration for Baseband Applications ADT1-1WT 1:1 Z RATIO R *C1 VIN+ x 33Ω 49.9Ω C ADC 5pF R 33Ω VIN– x VCM *C1 200Ω 0.1µF 0.1μF *C1 IS OPTIONAL Figure 47. Differential Transformer-Coupled Configuration for Baseband Applications Rev. A | Page 19 of 40 10206-046 2V p-p 10206-045 R 10206-044 0.5V AD9257 Data Sheet If the internal reference of the AD9257 is used to drive multiple converters to improve gain matching, the loading of the reference by the other converters must be considered. Figure 48 shows how the internal reference voltage is affected by loading. 0 –0.5 INTERNAL VREF = 1V VREF ERROR (%) The AD9257 has a very flexible clock input structure. The clock input can be a CMOS, LVDS, LVPECL, or sine wave signal. Regardless of the type of signal being used, clock source jitter is of the utmost concern, as described in the Jitter Considerations section. –2.0 –2.5 –3.0 –3.5 –4.0 –5.0 0 0.5 1.0 1.5 2.0 2.5 3.0 LOAD CURRENT (mA) 10206-047 –4.5 Figure 48. VREF Error vs. Load Current External Reference Operation The use of an external reference may be necessary to enhance the gain accuracy of the ADC or improve thermal drift characteristics. Figure 49 shows the typical drift characteristics of the internal reference in 1.0 V mode. Figure 50 and Figure 51 show two preferred methods for clocking the AD9257 (at clock rates of up to 520 MHz prior to the internal CLK divider). A low jitter clock source is converted from a single-ended signal to a differential signal using either an RF transformer or an RF balun. The RF balun configuration is recommended for clock frequencies between 65 MHz and 520 MHz, and the RF transformer is recommended for clock frequencies from 10 MHz to 200 MHz. The back-to-back Schottky diodes across the transformer/balun secondary winding limit clock excursions into the AD9257 to approximately 0.8 V p-p differential. This limit helps prevent the large voltage swings of the clock from feeding through to other portions of the AD9257 while preserving the fast rise and fall times of the signal that are critical to a low jitter performance. However, the diode capacitance comes into play at frequencies above 500 MHz. Care must be taken in choosing the appropriate signal limiting diode. 4 2 VREF ERROR (mV) For optimum performance, clock the AD9257 sample clock inputs, CLK+ and CLK−, with a differential signal. The signal is typically ac-coupled into the CLK+ and CLK− pins via a transformer or capacitors. These pins are biased internally (see Figure 36) and require no external bias. Clock Input Options –1.0 –1.5 CLOCK INPUT CONSIDERATIONS 0 –2 Mini-Circuits® ADT1-1WT, 1:1 Z –4 0.1µF CLOCK INPUT –6 XFMR 0.1µF CLK+ 100Ω 50Ω ADC 0.1µF CLK– 35 TEMPERATURE (°C) 60 85 SCHOTTKY DIODES: HSMS2822 0.1µF 10206-049 10 Figure 50. Transformer-Coupled Differential Clock (Up to 200 MHz) Figure 49. Typical VREF Drift When the SENSE pin is tied to AVDD, the internal reference is disabled, allowing the use of an external reference. An internal reference buffer loads the external reference with an equivalent 7.5 kΩ load (see Figure 42). The internal buffer generates the positive and negative full-scale references for the ADC core. Therefore, the external reference must be limited to a maximum of 1.0 V. It is not recommended to leave the SENSE pin floating. 0.1µF CLOCK INPUT 0.1µF CLK+ 50Ω ADC 0.1µF 0.1µF CLK– SCHOTTKY DIODES: HSMS2822 Figure 51. Balun-Coupled Differential Clock (65 MHz to 520 MHz) Rev. A | Page 20 of 40 10206-050 –15 10206-048 –8 –40 Data Sheet AD9257 This synchronization feature allows multiple parts to have their clock dividers aligned to guarantee simultaneous input sampling. If a low jitter clock source is not available, another option is to ac couple a differential PECL signal to the sample clock input pins, as shown in Figure 52. The AD9510/AD9511/AD9512/ AD9513/AD9514/AD9515/AD9516/AD9517 clock drivers offer excellent jitter performance. Clock Duty Cycle Typical high speed ADCs use both clock edges to generate a variety of internal timing signals and, as a result, may be sensitive to clock duty cycle. Commonly, a ±5% tolerance is required on the clock duty cycle to maintain dynamic performance characteristics. A third option is to ac couple a differential LVDS signal to the sample clock input pins, as shown in Figure 53. The AD9510/ AD9511/AD9512/AD9513/AD9514/AD9515/AD9516/AD9517 clock drivers offer excellent jitter performance. The AD9257 contains a duty cycle stabilizer (DCS) that retimes the nonsampling (falling) edge, providing an internal clock signal with a nominal 50% duty cycle. This allows the user to provide a wide range of clock input duty cycles without affecting the performance of the AD9257. Noise and distortion performance are nearly flat for a wide range of duty cycles with the DCS on. In some applications, it may be acceptable to drive the sample clock inputs with a single-ended 1.8 V CMOS signal. In such applications, drive the CLK+ pin directly from a CMOS gate, and bypass the CLK− pin to ground with a 0.1 μF capacitor (see Figure 54). Jitter in the rising edge of the input is still of concern and is not easily reduced by the internal stabilization circuit. The duty cycle control loop does not function for clock rates less than 20 MHz, nominally. The loop has a time constant associated with it that must be considered in applications in which the clock rate can change dynamically. A wait time of 1.5 µs to 5 µs is required after a dynamic clock frequency increase or decrease before the DCS loop is relocked to the input signal. Input Clock Divider The AD9257 contains an input clock divider with the ability to divide the input clock by integer values between 1 and 8. The AD9257 clock divider can be synchronized using the external SYNC input. Bit 0 and Bit 1 of Register 0x109 allow the clock divider to be resynchronized on every SYNC signal or only on the first SYNC signal after the register is written. A valid SYNC causes the clock divider to reset to its initial state. 