16-Bit, 400 MSPS D/A Converter AD9726 FEATURES FUNCTIONAL BLOCK DIAGRAM CLK+ CLK– CLOCK DISTRIBUTION AND CONTROL CSB SCLK SPI DCLK_OUT– SDO LVDS OUTPUT DRIVER RESET CALIBRATION MEMORY DB[0]+ DB[0]– DCLK_IN+ APPLICATIONS DATA SYNCHRONIZATION DB[15]+ DB[15]– 16-BIT DAC IOUTA IOUTB REFIO INTERNAL REFERENCE DCLK_IN– Instrumentation Test equipment Waveform synthesis Communications systems SDIO FSADJ 04540-001 DCLK_OUT+ LVDS INPUT DATA CAPTURE Dynamic performance SFDR ≥ 78 dBc @ fOUT = 20 MHz IMD ≥ 82 dBc @ fOUT = 70 MHz ACLR ≥ 76 dBc @ fOUT = 70 MHz NSD ≤ –160 dB/Hz @ fOUT = 70 MHz Precision calibrated linearity DNL ≤ ±0.5 LSB @ +25°C INL ≤ ±1.0 LSB @ +25°C THD ≤ –95 dB @ fOUT = 1 MHz LVDS inputs with internal 100 Ω terminations Automatic data/clock timing synchronization Single data rate or double data rate capable Differential current outputs Internal precision reference Operates on 2.5 V and 3.3 V supplies Extended industrial temperature range Thermally enhanced, 80-lead, lead-free TQFP_EP package Figure 1. . GENERAL DESCRIPTION PRODUCT HIGHLIGHTS The AD9726 is a 16-bit digital-to-analog converter (DAC) that offers leading edge performance at conversion rates up to 400 MSPS. The device uses low voltage differential signaling (LVDS) inputs and includes internal 100 Ω terminations. The analog output can be single-ended or differential current. An internal precision reference is included. 1. A unique combination of precision and performance makes the AD9726 equally suited to applications with demanding frequency domain or demanding time domain requirements. 2. Nonvolatile factory calibration assures a highly linear transfer function. Internal logic offers on demand selfcalibration for linearity even at extended operating temperatures. 3. Proprietary architecture minimizes data dependent, discrete mixing spurs and offers enhanced dynamic performance over a wide range of output frequencies. High input data rates create a very high frequency synthesis bandwidth. 4. The fully automatic, transparent synchronizer maintains optimized timing between clock and data in real time and offers programmable control options for added flexibility. 5. Full-scale output current is external resistor programmable. The AD9726 also features synchronization logic to monitor and optimizes the timing between incoming data and the sample clock. This reduces system complexity and simplifies timing requirements. An LVDS clock output is also available to drive an external data pump in either single data rate (SDR) or double data rate (DDR) mode. All device operation is fully programmable using the flexible serial port interface (SPI). The AD9726 is also fully functional in its default state for applications without a controller. Rev. A 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 www.analog.com Fax: 781.461.3113 © 2005 Analog Devices, Inc. All rights reserved. AD9726 TABLE OF CONTENTS Features .............................................................................................. 1 Serial Port Interface........................................................................ 13 Applications....................................................................................... 1 Theory of Operation ...................................................................... 15 Functional Block Diagram .............................................................. 1 DAC Clock and Data Clock Output ........................................ 15 General Description ......................................................................... 1 Data Clock Input ........................................................................ 15 Product Highlights ........................................................................... 1 Data Synchronization Circuitry ............................................... 16 Specifications..................................................................................... 3 Analog Output ............................................................................ 16 DC Specifications ......................................................................... 3 Internal Reference and Full-Scale Output .............................. 16 AC Specifications.......................................................................... 4 Reset ............................................................................................. 17 Digital Signal Specifications........................................................ 5 Serial Port Interface ................................................................... 17 Timing Specifications .................................................................. 5 SPI Pin Description.................................................................... 18 Timing Diagrams.......................................................................... 6 Calibration................................................................................... 18 Absolute Maximum Ratings............................................................ 7 Sync Logic Operation and Programming ............................... 20 Thermal Resistance ...................................................................... 7 Outline Dimensions ....................................................................... 22 ESD Caution.................................................................................. 7 Ordering Guide .......................................................................... 22 Pin Configuration and Function Descriptions............................. 8 Terminology .................................................................................... 10 Typical Performance Characteristics ........................................... 11 REVISION HISTORY 11/05—Rev. 0 to Rev. A Changes to Features.......................................................................... 1 Changes to Table 3 and Table 4....................................................... 5 Changes to the Terminology Section........................................... 10 Changes to the Driving the DAC Clock Inputs Section............ 15 Changes to the Reset and Serial Port Interface Sections ........... 17 Updated Outline Dimensions ....................................................... 22 Changes to the Ordering Guide.................................................... 22 7/05—Revision 0: Initial Version Rev. A | Page 2 of 24 AD9726 SPECIFICATIONS DC SPECIFICATIONS DBVDD = AVDD1 = AVDD2 = 3.3 V, DVDD = CLKVDD = ADVDD = ACVDD = 2.5 V, IOUT-FS = 20 mA, internal reference, TMIN to TMAX, unless otherwise specified. Table 1. Parameter ACCURACY1 DNL INL Offset Error Gain Error ANALOG OUTPUT Full-Scale Current Compliance Voltage Output Impedance INTERNAL REFERENCE Output Voltage Output Current2 EXTERNAL REFERENCE Input Voltage Input Resistance Small Signal Bandwidth TEMPERATURE COEFFICIENTS Gain Drift Offset Drift Reference Drift POWER SUPPLIES3 AVDD1, AVDD2 Voltage Range Supply Current (IAVDD1 + IAVDD2) ADVDD, ACVDD Voltage Range Supply Current (IACVDD + IADVDD) CLKVDD Voltage Range Supply Current (ICLKVDD) DVDD Voltage Range Supply Current (IDVDD) DBVDD Voltage Range Supply Current (IDBVDD) POWER DISSIPATION (PDISS) Sleep Mode Power-Down Mode OPERATING TEMPERATURE RANGE Min Typ Max Unit ±0.5 ±1.0 0.003 0.003 ±1.0 ±2.5 LSB LSB % FS % FS 20 ±1 10 1.18 1.22 1 ±10 ±10 ±30 ppm of FS/ºC ppm of FS/ºC ppm/ºC 52 3.47 60 V mA 16 2.63 18 V mA 45 2.63 50 V mA 80 2.63 90 V mA 3.47 18 V mA mW mW mW °C 2.37 2.37 3.13 16 575 465 ≤10 TAMB = 25°C. Use buffer amplifier to drive external load. 3 Supply currents and power dissipation measured in SDR with fDAC = 400 MHz and fOUT = 1 MHz. 2 Rev. A | Page 3 of 24 V µA V MΩ kHz 2.37 1 1.27 1.2 10 200 3.13 –40 mA V MΩ +85 AD9726 AC SPECIFICATIONS DBVDD = AVDD1 = AVDD2 = 3.3 V, DVDD = CLKVDD = ADVDD = ACVDD = 2.5 V, IOUT-FS = 20 mA, internal reference, TMIN to TMAX, unless otherwise specified. Table 2. Parameter TOTAL HARMONIC DISTORTION (THD) fDAC = 400 MHz, fOUT = 1 MHz, 0 dBFS SPURIOUS-FREE DYNAMIC RANGE (SFDR) fDAC = 400 MHz, 0 dBFS fOUT = 20 MHz fOUT = 70 MHz fOUT = 140 MHz fDAC = 400 MHz, –3 dBFS fOUT = 20 MHz fOUT = 70 MHz fOUT = 140 MHz fDAC = 200 MHz, 0 dBFS fOUT = 20 MHz fOUT = 70 MHz fDAC = 200 MHz, –3 dBFS fOUT = 20 MHz fOUT = 70 MHz TWO-TONE INTERMODULATION DISTORTION (IMD) fDAC = 400 MHz, 0 dBFS fOUT1 = 20 MHz, fOUT2 = 21 MHz fOUT1 = 70 MHz, fOUT2 = 71 MHz fOUT1 = 140 MHz, fOUT2 = 141 MHz ADJACENT CHANNEL LEAKAGE RATIO (ACLR) fDATA = 245.76 MSPS, fCARRIER = 70 MHz, 1-Carrier WCDMA fDATA = 245.76 MSPS, fCARRIER = 70 MHz, 2-Carrier WCDMA fDATA = 245.76 MSPS, fCARRIER1 = 70 MHz, 4-Carrier WCDMA fDATA = 245.76 MSPS, fCARRIER1 = 70 MHz, 8-Carrier WCDMA NOISE SPECTRAL DENSITY (NSD) fDAC = 400 MHz, fOUT = 70 MHz, 0 dBFS fDAC = 400 MHz, fOUT = 70 MHz, –3 dBFS fDAC = 400 MHz, fOUT = 70 MHz, –6 dBFS UPDATE RATE Min Typ Max –95 dB 78 68 62 dBc dBc dBc 80 70 62 dBc dBc dBc 84 62 dBc dBc 82 68 dBc dBc 86 82 74 dBc dBc dBc 76 70 66 62 dBc dBc dBc dBc –160 –163 –165 0 Rev. A | Page 4 of 24 Unit 400 dBm/Hz dBm/Hz dBm/Hz MSPS AD9726 DIGITAL SIGNAL SPECIFICATIONS DBVDD = AVDD1 = AVDD2 = 3.3 V, DVDD = CLKVDD = ADVDD = ACVDD = 2.5 V, IOUT-FS = 20 mA, internal reference, TMIN to TMAX, unless otherwise specified. Table 3. Parameter DAC CLOCK INPUTS (CLK+/–) Differential Voltage Common-Mode Voltage LVDS INPUTS (DB[15:0]+/–, DCLK_IN+/–) Input Voltage Range Differential Threshold Voltage Differential Input Impedance LVDS OUTPUT (DCLK_OUT+/–) Differential Output Voltage1 Offset Voltage Short-Circuit Output Current CMOS INPUTS (CSB, SCLK, SDIO, RESET) Logic 0 Voltage Logic 1 Voltage Input Current CMOS OUTPUTS (SDO, SDIO) Logic 0 Voltage Logic 1 Voltage Short-Circuit Output Current CONTROL INPUTS (SPI_DIS, SDR_EN) Logic 0 Voltage Logic 1 Voltage Input Current 1 Min Typ 0.5 1.0 1.0 1.25 825 250 1.0 Max Unit V V 1575 100 100 mV mV Ω 400 1.2 20 mV V mA 0.5 V V nA 0.5 V V mA 0.5 V V nA 2.5 1 3.0 10 2.0 1 With 100 Ω external load. TIMING SPECIFICATIONS DBVDD = AVDD1 = AVDD2 = 3.3 V, DVDD = CLKVDD = ADVDD = ACVDD = 2.5 V, IOUT-FS = 20 mA, internal reference, TMIN to TMAX, unless otherwise specified. Table 4. Parameter LVDS DATA BUS DDR DCLK_OUT+/– Propagation Delay (tDCPD-DDR) DDR DB[15:0]+/– Set-Up Time (tDSU-DDR) DDR DB[15:0]+/– Hold Time (tDH-DDR) SDR DCLK_OUT+/– Propagation Delay (tDCPD-SDR) SDR DB[15:0]+/– Set-Up Time (tDSU-SDR) SDR DB[15:0]+/– Hold Time (tDH-SDR) SERIAL PORT INTERFACE SCLK Frequency (fSCLK) SCLK Rise/Fall Time SCLK Pulse Width High (tCPWH) SCLK Pulse Width Low (tCPWL) SCLK Set-Up Time (tCSU) SDIO Set-Up Time (tDSU) SDIO Hold Time (tDH) SDIO/SDO Valid Time (tDV) RESET PULSE WIDTH Min Typ Max Unit 2000 ps ps ps ps ps ps –100 500 300 –100 500 15 1 30 30 30 30 0 30 1.5 Rev. A | Page 5 of 24 MHz ms ns ns ns ns ns ns ns AD9726 TIMING DIAGRAMS DAC CLOCK tDCPD-DDR DATACLOCK OUTPUT DATA BUS tDH-DDR 04540-002 tDSU-DDR DATACLOCK INPUT Figure 2. DDR Timing Diagram DAC CLOCK tDCPD-SDR DATACLOCK OUTPUT DATA BUS tDH-SDR 04540-003 tDSU-SDR DATACLOCK INPUT Figure 3. SDR Timing Diagram CSB SCLK SET-UP TIME tCSU SCLK PULSE WIDTH HIGH/LOW TIME tCPWH tCPWL SCLK SDIO SET-UP TIME SDIO HOLD TIME tDH SDIO (SD0) VALID TIME tDV 04540-004 tDSU SDIO (SD0) Figure 4. SPI Timing Diagram Rev. A | Page 6 of 24 AD9726 ABSOLUTE MAXIMUM RATINGS Table 5. Parameter DBVDD, AVDD1, AVDD2 DVDD, CLKVDD, ACVDD, ADVDD DBGND, AGND1, AGND2 DGND, CLKGND, ACGND, ADGND REFIO, FSDAJ With Respect to DBGND, AGND1, AGND2 DGND, CLKGND, ACGND, ADGND DBGND, AGND1, AGND2 DGND, CLKGND, ACGND, ADGND AGND1 IOUTA, IOUTB AGND1 CLK+, CLK– CLKGND DB[15:0]+/–, DCLK_IN+/–, DCLK_OUT+/– CSB, SCLK, SDIO, SDO, RESET, REXT SDR_EN, SPI_DIS DBGND DBGND ADGND Rating –0.3 V to 3.6 V –0.3 V to 2.8 V –0.3 V to +0.3 V –0.3 V to +0.3 V –0.3 V to AVDD1 + 0.3 V –1.0 V to AVDD1 + 0.3 V –0.3 V to CLKVDD + 0.3 V −0.3 V to DBVDD + 0.3 V –0.3 V to DBVDD + 0.3 V –0.3 V to ADVDD + 0.3 V 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. THERMAL RESISTANCE Thermal impedance can be lowered to 23°C/W by soldering the exposed package pad to an external heat sink (for example, the internal PCB copper ground plane). However, this is not necessary for the power dissipation and operating temperature range of the AD9726. Table 6. Thermal Resistance Package Type 80-Lead