0.1µF 0.1µF CLOCK INPUT CLK+ AD951x PECL DRIVER 0.1µF 100Ω ADC 0.1µF CLK– 50kΩ 240Ω 50kΩ 10206-051 CLOCK INPUT 240Ω Figure 52. Differential PECL Sample Clock (Up to 520 MHz) 0.1µF 0.1µF CLOCK INPUT CLK+ 0.1µF 100Ω ADC 0.1µF CLK– 50kΩ 10206-052 CLOCK INPUT AD951x LVDS DRIVER 50kΩ Figure 53. Differential LVDS Sample Clock (Up to 520 MHz) VCC 0.1µF 50Ω1 1kΩ AD951x CMOS DRIVER OPTIONAL 0.1µF 100Ω 1kΩ CLK+ ADC CLK– 0.1µF 150Ω RESISTOR IS OPTIONAL. Figure 54. Single-Ended 1.8 V CMOS Input Clock (Up to 200 MHz) Rev. A | Page 21 of 40 10206-053 CLOCK INPUT AD9257 Data Sheet Jitter Considerations POWER DISSIPATION AND POWER-DOWN MODE High speed, high resolution ADCs are sensitive to the quality of the clock input. The degradation in SNR at a given input frequency (fA) due only to aperture jitter (tJ) can be calculated by As shown in Figure 56, the power dissipated by the AD9257 is proportional to its sample rate. The digital power dissipation does not vary significantly because it is determined primarily by the DRVDD supply and bias current of the LVDS output drivers. 400 The clock input should be treated as an analog signal in cases where aperture jitter may affect the dynamic range of the AD9257. Power supplies for clock drivers should be separated from the ADC output driver supplies to avoid modulating the clock signal with digital noise. Low jitter, crystal-controlled oscillators make the best clock sources. If the clock is generated from another type of source (by gating, dividing, or other methods), it should be retimed by the original clock at the last step. Refer to the AN-501 Application Note and the AN-756 Application Note for more in-depth information about jitter performance as it relates to ADCs. 130 RMS CLOCK JITTER REQUIREMENT 90 14 BITS 80 12 BITS 70 10 BITS 60 8 BITS 50 40 0.125ps 0.25ps 0.5ps 1.0ps 2.0ps 30 1 10 100 ANALOG INPUT FREQUENCY (MHz) Figure 55. Ideal SNR vs. Input Frequency and Jitter 1000 10206-054 SNR (dB) 110 16 BITS 65MSPS 300 50MSPS 250 40MSPS 200 20MSPS 150 10 20 30 40 50 60 SAMPLE RATE (MSPS) Figure 56. Analog Core Power vs. fSAMPLE for fIN = 9.7 MHz The AD9257 is placed in power-down mode either by the SPI port or by asserting the PDWN pin high. In this state, the ADC typically dissipates 1 mW. During power-down, the output drivers are placed in a high impedance state. Asserting the PDWN pin low returns the AD9257 to its normal operating mode. Note that PDWN is referenced to the digital output driver supply (DRVDD) and should not exceed that supply voltage. 120 100 350 10206-055 In this equation, the rms aperture jitter represents the root mean square of all jitter sources, including the clock input, analog input signal, and ADC aperture jitter specifications. IF undersampling applications are particularly sensitive to jitter (see Figure 55). ANALOG CORE POWER (mW) 1 SNR Degradation = 20 log10 2π × f × t J A Low power dissipation in power-down mode is achieved by shutting down the reference, reference buffer, biasing networks, and clock. Internal capacitors are discharged when entering powerdown mode and then must be recharged when returning to normal operation. As a result, wake-up time is related to the time spent in power-down mode, and shorter power-down cycles result in proportionally shorter wake-up times. When using the SPI port interface, the user can place the ADC in power-down mode or standby mode. Standby mode allows the user to keep the internal reference circuitry powered when faster wake-up times are required. See the Memory Map section for more details on using these features. Rev. A | Page 22 of 40 Data Sheet AD9257 DIGITAL OUTPUTS AND TIMING The AD9257 LVDS outputs facilitate interfacing with LVDS receivers in custom ASICs and FPGAs for superior switching performance in noisy environments. Single point-to-point net topologies are recommended with a 100 Ω termination resistor placed as close to the receiver as possible. If there is no far-end receiver termination or there is poor differential trace routing, timing errors may result. To avoid such timing errors, it is recommended that the trace length be less than 24 inches and the differential output traces be close together and at equal lengths. An example of the FCO and data stream with proper trace length and position is shown in Figure 57. An example of LVDS output timing in reduced range mode is shown in Figure 58. FCO 500mV/DIV DCO 500mV/DIV DATA 500mV/DIV 5ns/DIV Figure 57. LVDS Output Timing Example in ANSI-644 Mode (Default) FCO 500mV/DIV DCO 500mV/DIV DATA 500mV/DIV 5ns/DIV 10206-057 When operating in reduced range mode, the output current is reduced to 2 mA. This results in a 200 mV swing (or 400 mV p-p differential) across a 100 Ω termination at the receiver. 10206-056 The AD9257 differential outputs conform to the ANSI-644 LVDS standard on default power-up. This can be changed to a low power, reduced signal option (similar to the IEEE 1596.3 standard) via the SPI. The LVDS driver current is derived on chip and sets the output current at each output equal to a nominal 3.5 mA. A 100 Ω differential termination resistor placed at the LVDS receiver inputs results in a nominal 350 mV swing (or 700 mV p-p differential) at the receiver. Figure 58. LVDS Output Timing Example in Reduced Range Mode Rev. A | Page 23 of 40 AD9257 Data Sheet Figure 59 shows an example of the LVDS output using the ANSI-644 standard (default) data eye and a time interval error (TIE) jitter histogram with trace lengths of less than 24 inches on standard FR-4 material. to drive longer trace lengths, which can be achieved by programming Register 0x15. Even though this option produces sharper rise and fall times on the data edges and is less prone to bit errors, it also increases the power dissipation of the DRVDD supply. 400 EYE: ALL BITS 300 ULS: 7000:400354 EYE: ALL BITS ULS: 7000/18200 EYE DIAGRAM VOLTAGE (mV) EYE DIAGRAM VOLTAGE (mV) 300 200 100 0 –100 –200 200 100 0 –100 –200 –300 –300 1.0ns 0.8ns 0.4ns 40ps 0.6ns 0.2ns 20ps 0ns –0.2ns –0.4ns –0.6ns –0.8ns –1.0ns 1.0ns 0.8ns 0.6ns 0.4ns 0.2ns 0ns –0.2ns –0.4ns –0.6ns –0.8ns –1.0ns –400 2.5k 10206-059 80ps 60ps 0ps –20ps 0.5k 0 10206-058 80ps 60ps 40ps 20ps 0ps –20ps 0 –40ps 0.5k 1.0k –40ps 1.0k 1.5k –60ps 1.5k 2.0k –80ps TIE JITTER HISTOGRAM (Hits) 2.0k –60ps TIE JITTER HISTOGRAM (Hits) 2.5k Figure 59. Data Eye for LVDS Outputs in ANSI-644 Mode with Trace Lengths Less Than 24 Inches on Standard FR-4, External 100 Ω Far Termination Only Figure 60. Data Eye for LVDS Outputs in ANSI-644 Mode with Trace Lengths Greater Than 24 Inches on Standard FR-4, External 100 Ω Far Termination Only Figure 60 shows an example of trace lengths exceeding 24 inches on standard FR-4 material. Note that the TIE jitter histogram reflects the decrease of the data eye opening as the edge deviates from the ideal position. The default format of the output data is twos complement. Table 10 shows an example of the output coding format. To change the output data format to offset binary, see the Memory Map section. It is the responsibility of the user to determine if the waveforms meet the timing budget of the design when the trace lengths exceed 24 inches. Additional SPI options allow the user to further increase the internal termination (increasing the current) of all eight outputs Data from each ADC is serialized and provided on a separate channel in DDR mode. The data rate for each serial stream is equal to 14 bits times the sample clock rate, with a maximum of 910 Mbps (14 bits × 65 MSPS) = 910 Mbps. The lowest typical conversion rate is 10 MSPS. See the Memory Map section for details on enabling this feature. Table 10. Digital Output Coding Input (V) VIN+ − VIN− VIN+ − VIN− VIN+ − VIN− VIN+ − VIN− VIN+ − VIN− Condition (V) < −VREF − 0.5 LSB = −VREF =0 = +VREF − 1.0 LSB > +VREF − 0.5 LSB Offset Binary Output Mode 00 0000 0000 0000 00 0000 0000 0000 10 0000 0000 0000 11 1111 1111 1111 11 1111 1111 1111 Rev. A | Page 24 of 40 Twos Complement Mode 10 0000 0000 0000 10 0000 0000 0000 00 0000 0000 0000 01 1111 1111 1111 01 1111 1111 1111 Data Sheet AD9257 Two output clocks are provided to assist in capturing data from the AD9257. The DCO is used to clock the output data and is equal to 7× the sample clock (CLK) rate for the default mode of operation. Data is clocked out of the AD9257 and must be captured on the rising and falling edges of the DCO that supports double data rate (DDR) capturing. The FCO is used to signal the start of a new output byte and is equal to the sample clock rate (see the Timing Diagrams section). When the SPI is used, the DCO phase can be adjusted in 60° increments relative to the data edge. This enables the user to refine system timing margins if required. The default DCO+ and DCO− timing, as shown in Figure 2, is 180° relative to the output data edge. A 12-bit serial stream can also be initiated from the SPI. This allows the user to implement and test compatibility to lower resolution systems. When changing the resolution to a 12-bit serial stream, the data stream is shortened. See Figure 3 for the 12-bit example. In default mode, as shown in Figure 2, the MSB is first in the data output serial stream. This can be inverted so that the LSB is first in the data output serial stream by using the SPI. There are 12 digital output test pattern options available that can be initiated through the SPI. This is a useful feature when validating receiver capture and timing (see Table 11 for the output bit sequencing options that are available). Some test patterns have two serial sequential words and can be alternated in various ways, depending on the test pattern chosen. Note that some patterns do not adhere to the data format select option. In addition, custom user-defined test patterns can be assigned in Register 0x19, Register 0x1A, Register 0x1B, and Register 0x1C. Table 11. Flexible Output Test Modes Digital Output Word 2 N/A N/A N/A Yes Offset binary code shown N/A Yes Offset binary code shown 0101 0101 0101 (12-bit) 01 0101 0101 0101 (14-bit) N/A No PN sequence long 1 Digital Output Word 1 N/A 1000 0000 0000 (12-bit) 10 0000 0000 0000 (14-bit) 1111 1111 1111 (12-bit) 11 1111 1111 1111 (14-bit) 0000 0000 0000 (12-bit) 00 0000 0000 0000 (14-bit) 1010 1010 1010 (12-bit) 10 1010 1010 1010 (14-bit) N/A Subjec t to Data Format Select N/A Yes Yes 0110 PN sequence short1 N/A N/A Yes 0111 0000 0000 0000 (12-bit) 00 0000 0000 0000 (14-bit) Register 0x1B to Register 0x1C N/A No No 1010 1× sync N/A No 1011 One bit high N/A No 1100 Mixed frequency 1111 1111 1111 (12-bit) 11 1111 1111 1111 (14-bit) Register 0x19 to Register 0x1A 1010 1010 1010 (12-bit) 10 1010 1010 1010 (14-bit) 0000 0011 1111 (12-bit) 00 0000 0111 1111 (14-bit) 1000 0000 0000 (12-bit) 10 0000 0000 0000 (14-bit) 1010 0011 0011 (12-bit) 10 1000 0110 0111 (14-bit) No 1000 1001 One-/zero-word toggle User input 1-/0-bit toggle N/A No Output Test Mode Bit Sequence 0000 0001 Pattern Name Off (default) Midscale short 0010 +Full-scale short 0011 −Full-scale short 0100 Checkerboard 0101 1 Notes Offset binary code shown PN23 ITU 0.150 X23 + X18 + 1 PN9 ITU O.150 X9 + X5 + 1 Pattern associated with the external pin All test mode options except PN sequence short and PN sequence long can support 12-bit to 14-bit word lengths to verify data capture to the receiver. Rev. A | Page 25 of 40 AD9257 Data Sheet The PN sequence short pattern produces a pseudorandom bit sequence that repeats itself every 29 − 1 or 511 bits. A description of the PN sequence and how it is generated can be found in Section 5.1 of the ITU-T 0.150 (05/96) standard. The seed value is all 1s (see Table 12 for the initial values). The output is a parallel representation of the serial PN9 sequence in MSB-first format. The first output word is the first 14 bits of the