TQFP_EP Package, Thermally Enhanced ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. A | Page 7 of 24 θJA 32 Unit °C/W AD9726 SDR_EN ADVDD ADGND ACVDD ACGND AVDD2 AGND2 AVDD1 AGND1 IOUTB IOUTA AGND1 AVDD1 AGND2 AVDD2 ACGND ACVDD ADGND ADVDD SPI_DIS PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 CLKVDD 1 60 FSADJ 59 REFIO 3 58 RESET CLKGND 4 57 CSB CLK+ 5 56 SCLK (SYNCUPD) CLK– 6 55 SDIO CLKGND 7 54 SDO (SYNCALRM) DGND 8 53 DGND DVDD 9 52 DVDD DB15+ 10 51 DB0– DB15– 11 50 DB0+ DB14+ 12 49 DB1– DB14– 13 48 DB1+ DB13+ 14 47 DB2– DB13– 15 46 DB2+ DB12+ 16 45 DB3– DB12– 17 44 DB3+ DB11+ 18 43 DB4– DB11– 19 42 DB4+ DBVDD 20 41 DBGND REXT 2 CLKVDD PIN 1 AD9726 TOP VIEW (Not to Scale) 04540-005 DBVDD DB5– DB5+ DB6– DB6+ DB7– DB7+ DCLK_IN– DCLK_IN+ DBGND DBVDD DCLK_OUT– DCLK_OUT+ DB8– DB8+ DB9– DB9+ DB10– DB10+ DBGND 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Figure 5. Pin Configuration Table 7. Pin Function Descriptions Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Mnemonic CLKVDD REXT CLKVDD CLKGND CLK+ CLK− CLKGND DGND DVDD DB15+ DB15− DB14+ DB14− DB13+ DB13− DB12+ DB12− DB11+ DB11− DBVDD DBGND Description Clock Supply Voltage Sets Data Clock Output Drive1 Clock Supply Voltage Clock Supply Common DAC Clock Input True DAC Clock Input Complement Clock Supply Common Digital Supply Common Digital Supply Voltage Data Bit 15 True Data Bit 15 Complement Data Bit 14 True Data Bit 14 Complement Data Bit 13 True Data Bit 13 Complement Data Bit 12 True Data Bit 12 Complement Data Bit 11 True Data Bit 11 Complement Data Bus Supply Voltage Data Bus Supply Common Pin No. 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Rev. A | Page 8 of 24 Mnemonic DB10+ DB10− DB9+ DB9− DB8+ DB8− DCLK_OUT+ DCLK_OUT− DBVDD DBGND DCLK_IN+ DCLK_IN− DB7+ DB7− DB6+ DB6− DB5+ DB5− DBVDD DBGND DB4+ Description Data Bit 10 True Data Bit 10 Complement Data Bit 9 True Data Bit 9 Complement Data Bit 8 True Data Bit 8 Complement Data Clock Output True Data Clock Output Complement Data Bus Supply Voltage Data Bus Supply Common Data Clock Input True Data Clock Input Complement Data Bit 7 True Data Bit 7 Complement Data Bit 6 True Data Bit 6 Complement Data Bit 5 True Data Bit 5 Complement Data Bus Supply Voltage Data Bus Supply Common Data Bit 4 True AD9726 Pin No. 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Mnemonic DB4− DB3+ DB3− DB2+ DB2− DB1+ DB1− DB0+ DB0− DVDD DGND SDO (SYNCALRM) SDIO SCLK (SYNCUPD) CSB RESET REFIO FSADJ SDR_EN ADVDD ADGND ACVDD ACGND Description Data Bit 4 Complement Data Bit 3 True Data Bit 3 Complement Data Bit 2 True Data Bit 2 Complement Data Bit 1 True Data Bit 1 Complement Data Bit 0 True Data Bit 0 Complement Digital Supply Voltage Digital Supply Common SPI Data Output (SYNCALRM)2 SPI Data Input/Output3 SPI Clock Input (SYNCUPD)4 SPI Chip Select Bar (Active Low) Hardware Reset (Active High) Internal Reference Input/Output5 Output Current Full-Scale Adjust6 Single Data Rate Mode Enable7 Analog Supply Voltage Analog Supply Common Analog Supply Voltage Analog Supply Common Pin No. 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 1 Mnemonic AVDD2 AGND2 AVDD1 AGND1 IOUTB IOUTA AGND1 AVDD1 AGND2 AVDD2 ACGND ACVDD ADGND ADVDD SPI_DIS Description Analog Supply Voltage Analog Supply Common Analog Supply Voltage Analog Supply Common Analog Current Output Complement Analog Current Output True Analog Supply Common Analog Supply Voltage Analog Supply Common Analog Supply Voltage Analog Supply Common Analog Supply Voltage Analog Supply Common Analog Supply Voltage Serial Port Interface Disable8 Nominally 1 kΩ to DBGND (may be omitted if data clock output is unused). SDO is output in 4-wire SPI mode and three-state in 3-wire SPI mode. If SPI is disabled (SPI_DIS = ADVDD), alternate pin function is SYNCALRM output. 3 SDIO is input only in 4-wire SPI mode and bidirectional in 3-wire SPI mode. 4 If SPI is disabled (SPI_DIS = ADVDD), alternate pin function is SYNCUPD. 5 Bypass with 0.1 µF to AGND1. Use buffer amp to drive external circuitry. Limit output current to 1 µA. Apply external reference to this pin. 6 Nominally 2 kΩ to AGND1 for 20 mA full-scale output (internal reference). 7 If SPI is disabled, tie pin to ADVDD to enable SDR. Otherwise, tie to ADGND. 8 Tie pin to ADVDD to disable SPI; otherwise, tie to ADGND. 2 Rev. A | Page 9 of 24 AD9726 TERMINOLOGY Integral Nonlinearity (INL) The maximum deviation of the actual analog output from the ideal output, as determined by a straight line drawn from zero scale to full scale. Temperature Drift Temperature drift is specified as the maximum change in a parameter from ambient temperature (25°C) to either TMIN or TMAX and is typically reported as ppm/°C. Differential Nonlinearity (DNL) A measure of the maximum deviation in analog output associated with any single value change in the digital input code relative to an ideal LSB. Power Supply Rejection The maximum change in the full-scale output as all power supplies are varied over their respective operating voltage range. Offset Error The deviation of the output current from the ideal zero-scale current. For differential outputs, 0 mA is expected at IOUTA when all inputs are low, and 0 mA is expected at IOUTB when all inputs are high. Monotonicity A DAC is monotonic if the analog output increases or remains constant in response to an increase in the digital input. Gain Error The deviation of the output current from the ideal full-scale current. Actual full-scale output current is determined by subtracting the output when all inputs are low from the output when all inputs are high. Output Compliance Range The range of allowable voltage seen by the analog output of a current output DAC. Operation beyond the compliance limits may cause output stage saturation and/or breakdown resulting in nonlinear performance. Spurious-Free Dynamic Range (SFDR) The difference in decibels between the peak amplitude of a test tone and the peak amplitude of the largest spurious signal over the specified bandwidth. Intermodulation Distortion (IMD) The difference in decibels between the maximum peak amplitude of two test tones and the maximum peak