PN9 sequence in MSB aligned form. SCLK/DTP Pin Table 12. PN Sequence alignment adjustments among the FCO, DCO, and output data. This pin has an internal 30 kΩ resistor to GND. It can be left unconnected for normal operation. Sequence PN Sequence Short PN Sequence Long Initial Value 0x1FE0 0x1FFF First Three Output Samples (MSB First) Twos Complement 0x1DF1, 0x3CC8, 0x294E 0x1FE0, 0x2001, 0x1C00 The PN sequence long pattern produces a pseudorandom bit sequence that repeats itself every 223 − 1 or 8,388,607 bits. A description of the PN sequence and how it is generated can be found in Section 5.6 of the ITU-T 0.150 (05/96) standard. The seed value is all 1s (see Table 12 for the initial values) and the AD9257 inverts the bit stream with relation to the ITU standard. The output is a parallel representation of the serial PN23 sequence in MSB-first format. The first output word is the first 14 bits of the PN23 sequence in MSB aligned format. Consult the Memory Map section for information on how to change these additional digital output timing features through the SPI. SDIO/DFS Pin For applications that do not require SPI mode operation, the CSB pin is tied to AVDD, and the SDIO/DFS pin controls the output data format select according to Table 13. The SCLK/DTP pin is for use in applications that do not require SPI mode operation. This pin can enable a single digital test pattern if it and the CSB pin are both held high during device power-up. When SCLK/DTP is tied to AVDD, the ADC channel outputs shift out the following pattern: 10 0000 0000 0000. The FCO and DCO function normally while all channels shift out the repeatable test pattern. This pattern allows the user to perform timing Table 14. Digital Test Pattern Pin Settings Selected DTP Normal Operation DTP Resulting D± x Normal operation 10 0000 0000 0000 Additional and custom test patterns can also be observed when commanded from the SPI port. Consult the Memory Map section for information about the options available. CSB Pin The CSB pin should be tied to AVDD for applications that do not require SPI mode operation. Tying CSB high causes all SCLK and SDIO information to be ignored. RBIAS Pin To set the internal core bias current of the ADC, place a 10.0 kΩ, 1% tolerance resistor to ground at the RBIAS pin. Table 13. Output Data Format Select Pin Settings DFS Pin Voltage AVDD GND (Default) DTP Voltage No connect AVDD Output Mode Twos complement Offset binary Rev. A | Page 26 of 40 Data Sheet AD9257 BUILT-IN OUTPUT TEST MODES The AD9257 includes a built-in test feature designed to enable verification of the integrity of each data output channel, as well as to facilitate board level debugging. Various output test options are provided to place predictable values on the outputs of the AD9257. OUTPUT TEST MODES The output test options are described in Table 17 at Address 0x0D. When an output test mode is enabled, the analog section of the ADC is disconnected from the digital back-end blocks and the test pattern is run through the output formatting block. Some of the test patterns are subject to output formatting, and some are not. The PN generators from the PN sequence tests can be reset by setting Bit 4 or Bit 5 of Register 0x0D. These tests can be performed with or without an analog signal (if present, the analog signal is ignored), but they do require an encode clock. For more information, see the AN-877 Application Note, Interfacing to High Speed ADCs via SPI. Rev. A | Page 27 of 40 AD9257 Data Sheet SERIAL PORT INTERFACE (SPI) The AD9257 serial port interface (SPI) allows the user to configure the converter for specific functions or operations through a structured register space provided inside the ADC. The SPI gives the user added flexibility and customization, depending on the application. Addresses are accessed via the serial port and can be written to or read from via the port. Memory is organized into bytes that can be further divided into fields, which are documented in the Memory Map section. For detailed operational information, see the AN-877 Application Note, Interfacing to High Speed ADCs via SPI. The falling edge of the CSB, in conjunction with the rising edge of the SCLK, determines the start of the framing. An example of the serial timing and its definitions can be found in Figure 61 and Table 5. CONFIGURATION USING THE SPI During an instruction phase, a 16-bit instruction is transmitted. Data follows the instruction phase, and its length is determined by the W0 and W1 bits. Other modes involving the CSB are available. The CSB can be held low indefinitely, which permanently enables the device; this is called streaming. The CSB can stall high between bytes to allow for additional external timing. When CSB is tied high, SPI functions are placed in high impedance mode. This mode turns on any SPI pin secondary functions. Three pins define the SPI of this ADC: the SCLK/DTP pin, the SDIO/DFS pin, and the CSB pin (see Table 15). The SCLK (a serial clock) is used to synchronize the read and write data presented from and to the ADC. The SDIO (serial data input/ output) is a dual-purpose pin that allows data to be sent to and read from the internal ADC memory map registers. The CSB (chip select bar) is an active low control that enables or disables the read and write cycles. In addition to word length, the instruction phase determines whether the serial frame is a read or write operation, allowing the serial port to be used both to program the chip and to read the contents of the on-chip memory. The first bit of the first byte in a multibyte serial data transfer frame indicates whether a read command or a write command is issued. If the instruction is a readback operation, performing a readback causes the serial data input/output (SDIO) pin to change direction from an input to an output at the appropriate point in the serial frame. Table 15. Serial Port Interface Pins SDIO CSB