amplitude of the distortion products created from the sum or difference of integer multiples of the test tones. Adjacent Channel Leakage Ratio (ACLR) The ratio between the measured power of a wideband signal within a channel relative to the measured power in an empty adjacent channel. Noise Spectral Density (NSD) The measured noise power over a 1 Hz bandwidth seen at the analog output. Total Harmonic Distortion (THD) The ratio in decibels of the rms power sum of the first six harmonic components to the rms power of the output signal. Rev. A | Page 10 of 24 AD9726 TYPICAL PERFORMANCE CHARACTERISTICS 100 630 620 POWER CONSUMPTION (mW) 90 80 –3dB 70 0dB 60 0 12 24 36 48 60 72 84 96 600 SDR 590 DDR 580 570 560 04540-007 50 610 04540-006 SFDR (dBc) –6dB 550 0 108 120 132 144 50 100 150 200 fOUT (MHz) fOUT (MHz) Figure 9. Power Consumption vs. fOUT @ 400 MSPS Figure 6. SFDR vs. fOUT @ 400 MSPS 100 0 REF LVL 0dBm RBW VBW SWT 1kHz 1kHz 17s RF ATT 40dB UNIT dBm A –10 90 –20 SFDR (dBc) –6dB –30 –40 80 1AVG 1AP –50 –3dB EXT –60 0dB 70 –70 –80 –90 60 50 0 12 24 36 48 60 04540-018 04540-008 –100 –110 –120 72 START 750kHz 675kHz STOP 7.5MHz fOUT (MHz) Figure 10. THD @ 400 MSPS and fOUT = 1 MHz (Diplexer Low-Pass Output Showing 0 dBm Fundamental; See Performance Effects of Calibration Section) Figure 7. SFDR vs. fOUT @ 200 MSPS 100 0 REF LVL 0dBm RBW VBW SWT 1kHz 1kHz 17s RF ATT 10dB UNIT dBm A –10 90 –20 –30 80 –40 1AVG 1AP –50 EXT –60 70 –70 –80 60 30 40 50 60 70 80 90 –100 –110 100 110 120 130 140 –120 START 750kHz fOUT (MHz) Figure 8. Two-Tone IMD vs. fOUT @ 400 MSPS 04540-019 50 20 –90 04540-009 IMD (dBc) f1 + f2 = 0dB 675kHz STOP 7.5MHz Figure 11. THD @ 400 MSPS and fOUT = 1 MHz (Diplexer High-Pass Output Showing Harmonics Before Calibration; See Performance Effects of Calibration Section) Rev. A | Page 11 of 24 AD9726 0 RBW VBW SWT REF LVL 0dBm 1kHz 1kHz 17s RF ATT 10dB UNIT REF –45dBm *AVG Log 10dB/ dBm A –10 *ATTEN 4dB –20 EXT REF –30 –40 1AP 1AVG –50 EXT –60 –70 –80 –90 PAVG 10 W1 S2 –110 –120 START 750kHz 675kHz CENTER 70.00MHz *RES BW 10kHz STOP 7.5MHz Figure 12. THD @ 400 MSPS and fOUT = 1 MHz (Diplexer High-Pass Output Showing Harmonics After Calibration, See Performance Effects of Calibration Section) REF –35dBm *AVG Log 10dB/ *ATTEN 8dB VBW 100kHz SPAN 59.58MHz SWEEP 1.739s (601 pts) TOTAL CARRIER POWER -20.62dBm/15.3600MHz RRC FILTER: ON FILTER ALPHA 0.22 REF CARRIER POWER -26.43dBm/3.84000MHz UPPER LOWER dBm dBc dBm OFFSET FREQ INTEG BW dBc 3.840MHz –66.59 –93.00 –67.07 –93.48 5.000MHz 1 –26.43dBm 3.840MHz –67.63 –94.04 –67.54 –93.95 10.00MHz 2 –26.53dBm 3.840MHz –67.59 –94.00 –67.44 –93.86 15.00MHz 3 –26.74dBm 4 –26.88dBm 04540-016 04540-020 –100 Figure 15. Four-Carrier WCDMA @ 400 MSPS fOUT = 70 MHz EXT REF REF –50dBm *AVG Log 10dB/ *ATTEN 2dB EXT REF PAVG 10 W1 S2 RMS RESULTS FREQ OFFSET CARRIER POWER 5.000MHz –14.58dBm/ 10.00MHz 3.84000MHz 15.00MHz REF BW 3.840MHz 3.840MHz 3.840MHz SPAN 34.68MHz SWEEP 1.012s (601 pts) LOWER dBc dBm –76.72 –91.30 –76.96 –91.54 –77.07 –91.65 UPPER dBc dBm –76.69 –91.27 –77.04 –91.62 –76.76 –91.34 Figure 13. One-Carrier WCDMA @ 400 MSPS fOUT = 70 MHz REF –40dBm *AVG Log 10dB/ PAVG 10 W1 S2 CENTER 70.00MHz *RES BW 10kHz VBW 100kHz SPAN 83.98MHz SWEEP 2.451s (601 pts) TOTAL CARRIER POWER -20.62dBm/15.3600MHz RRC FILTER: ON FILTER ALPHA 0.22 REF CARRIER POWER -26.43dBm/3.84000MHz UPPER LOWER dBm dBc dBm OFFSET FREQ INTEG BW dBc 3.840MHz –62.23 –94.82 –62.09 –94.68 5.000MHz 1 –32.21dBm 3.840MHz –62.87 –95.46 –62.36 –94.94 10.00MHz 2 –32.30dBm 3.840MHz –63.70 –96.28 –62.39 –94.98 15.00MHz 3 –32.44dBm 4 –32.59dBm *ATTEN 6dB EXT REF Figure 16. Eight-Carrier WCDMA @ 400 MSPS fOUT = 70 MHz PAVG 10 W1 S2 VBW 100kHz SPAN 47.38MHz SWEEP 1.383s (601 pts) TOTAL CARRIER POWER -17.61dBm/7.68000MHz RRC FILTER: ON FILTER ALPHA 0.22 REF CARRIER POWER -20.72dBm/3.84000MHz UPPER LOWER dBm dBm dBc OFFSET FREQ INTEG BW dBc 3.840MHz –70.61 –91.34 –70.74 –91.47 5.000MHz 1 –20.51dBm 3.840MHz –71.29 –92.01 –71.31 –92.03 10.00MHz 2 –20.72dBm 3.840MHz –71.36 –92.08 –71.06 –91.78 15.00MHz 04540-015 CENTER 70.00MHz *RES BW 10kHz Figure 14. Two-Carrier WCDMA @ 400 MSPS fOUT = 70 MHz Rev. A | Page 12 of 24 04540-017 VBW 100kHz 04540-014 CENTER 70.00MHz *RES BW 10kHz AD9726 SERIAL PORT INTERFACE Table 8. SPI Register Map Addr 0x00 0x02 0x0E 0x0F 0x10 0x11 0x15 0x16 Bit 7 SDIODIR DATAFMT Bit 6 DATADIR DATARATE SCALSTAT MEMADR[7] SELFCAL MEMADR[6] Bit 5 SWRESET INVDCLKI CALMEM[1] XFERSTAT MEMADR[5] MEMDAT[5] Bit 4 SLEEP INVDCLKO CALMEM[0] MEMXFER MEMADR[4] MEMDAT[4] Bit 3 PWRDWN DISDCLKO SYNCEXT SYNCIN[1] SYNCIN[0] SMEMWR MEMADR[3] MEMDAT[3] Bit 2 Bit 1 SYNCMAN CALCLK[2] SMEMRD MEMADR[2] MEMDAT[2] SYNCUPD CALCLK[1] FMEMRD MEMADR[1] MEMDAT[1] SYNCOUT[1] Bit 0 EXTREF SYNCALRM CALCLK[0] UNCAL MEMADR[0] MEMDAT[0] SYNCOUT[0] Table 9. SPI Register Bit Default and Descriptions Values Addr 0x00 0x02 0x0E 0x0F 0x10 Name SDIODIR Bit 7 I/O I Default 0 DATADIR 6 I 0 SWRESET SLEEP PWRDWN EXTREF DATAFMT 5 4 3 0 7 I I I I I 0 0 0 0 0 DATARATE 6 I 0 INVDCLKI INVDCLKO DISDCLKO SYNCMAN SYNCUPD SYNCALRM CALMEM 5 4 3 2 1 0 [5:4] I I I I I O O 0 0 0 0 0 0 00 CALCLK [2:0] I 000 SCALSTAT SELFCAL XFERSTAT MEMXFER SMEMWR SMEMRD FMEMRD UNCAL MEMADR 7 6 5 4 3 2 1 0 [7:0] O I O I I I I I I 0 0 0 0 0 0 0 0 00000000 Description 0: SDIO is input only (4-wire SPI mode), and SDO is used for output. 1: SDIO is input/output (3-wire SPI mode), and SDO is unused. 0: SPI serial data byte is MSB first format. 1: SPI serial data byte is LSB first format. 1: Software reset: SPI registers (except 0x00) to default values.1 1: Analog outputs temporarily disabled. 1: Full device power-down; all circuits disabled except SPI. 1: Power-down internal reference: use external reference source.2 0: Input data-word is twos complement binary format. 1: Input data-word is unsigned binary format. 0: DDR mode. 1: SDR mode. 1: Inverts polarity of data clock input. 1: Inverts polarity of data clock output. 1: Disables data clock output. 1: Enable sync manual mode; disable automatic update. 1: Force manual sync update. 1: Indicates that sync logic requires update. 2-bit SMEM contents and calibration status indicator. 00: Uncalibrated; SMEM contains default values (63). 01: Self-calibrated; SMEM contains values from self-calibration. 10: Factory-calibrated; SMEM values transferred from FMEM. 11: User-calibrated; SMEM contains user-entered values. 3-bit self-calibration clock divider ratio. Affects time available for algorithm settling. Each value increase reduces time by 50%.3 000: Self-calibration clock is DAC clock/4096 (maximum self-calibration settling time for highest linearity accuracy). 001,010,011: Self-calibration clock is DAC clock/2048,1024,512. 100,101,110: Self-calibration clock is DAC clock/256,128,64. 111: Self-calibration clock is DAC clock/32 (minimum self-calibration settling time for fastest algorithm completion). 1: Indicates completion of self-calibration cycle. 1: Initiates self-calibration cycle.4 1: Indicates completion of memory transfer cycle. 1: Initiates FMEM to SMEM transfer.5 1: Enable static memory (SMEM) write operation. 1: Enable static memory (SMEM) read operation. 1: Enable factory memory (FMEM) read operation. 1: Enable uncalibrated operation; all SMEM to default values.6 8-bit memory address value for read/write operations. Rev. A | Page 13 of 24 AD9726 Addr 0x11 0x15 0x16 Name MEMDAT SYNCOUT SYNCEXT SYNCIN Bit [5:0] [1:0] 5 [4:3] I/O I/O O I I Default 000000 00 0 00 Description 6-bit memory data value for read/write operations. 2-bit output value indicates current sync quadrant. 1: Enable sync external mode; disable auto quadrant select. 2-bit input value used to specify sync quadrant. 1 SWRESET also resets itself. SMEM contents are unaffected by SWRESET; however, CALMEM reports an uncalibrated state. EXTREF is optional because the internal reference circuit is designed to be overdriven by an external source. 3 The self-calibration clock is also used for the memory transfer cycle; therefore, the CALCLK value affects the MEMXFER process time. 4 Register Bits 3:0 must all be 0 to assert SELFCAL. The time required for the self-calibration cycle is ~100 ms at 100 MHz with CALCLK = 0. 5 Register Bits 3:0 must all be 0 to assert MEMXFER. The time required for the memory transfer cycle is ~15 ms at 100 MHz with CALCLK = 0. 6 The UNCAL bit remains asserted after the cycle completes (SMEM contents held at default values) until the bit is cleared by the user. 2 Rev. A | Page 14 of 24 AD9726 THEORY OF OPERATION The AD9726 uses LVDS for input data to enable high sample rates and high performance. LVDS technology uses differential signals for noise rejection and small signal amplitude for fast speed with lower power. Each LVDS input on the AD9726 has an internal 100 Ω active load for proper termination. VCC = CLKVDD = 2.5V 1:1 CLK+ 25Ω 25Ω VBB = 1.0V 50Ω DAC CLOCK AND DATA CLOCK OUTPUT 50Ω AD9726 VCC – 2V The AD9726 uses two clock inputs and offers one clock output. All are differential signals. The AD9726 is driven by a master input clock that initiates conversion and controls all on-chip activity. This signal is referred to as the DAC clock. It is not LVDS, and the CLK+ and CLK– pins are high impedance inputs. The DAC clock is then used to generate the data clock output. The DCLK_OUT+ and DCLK_OUT– pins form an LVDS signal that can be used to drive an external FPGA or another data pump. In SDR mode, the data clock output always runs at the same frequency as the DAC clock. In DDR mode, the data clock output always runs at ½ the DAC clock frequency. Use of the data clock output is optional. It is meant to serve as a convenient means of regulating the incoming data stream. The driver can be loaded by a 100 Ω differential termination. An external 1 kΩ resistor from the REXT pin to DBGND is also required to set the drive strength. If unused, the data clock output pins can be left unconnected and the 1 kΩ resistor at REXT can be omitted. 04540-012 CLK– MC100LVEP16 Figure 17. Active DAC Clock Drive Circuit The circuit option shown in Figure 17 uses a receiver/driver IC from the 2.5 V LVPECL logic family to provide complementary outputs that fall within these guidelines. A transformer helps ensure a 50% duty cycle and provides a single-ended to differential conversion at the input. The LVPECL device can be conveniently powered from the same power supply as CLKVDD. The center tap of the transformer secondary must be held at 1 V, the switching threshold of the receiver/driver inputs (use a resistive divider to generate this voltage or use the internal VBB source with a buffer amplifier). Based on a 1:1 impedance ratio, 25 Ω resistors across the secondary provide a matched load to a 50 Ω source. The driver outputs are terminated as close as possible to the AD9726 with 50 Ω to VCC − 2 V (or use a Thevenin equivalent circuit). Controlled impedance PCB traces should be used to minimize reflections. Signal levels at the CLK+ and CLK– pins transition between a high near 1500 mV to a low near 750 mV. The data clock output can also be inverted by asserting the INVDCLKO bit in SPI Register 0x02 or the driver can be disabled by asserting the DISDCLKO bit in the same register. 0.1µF CLK+ 1:1 50Ω DATA CLOCK INPUT The remaining clock signal associated with the AD9726 is the data clock input. This LVDS signal is not optional and must accompany the 16-bit data bus. The data clock input is used to latch incoming data into the synchronization (sync) logic. The data clock input always runs at the same frequency as the data clock output in both SDR and DDR modes. A logical inversion can be accomplished by asserting the INVDCLKI bit. Driving the DAC Clock Inputs The DAC clock must be precise and spectrally pure to ensure the highest ac performance. A symmetrical 50% duty cycle should be maintained at all times. The CLK+ and CLK– input pins should be driven by a signal with a common-mode voltage near ½ of CLKVDD. From this point, peak-to-peak signal amplitude should swing over a range of at least several hundred millivolts. VDC BIAS = 1.25V AD9726 04540-013 CLK– 0.1µF Figure 18. Passive DAC Clock Drive Circuit An alternative circuit option for driving the DAC clock inputs employs a transmission line transformer (balun) to accomplish