Function Serial clock. The serial shift clock input, which is used to synchronize serial interface reads and writes. Serial data input/output. A dual-purpose pin that typically serves as an input or an output, depending on the instruction being sent and the relative position in the timing frame. Chip select bar. An active low control that gates the read and write cycles. tHIGH tDS tS tDH CSB All data is composed of 8-bit words. Data can be sent in MSBfirst mode or in LSB-first mode. MSB first is the default on power-up and can be changed via the SPI port configuration register. For more information about this and other features, see the AN-877 Application Note, Interfacing to High Speed ADCs via SPI. tCLK tH tLOW SCLK DON’T CARE SDIO DON’T CARE DON’T CARE R/W W1 W0 A12 A11 A10 A9 A8 A7 D5 Figure 61. Serial Port Interface Timing Diagram Rev. A | Page 28 of 40 D4 D3 D2 D1 D0 DON’T CARE 10206-060 Pin SCLK Data Sheet AD9257 HARDWARE INTERFACE The pins described in Table 15 comprise the physical interface between the user programming device and the serial port of the AD9257. The SCLK pin and the CSB pin function as inputs when using the SPI interface. The SDIO pin is bidirectional, functioning as an input during write phases and as an output during readback. The SPI interface is flexible enough to be controlled by either FPGAs or microcontrollers. One method for SPI configuration is described in detail in the AN-812 Application Note, Microcontroller-Based Serial Port Interface (SPI) Boot Circuit. The SPI port should not be active during periods when the full dynamic performance of the converter is required. Because the SCLK signal, the CSB signal, and the SDIO signal are typically asynchronous to the ADC clock, noise from these signals can degrade converter performance. If the on-board SPI bus is used for other devices, it may be necessary to provide buffers between this bus and the AD9257 to prevent these signals from transitioning at the converter inputs during critical sampling periods. Some pins serve a dual function when the SPI interface is not being used. When the pins are strapped to DRVDD or ground during device power-on, they are associated with a specific function. Table 13 and Table 14 describe the strappable functions supported on the AD9257. CONFIGURATION WITHOUT THE SPI In applications that do not interface to the SPI control registers, the SDIO/DFS pin, the SCLK/DTP pin, and the PDWN pin serve as standalone CMOS-compatible control pins. When the device is powered up, it is assumed that the user intends to use the pins as static control lines for the output data format, output digital test pattern, and power-down feature control. In this mode, CSB should be connected to AVDD, which disables the serial port interface. When the device is in SPI mode, the PDWN pin (if enabled) remains active. For SPI control of power-down, the PDWN pin should be set to its default state. SPI ACCESSIBLE FEATURES Table 16 provides a brief description of the general features that are accessible via the SPI. These features are described in detail in the AN-877 Application Note, Interfacing to High Speed ADCs via SPI. The AD9257 part-specific features are described in detail in the Memory Map Register Descriptions section following Table 17, the external memory map register table. Table 16. Features Accessible Using the SPI Feature Name Mode Clock Offset Test I/O Output Mode Output Phase ADC Resolution and Speed Grade Rev. A | Page 29 of 40 Description Allows the user to set either power-down mode or standby mode Allows the user to access the DCS, set the clock divider, set the clock divider phase, and enable the sync Allows the user to digitally adjust the converter offset Allows the user to set test modes to have known data on output bits Allows the user to set the output mode Allows the user to set the output clock polarity Scalable power consumption options based on resolution and speed grade selection AD9257 Data Sheet MEMORY MAP READING THE MEMORY MAP REGISTER TABLE Default Values Each row in the memory map register table has eight bit locations. The memory map is roughly divided into three sections: the chip configuration registers (Address 0x00 to Address 0x02); the device index and transfer registers (Address 0x05 and Address 0xFF); and the global ADC functions registers, including setup, control, and test (Address 0x08 to Address 0x109). After the AD9257 is reset, critical registers are loaded with default values. The default values for the registers are given in Table 17, the memory map register table. Logic Levels An explanation of logic level terminology follows: • The memory map register table (see Table 17) lists the default hexadecimal value for each hexadecimal address shown. The column with the heading Bit 7 (MSB) is the start of the default hexadecimal value given. For example, Address 0x05, the device index register, has a hexadecimal default value of 0x3F. This means that in Address 0x05, Bits[7:6] = 0, and the remaining Bits[5:0] = 1. This setting is the default channel index setting. The default value results in both ADC channels receiving the next write command. For more information on this function and others, see the AN-877 Application Note, Interfacing to High Speed ADCs via SPI. This application note details the functions controlled by Register 0x00 to Register 0xFF. The remaining registers are documented in the Memory Map Register Descriptions section. Open Locations All address and bit locations that are not included in Table 17 are not currently supported for this device. Unused bits of a valid address location should be written with 0s. Writing to these locations is required only when part of an address location is open (for example, Address 0x05). If the entire address location is open or not listed in Table 17 (for example, Address 0x13) this address location should not be written. • “Bit is set” is synonymous