the single-ended to differential conversion. This all-passive circuit is considerably simpler and less costly, and it provides acceptable performance over a limited range of frequencies. In this implementation, a sine wave (or other single-ended source) is coupled directly to the differential DAC clock inputs through a 50 Ω transformer. Capacitors are used for isolation, and each DAC clock pin must be dc-biased to a level of 1.25 V (a pair of simple resistive dividers can be used). Rev. A | Page 15 of 24 AD9726 DATA SYNCHRONIZATION CIRCUITRY The high performance of the AD9726 requires maintaining synchronization between the incoming bits and the DAC clock used to sample and convert the data. Despite the inherent difficulty in specifying the phase relationship of the DAC clock and the LVDS data clock input and the challenge presented by the high operating speed of the interface, the AD9726 contains real-time logic to automatically monitor and align the data bus with the DAC clock. Whether in SDR or DDR mode, input data is always provided at the same rate. Furthermore, the rate of incoming data always equals the frequency period of the DAC clock. The data rate and the DAC clock must also be frequency locked. To accomplish this, the primary purpose of the data clock output is to provide a time base for data that is derived directly from the DAC clock. The AD9726 is based around a high dynamic range CMOS core. The analog output consists of differential current sources, each capable of up to 20 mA full scale. Discrete output devices are PMOS and capable of sourcing current into an output termination within a compliance voltage range of ±1 V. In a typical application, both outputs drive discrete resistors-toanalog ground. From there, especially for higher frequency outputs, they feed the center-tap secondary of a 1:1 RF transformer. A differential-to-single-ended conversion is accomplished that provides added gain and cancellation of even ordered harmonics. IOUTA 25Ω IOUTB Figure 19. Transformer Output Circuit For maximum output power, resistor values can be increased to 50 Ω to provide up to 0 dBm into a 50 Ω load without loss of performance for most transformers. RGA The function of the data clock input is to latch incoming data into the sync block. From there, it is the function of the synchronization logic to position the data with respect to the DAC clock for optimal ac performance. More detailed explanations of sync operation and optional programmable modes are presented in the Sync Logic Operation and Programming section, which also includes an explanation of how to use the sync logic without the SPI. RFA IOUTA 50Ω RGB Individual data bits must maintain close alignment with one another so that PCB traces have matched delays across the width of the 16-bit bus. In addition, a fixed set-up and hold timing relationship between the data clock input and the data bus is required. However, because of the sync logic, the phase relationship between the data bus and the DAC clock is internally optimized. Furthermore, should the phase between the data bus and the DAC clock drift over time or temperature, the sync logic automatically updates and adjusts for it. Once synchronization has been reached, the phase between the data bus and the DAC clock can vary by a full cycle without loss or corruption of data. –3dBm 25Ω 04540-021 Good ac performance can be expected from either the active or passive DAC clock drive circuit. However, in a passive circuit, the output slew rate is dependent on the frequency of the input; whereas an active circuit provides consistently high output slew rates over a wide range of input frequencies. ANALOG OUTPUT RFB IOUTB 50Ω NOTES 1. USE RF AND RG TO SET GAIN AND LIMIT BANDWIDTH 04540-011 The 50 Ω termination resistor should be placed as close as possible to the input pins, and controlled impedance PCB traces should be used. Figure 20. Op Amp Output Circuit As an alternative, an active output stage can be used in the classic instrumentation amplifier configuration. Here, each DAC output feeds the noninverting input of one of Analog Devices’ high speed transimpedance op amps. INTERNAL REFERENCE AND FULL-SCALE OUTPUT The AD9726 contains an internal 1.2 V precision reference source; this reference voltage appears at the REFIO pin. It can be used to drive external circuitry if properly buffered. Apply an external reference voltage source to the REFIO pin if desired. The internal source is designed to be easily overdriven by an external source; however, the internal reference can also be powered down using the EXTREF bit in SPI Register 0x00. Rev. A | Page 16 of 24 AD9726 INSTRUCTION CYCLE DATA TRANSFER CYCLE CSB SCLK SDIO R/W N1 N0 A4 A3 A2 A1 SDO A0 D7n D6n D20 D10 D00 D7n D6n D20 D10 D00 04540-010 The reference voltage (either internal or external) is applied to an external precision resistor at the FSADJ pin. The resulting current is internally amplified to provide the full-scale current at the DAC output according to the following equation: IOUTFS = VREF/RFSADJ × 32 Figure 21. SPI Communication Cycle Taking into account the binary value appearing at the data bus inputs, the output currents IOUTA and IOUTB can be determined according to the following equations: IOUTA = IOUTFS × DB[15:0]/65536 IOUTB = IOUTFS × (1 − DB[15:0])/65536 Note that the AD9726 features nonvolatile, factory-calibrated gain using the internal reference source and a precision 2 kΩ load. Gain accuracy in any application is, therefore, dependent upon the accuracy of RFSADJ. Any communication cycle begins with CSB going low, which also resets the SPI control logic. Similarly, any communication cycle ends with CSB going high, which aborts any incomplete data transfer. Once a communication cycle begins, the next eight SCLK rising edges interpret data on the SDIO pin as the instruction byte. Instruction Byte The instruction byte bits are shown in the following bit map. B7 R/W RESET Following initial power up and application of a valid DAC clock signal, the AD9726 should always be initialized with an active high pulse on the RESET pin. This defaults the programmable registers, initializes volatile calibration memory, and prepares the synchronization logic for data. The data bus should be static prior to the reset pulse. After reset, LVDS data can flow. B6 N1 B5 N0 B4 A4 B3 A3 B2 A2 B1 A1 B0 A0 R/W Bit 7 of the instruction byte selects a read or write transfer. If the bit is set high, a read operation is indicated. If the bit is low, a write operation is indicated. N1, N0 The default state of the AD9726 is DDR and twos complement binary input data. To use the AD9726 in this mode, it is not necessary to program any device registers. However, the SPI is enabled by default unless the SPI_DIS pin is connected high. If not disabled, SPI input pins should not be left floating. SERIAL PORT INTERFACE The serial port interface is a flexible and synchronous serial communications port allowing easy interface to many industry standard microcontroller and microprocessor protocols (including both Motorola SPI® and Intel® SSR). The interface provides read/write access to registers that configure the operation of the AD9726. The AD9726 SPI supports single-byte and multibyte transfers as well as MSB- or LSB-justified data formats. The interface can be configured in 3-wire mode (in which SDIO is bidirectional) or the default 4-wire mode (in which SDIO and SDO function as unidirectional data input and data output, respectively). Communication Cycle All communication cycles have two phases. The first phase is concerned with writing an instruction byte into the SPI controller and always coincides with the first eight rising edges of SCLK. The instruction byte provides the controller with information regarding the second phase of the cycle, namely the data transfer phase. In the instruction byte, there are the number of data bytes to be transferred (1 to 4), a register address, and a bit initiating a read or write operation. Bit 6 and Bit 5 of the instruction byte determine the number of data bytes to be transferred, as shown in Table 10. Table 10. N1 0 0 1 1 N0 0 1 0 1 Description Transfer 1 data byte Transfer 2 data bytes Transfer 3 data bytes Transfer 4 data bytes A4, A3, A2, A1, A0 Bit 4 through Bit 0 of the instruction byte specify a 5-bit binary value corresponding to a valid register address. In the case of multibyte transfers, the location specified is either an initial or a concluding register address. The SPI controller increments or decrements this value to generate successive address values depending on whether LSB or MSB justification is active. MSB/LSB Transfers The SPI can support both MSB- and LSB-justified serial data byte formats. This functionality is determined by Bit 6 in SPI Register 0x00. This bit defaults low, which is MSB justification. In this mode, serial data bits are written to and/or read from registers sequentially from Bit 7 to Bit 0. If Bit 6 of SPI Register 0x00 is set high, the controller switches to LSB justification. In this mode, data bits are written to or read from registers sequentially from Bit 0 to Bit 7. Writing to the instruction bytes is also affected by the active justification. Rev. A | Page 17 of 24 AD9726 For multibyte transfers with MSB justification, the address in the instruction byte is interpreted as a final address, and its value is decremented automatically by the controller. For multibyte transfers with LSB justification, the address in the instruction byte is interpreted as an initial address, and its value is incremented automatically by the controller. Care must be exercised when switching from MSB to LSB justification. The controller switches modes immediately once all eight bits of SPI Register 0x00 are written (even if in the process of a multibyte transfer). For this reason, a single byte command is recommended when changing justification. 3-Wire and 4-Wire Operation Bit 7 of SPI Register 0x00 defaults low, enabling 4-wire SPI operation. In this mode, serial data is input from the SDIO pin, and serial data is output on the SDO pin. Setting Bit 7 of SPI Register 0x00 high enables 3-wire operation. In this mode, SDIO becomes bidirectional and switches automatically from input to output when necessary. The SDO pin in this mode is unused and assumes a high impedance state. As with MSB or LSB justification, care must be exercised when switching operational modes. The change occurs immediately once all eight bits of SPI Register 0x00 are written. Writing and Reading Register Data Bringing CSB low initiates a new communication cycle. The next eight rising edges of SCLK latch data from SDIO into the instruction byte. If Bit 7 of the instruction byte is low, a write operation is enabled. If Bit 7 is high, a read operation is enabled. For a write operation, a data byte is latched from the SDIO pin into a register on the next eight rising edges of SCLK. If the instruction byte Bit 6 and Bit 5 are not both 0, a multibyte transfer latches data bytes into adjacent registers after each successive set of eight rising SCLK edges. Depending upon MSB or LSB justification, the controller decrements or increments the address value in the instruction byte during the cycle as necessary. If a read operation is enabled, data bits from the register being addressed appear on SDO (or SDIO) with each falling edge of SCLK. Note that for a read operation, the eighth bit of the instruction byte is latched on the eighth rising edge of SCLK and the first output bit is enabled on the immediately following falling SCLK edge. For multibyte read sequences, the controller adjusts the register address when necessary and subsequent data bit values appear at the output with each falling SCLK edge. Disabling the SPI Tie the SPI_DIS pin high to ADVDD to disable the serial port interface. In this state, the default DDR operational mode can be changed to SDR by pulling the SDR_EN pin high to ADVDD. In addition, with the SPI disabled, the sync logic no longer operates in a fully automatic mode. See the Sync Logic Operation and Programming section for a full explanation of sync operational modes. SPI PIN DESCRIPTION The AD9726 SPI logic runs from the DBVDD supply rail, and input/output thresholds