with “bit is set to Logic 1” or “writing Logic 1 for the bit.” “Clear a bit” is synonymous with “bit is set to Logic 0” or “writing Logic 0 for the bit.” Channel-Specific Registers Some channel setup functions can be programmed differently for each channel. In these cases, channel address locations are internally duplicated for each channel. These registers and bits are designated in Table 17 as local. These local registers and bits can be accessed by setting the appropriate data channel bits (A through H) and the clock channel DCO/FCO bits (Bits[5:4]) in Registers 0x04 and 0x05. If all the bits are set, the subsequent write affects the registers of all channels and the DCO/FCO clock channels. In a read cycle, only one of the channels should be set to read one of the four local registers. If all the bits are set during a SPI read cycle, the part returns the value for Channel A. Registers and bits designated as global in Table 17 affect the entire part or the channel features for which independent settings are not allowed between channels. The settings in Register 0x04 and Register 0x05 do not affect the global registers and bits. Rev. A | Page 30 of 40 Data Sheet AD9257 MEMORY MAP REGISTER TABLE The AD9257 uses a 3-wire interface and 16-bit addressing and, therefore, Bit 0 and Bit 7 in Register 0x00 are set to 0, and Bit 3 and Bit 4 are set to 1. When Register 0x00, Bit 5 is set high, the SPI enters a soft reset, where all of the user registers revert to their default values and Bit 2 is automatically cleared. Table 17. Memory Map Register Table Reg. Addr. (Hex) Register Name Chip Configuration Registers 0x00 SPI port configuration 0x01 Chip ID (global) 0x02 Chip grade (global) Bit 7 (MSB) 0 = SDO active Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (LSB) LSB first Soft reset 1= 16-bit address 1 = 16-bit address Soft reset LSB first 0 = SDO active 8-bit chip ID, Bits[7:0] AD9257 0x92 = octal 14-bit, 40 MSPS/65 MSPS serial LVDS Open Speed grade ID, Bits[6:4] 001 = 40 MSPS 011 = 65 MSPS Default Value (Hex) 0x18 Read only 0x92 Open Open Open Open Read only Comments The nibbles are mirrored so that LSB or MSB first mode registers correctly. The default for the ADCs is 16-bit mode. Unique chip ID that is used to differentiate devices; read only. Unique speed grade ID used to differentiate graded devices. Read only. Device Index and Transfer Registers 0x04 Device Index 2 Open Open Open Open Data Channel H Data Channel G Data Channel F Data Channel E 0xF 0x05 Device Index 1 Open Open Clock Channel DCO Clock Channe l FCO Data Channel D Data Channel C Data Channel B Data Channel A 0x3F 0xFF Transfer Open Open Open Open Open Open Open Initiate override 0x00 Global ADC Functions 0x08 Power modes (global) Open Open Open Open Internal power-down mode 00 = chip run 01 = full power-down 10 = standby 11 = reset 0x00 Determines various generic modes of chip operation. 0x09 Open Open External powerdown pin function 0 = full powerdown 1= standby Open Open Open 0x01 Turns duty cycle stabilizer on or off. Clock (global) Rev. A | Page 31 of 40 Open Open Open Duty cycle stabilize 0 = off 1 = on Bits are set to determine which device on chip receives the next write command. The default is all devices on chip. Bits are set to determine which device on chip receives the next write command. The default is all devices on chip. Set resolution/ sample rate override. AD9257 Reg. Addr. (Hex) 0x0B Register Name Clock divide (global) Data Sheet Bit 7 (MSB) Open Bit 1 Bit 0 (LSB) Clock divide ratio, Bits[2:0] 000 = divide by 1 001 = divide by 2 010 = divide by 3 011 = divide by 4 100 = divide by 5 101 = divide by 6 110 = divide by 7 111 = divide by 8 Open Open Open Open Open Chop Open Open mode 0 = off 1 = on User input test mode Reset PN Reset Output test mode, Bits[3:0] (local) PN long gen 00 = single 0000 = off (default) short 01 = alternate 0001 = midscale short gen 10 = single once 0010 = positive FS 11 = alternate once 0011 = negative FS (affects user input test 0100 = alternating checkerboard mode only, 0101 = PN 23 sequence Bits[3:0] = 1000) 0110 = PN 9 sequence 0111 = one/zero word toggle 1000 = user input 1001 = 1-/0-bit toggle 1010 = 1× sync 1011 = one bit high 1100 = mixed bit frequency 8-bit device offset adjustment, Bits[7:0] (local) Offset adjust in LSBs from +127 to −128 (twos complement format) Open LVDS-ANSI/ Open Open Open Output Open Output LVDS-IEEE format invert option 0 = offset (local) 0 = LVDSbinary ANSI 1 = twos 1 = LVDScomplement IEEE reduced range link (global) (global); (see Table 18) Open Open Output driver Open Open Open Output termination, drive 0 = 1× Bits[1:0] drive 00 = none 1 = 2× 01 = 200 Ω drive 10 = 100 Ω 0x0C Enhancement control 0x0D Test mode (local except for PN sequence resets) 0x10 Offset adjust (local) 0x14 Output mode 0x15 Output adjust 0x16 Output phase Open 0x18 VREF Open Bit 6 Open Bit 5 Open Bit 4 Open Bit 3 Open 11 = 100 Ω Input clock phase adjust, Bits[6:4] (value is number of input clock cycles of phase delay) (see Table 19) Open Open Open Bit 2 Output clock phase adjust, Bits[3:0] (Setting = 0000 through 1011) (see Table 20) Open Rev. A | Page 32 of 40 Internal VREF adjustment digital scheme, Bits[2:0] 000 = 1.0 V p-p 001 = 1.14 V p-p 010 = 1.33 V p-p 011 = 1.6 V p-p 100 = 2.0 V p-p Default Value (Hex) 0x00 Comments The divide ratio is the value plus 1. 0x00 Enables/ disables chop mode. 0x00 When set, the test data is placed on the output pins in place of normal data. 0x00 Device offset trim. Configures the outputs and the format of the data. 0x01 0x00 Determines LVDS or other output properties. 0x03 On devices that use global clock divide, determines which phase of the divider output is used to supply the output clock. Internal latching is unaffected. Selects and/or adjusts the VREF. 0x04 Data Sheet Reg. Addr. (Hex) 0x19 0x1A 0x1B 0x1C 0x21 Register Name USER_PATT1_LSB (global) USER_PATT1_MSB (global) USER_PATT2_LSB (global) USER_PATT2_MSB (global) Serial control (global) AD9257 Bit 7 (MSB) B7 Bit 6 B6 Bit 5 B5 Bit 4 B4 Bit 3 B3 Bit 2 B2 Bit 1 B1 Bit 0 (LSB) B0 Default Value (Hex) 0x00 B15 B14 B13 B12 B11 B10 B9 B8 0x00 B7 B6 B5 B4 B3 B2 B1 B0 0x00 B15 B14 B13 B12 B11 B10 B9 B8 0x00 PLL low encode rate mode Open Open Open LVDS output LSB first Word-wise DDR, 1-lane, Bits[6:4] 100 = DDR 1-lane Open Open Serial output number of bits 01 = 14 bits 10 = 12 bits 0x22 Serial channel status (local) Open Open 0x100 Resolution/ sample rate override Open Resolution/ sample-rate override enable 0x101 User I/O Control 2 Open Open Open Open Open Open Open 0x102 User I/O Control 3 Open Open Open Open Open Open 0x109 Sync Open Open Open Open VCM powerdown Open Open Sync next only Resolution 01 = 14 bits 10 = 12 bits Open Rev. A | Page 33 of 40 Channel output reset Channel powerdown Sample rate 000 = 20 MSPS 001 = 40 MSPS 010 = 50 MSPS 011 = 65 MSPS 0x41 0x00 0x00 SDIO pulldown Open 0x00 Enable sync 0x00 0x00 Comments User Defined Pattern 1 LSB. User Defined Pattern 1 MSB. User Defined Pattern 2 LSB. User Defined Pattern 2 MSB. Serial stream control. Default causes MSB first and the native bit stream. Used to power down individual sections of a converter. Resolution/ sample rate override (requires transfer bit, 0xFF). Disables SDIO pull-down. VCM control. AD9257 Data Sheet MEMORY MAP REGISTER DESCRIPTIONS For additional information about functions controlled in Register 0x00 to Register 0xFF, see the AN-877 Application Note, Interfacing to High Speed ADCs via SPI. Device Index (Register 0x04 and Register 0x05) There are certain features in the map that can be set independently for each channel, whereas other features apply globally to all channels (depending on context), regardless of which are selected. The first four bits in Register 0x04 and Register 0x05 can be used to select which individual data channels are affected. The output clock channels can be selected in Register 0x05, as well. A smaller subset of the independent feature list can be applied to those devices. Transfer (Register 0xFF) All registers except Register 0x100 are updated the moment they are written. Setting Bit 0 of this transfer register high initializes the settings in the ADC sample rate override register (Address 0x100). Power Modes (Register 0x08) Bits[7:6]—Open Output Mode (Register 0x14) Bit 7—Open Bit 6—LVDS-ANSI/LVDS-IEEE Option Setting this bit chooses the LVDS-IEEE (reduced range) option. The default setting is LVDS-ANSI. As described in Table 18, when LVDS-ANSI or LVDS-IEEE reduced range link is selected, the user can select the driver termination. The driver current is automatically selected to give the proper output swing. Table 18. LVDS-ANSI/LVDS-IEEE Options Output Mode, Bit[6] 0 1 Output Mode LVDS-ANSI LVDS-IEEE reduced range link Output Driver Termination User selectable User selectable Output Driver Current Automatically selected to give proper swing Automatically selected to give proper swing Bits[5:3]—Open Bit 2—Output Invert Setting this bit inverts the output bit stream. Bit 5—External Power-Down Pin Function If set, the external PDWN pin initiates standby mode. If cleared, the external PDWN pin initiates power-down mode. Bits[4:2]—Open Bits[1:0]—Internal Power-Down Mode In normal operation (Bits[1:0] = 00), all ADC channels are active. In power-down mode (Bits[1:0] = 01), the digital data path clocks are disabled while the digital data path is reset. Outputs are disabled. In standby mode (Bits[1:0] = 10), the digital data path clocks and the outputs are disabled. During a digital reset (Bits[1:0] = 11), all the digital data path clocks and the outputs (where applicable) on the chip are reset, except the SPI port. Note that the SPI is always left under control of the user, that is, it is never automatically disabled or in reset (except by power-on reset). Enhancement Control (Register 0x0C) Bits[7:3]—Open Bit 2—Chop Mode Bit 1—Open Bit 0—Output Format By default, this bit is set to send the data output in twos complement format. Resetting this bit changes the output mode to offset binary. Output Adjust (Register 0x15) Bits[7:6]—Open Bits[5:4]—Output Termination These bits allow the user to select the internal termination resistor. Bits[3:1]—Open Bit 0—Output Drive Bit 0 of the output adjust register controls the drive strength on the LVDS driver of the FCO and DCO outputs only. The default values set the drive to 1×. The drive can be increased to 2× by setting the appropriate channel bit in Register 0x05 and then setting Bit 0. These features cannot be used with the output driver termination select. The termination selection takes precedence over the 2× driver strength on FCO and DCO when both the output driver termination and output drive are selected. For applications that are sensitive to offset voltages and other low frequency noise, such as homodyne or direct conversion receivers, chopping in the first stage of the AD9257 is a feature that can be enabled by setting Bit 2. In the frequency domain, chopping translates offsets and other low frequency noise to fCLK/2, where they can be filtered. Bits[1:0]—Open Rev. A | Page 34 of 40 Data Sheet AD9257 Output Phase (Register 0x16) Bit 7—Open Resolution/Sample Rate Override (Register 0x100) Bits[6:4]—Input Clock Phase Adjust When the clock divider (Register 0x0B) is used, the applied clock is at a higher frequency than the internal sampling clock. Bits[6:4] determine at which phase of the external clock sampling occurs. This is only applicable when the clock divider is used. Selecting Bits[6:4] greater than Register 0x0B Bits[2:0] is prohibited. Table 19. Input Clock Phase Adjust Options Input Clock Phase Adjust, Bits[6:4] 000 (Default) 001 010 011 100 101 110 111 Number of Input Clock Cycles of Phase Delay 0 1 2 3 4 5 6 7 This register is designed to allow the user to downgrade the device. Any attempt to upgrade the default speed grade results in a chip power-down. Settings in this register are not initialized until Bit 0 of the transfer register (Register 0xFF) is written high. User I/O Control 2 (Register 0x101) Bits[7:1]—Open Bit 0—SDIO Pull-Down Bit 0 can be set to disable the internal 30 kΩ pull-down on the SDIO pin, which can be used to limit loading when many devices are connected to the SPI bus. User I/O Control 3 (Register 0x102) Bits[7:4]—Open Bit 3—VCM Power-Down Bit 3 can be set high to power down the internal VCM generator. This feature is used when applying an external reference. Bits[2:0]—Open Bits[3:0]—Output Clock Phase Adjust Table 20. Output Clock Phase Adjust Options Output Clock (DCO), Phase Adjust, Bits[3:0] 0000 0001 0010 0011 (Default) 0100 0101 0110 0111 1000 1001 1010 1011 DCO Phase Adjustment (Degrees Relative to D± x Edge) 0 60 120 180 240 300 360 420 480 540 600 660 Rev. A | Page 35 of 40 AD9257 Data Sheet APPLICATIONS INFORMATION DESIGN GUIDELINES Before starting design and layout of the AD9257 as a system, it is recommended that the designer become familiar with these guidelines, which describes the special circuit connections and layout requirements that are needed for certain pins. POWER AND GROUND RECOMMENDATIONS When connecting power to the AD9257, it is recommended that two separate 1.8 V supplies be used. Use one supply for analog (AVDD); use a separate supply for the digital outputs (DRVDD). For both AVDD and DRVDD, several different decoupling capacitors should be used to cover both high and low frequencies. Place these capacitors close to the point of entry at the PCB level and close to the pins of the part, with minimal trace length. EXPOSED PAD THERMAL HEAT SLUG RECOMMENDATIONS It is required that the exposed pad on the underside of the ADC be connected to analog ground (AGND) to achieve the best electrical and thermal performance of the AD9257. An exposed continuous copper plane on the PCB should mate to the AD9257 exposed pad, Pin 0. The copper plane should have several vias to achieve the lowest possible resistive thermal path for heat dissipation to flow through the bottom of the PCB. These vias should be solder-filled or plugged. A single PCB ground plane should be sufficient when using the AD9257. With proper decoupling and smart partitioning of the PCB analog, digital, and clock sections, optimum performance is easily achieved. To maximize the coverage and adhesion between the ADC and PCB, partition the continuous copper plane by overlaying a silkscreen on the PCB into several uniform sections. This provides several tie points between the ADC and PCB during the reflow process, whereas using one continuous plane with no partitions guarantees only one tie point. For detailed information on packaging and the PCB layout of chip scale packages, see the AN-772 Application Note, A Design and Manufacturing Guide for the Lead Frame Chip Scale Package (LFCSP), at www.analog.com. CLOCK STABILITY CONSIDERATIONS VCM When powered on, the AD9257 goes into an initialization phase where an internal state machine sets up the biases and the registers for proper operation. During the initialization process, the AD9257 needs a stable clock. If the ADC clock source is not present or not stable during ADC power-up, it will disrupt the state machine and cause the ADC to start up in an unknown state. To correct this, an initialization sequence needs to be re-invoked after the ADC clock is stable. This is done by issuing a digital reset via Register 0x08. In the default configuration (internal VREF, ac-coupled input) where VREF and VCM are supplied by the ADC itself, a stable clock during power-up is sufficient. In the case where VREF and/or VCM are supplied by an external source, these too should be stable at power up; otherwise, a subsequent digital reset via Register 0x08 will be needed. The pseudo-code sequence for a digital reset is as follows: The VCM pin should be decoupled to ground with a 0.1 μF capacitor. SPI_Write (0x08, 0x03); # Digital Reset REFERENCE DECOUPLING The VREF pin should be externally decoupled to ground with a low ESR, 1.0 μF capacitor in parallel with a low ESR, 0.1 μF ceramic capacitor. SPI PORT The SPI port should not be active during periods when the full dynamic performance of the converter is required. Because the SCLK, CSB, and SDIO signals are typically asynchronous to the ADC clock, noise from these signals can degrade converter performance. If the on-board SPI bus is used for other devices, it may be necessary to provide buffers between this bus and the AD9257 to keep these signals from transitioning at the converter inputs during critical sampling periods. SPI_Write (0x08, 0x00); # Normal Operation Rev. A | Page 36 of 40 Data Sheet AD9257 OUTLINE DIMENSIONS 9.10 9.00 SQ 8.90 0.30 0.25 0.18 0.60 MAX 0.60 MAX 64 1 49 48 PIN 1 INDICATOR PIN 1 INDICATOR 8.85 8.75 SQ 8.65 0.50 BSC 0.50 0.40 0.30 33 32 0.25 MIN 0.20 REF FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. COMPLIANT TO JEDEC STANDARDS MO-220-VMMD-4 06-12-2012-C 0.05 MAX 0.02 NOM SEATING PLANE 16 7.50 REF 0.80 MAX 0.65 TYP 12° MAX 17 BOTTOM VIEW TOP VIEW 1.00 0.85 0.80 6.35 6.20 SQ 6.05 EXPOSED PAD Figure 62. 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 9 mm × 9 mm Body, Very Thin Quad (CP-64-4) Dimensions shown in millimeters ORDERING GUIDE Model1 AD9257BCPZ-40 AD9257BCPZRL7-40 AD9257BCPZ-65 AD9257BCPZRL7-65 AD9257-65EBZ 1 Temperature Range −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C Package Description 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] Evaluation Board Z = RoHS Compliant Part. Rev. A | Page 37 of 40 Package Option CP-64-4 CP-64-4 CP-64-4 CP-64-4 AD9257 Data Sheet NOTES Rev. A | Page 38 of 40 Data Sheet AD9257 NOTES Rev. A | Page 39 of 40 AD9257 Data Sheet NOTES ©2011–2013 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D10206-0-4/13(A) Rev. A | Page 40 of 40