are based upon a nominal 3.3 V level. The maximum frequency of operation is 15 MHz. Chip Select (CSB) The CSB pin is an active low input. It begins and ends any communication cycle and must remain low during the entire cycle. An incomplete cycle is aborted if CSB is prematurely returned high . Serial Clock (SCLK) The SCLK pin is used to synchronize data to and from the SPI registers and the controller state machine runs from this input. It is therefore possible to read and write register data (but not SMEM/FMEM) without a valid DAC clock. All input data is registered on the rising edge of SCLK and output data bits are enabled on the falling edge of SCLK. Serial Data Input/Output (SDIO) Data is always written into the SPI on the SDIO pin. In 3-wire mode however, data is also driven out using this pin. The switch from input to output occurs automatically between the instruction and data transfer phases of a read operation. In the default 4-wire mode, SDIO is unidirectional and input only. Serial Data Output (SDO) Serial data is driven out on the SDO pin when the SPI is in its default 4-wire mode. In 3-wire mode (or whenever CSB is high) SDO is set to a high impedance state. CALIBRATION To ensure linearity to the 16-bit level, the AD9726 incorporates 132 calibration DACs (CALDACs), which are used to linearize the current output transfer function. Each CALDAC is a 6-bit device and takes its input directly from static memory (SMEM). There are 127 CALDACs associated with each major transition of the 16-bit input data-word (that is, any transition involving the upper 7 MSBs). A 128th CALDAC operates on the sum total of the lower 9 LSBs. The remaining 4 CALDACs (129 to 132) are used to adjust the DAC’s overall transfer function gain. Rev. A | Page 18 of 24 AD9726 Linearity CALDACs operate inversely from their input; that is, as their binary input value increases, the magnitude of their current contribution seen at the AD9726 output decreases. Gain CALDACs are an exception to this. Their contribution seen at the AD9726 output is in direct proportion to their binary input. Gain CALDACs are also half strength as compared to linearity CALDACs, but they are intended to be used together as a unit and thus provide twice the current adjustment range in sum total. Calibration Memory During production testing, the linearity of the AD9726 is measured and optimized. Values for all CALDACs are permanently stored in nonvolatile factory memory (FMEM). At reset, all factory memory contents are transferred to static memory. CALMEM indicates a factory calibrated state (CALMEM = 10b). CALMEM reports an uncalibrated state (CALMEM = 00b). Note that UNCAL remains asserted (and the contents of SMEM remains at default values) indefinitely. UNCAL does not clear itself (like SWRESET) and must be cleared by the user. Note also that although SPI registers do not depend on the DAC clock (they use SCLK to sequence the controller state machine), SMEM and/or FMEM access does require a valid DAC clock. SMEM/FMEM Read/Write Procedures Static and factory memory is accessed through the SPI, but it is not part of the SPI logic. For this reason, memory access requires a valid DAC clock, while SPI register access does not. Because the AD9726 SPI is so flexible, allowing single and multiple byte reads and writes as well as MSB or LSB justified data, there are perhaps a number of ways in which a user can access one or more SMEM or FMEM locations. It is also possible at any time to transfer the contents of FMEM to SMEM by asserting the MEMXFER bit. The XFERSTAT indicator bit then reports the successful completion of the transfer cycle, and MEMXFER is cleared. To avoid potential errors, the following procedures for accessing static or factory memory should be followed. These procedures use only single-byte SPI commands to ensure the enabling of addresses and the sequencing of memory access. Note that the MEMXFER bit (and SELFCAL) cannot be asserted if any other memory access function is currently enabled (that is, if any Bit [3:0] of Register 0x0F is high). Attempting to assert MEMXFER (or SELFCAL) in this case clears any asserted bits in Register 0x0F, but the requested cycle does not commence. To read from SMEM or FMEM, The factory-to-static memory data transfer cycle requires a number of DAC clock cycles. The total depends on the value of CALCLK. This value sets a divider used to create a slow version of the DAC clock, which is intended to extend the settling time available to the self-calibration cycle. However, this divided clock is also used to sequence a memory transfer cycle. The divider is set to its maximum value with CALCLK at its default value. A memory transfer cycle requires about 15 ms at a DAC clock frequency of 100 MHz. This time can be reduced by 50% for every increase in the value of CALCLK. 1. Ensure that Bits [3:0] of Register 0x0F are clear. 2. Begin the sequence by writing the memory address value to Register 0x10 with a single-byte SPI write command. 3. Assert the SMEMRD or FMEMRD bit in Register 0x0F with another single-byte SPI write command. 4. Import the contents of Register 0x11 using a single-byte SPI read command. 5. Clear the SMEMRD or FMEMRD bit with another singlebyte command. To write to SMEM, 1. Ensure that Bits [3:0] of Register 0x0F are clear. 2. Begin the sequence by writing the data value to Register 0x11 using a single-byte SPI write command. 3. Assert the SMEMWR bit using a single-byte SPI write command. 4. Place the memory address value in Register 0x10 using a single-byte SPI write command. 5. Clear the SMEMWR bit with a fourth single-byte SPI write command. Accessing Calibration Memory SMEM or FMEM locations can be read at any time by setting the SMEMRD or FMEMRD bit in SPI Register 0x0F. Address and data information can be input and/or output through SPI Register 0x10 and SPI Register 0x11, respectively. SMEM locations can also be written by setting the SMEMWR bit. Register 0x10 and Register 0x11 are again used for addresses and data. Any time after the SMEMWR bit has been asserted, the device reports a user-calibrated state (CALMEM = 11b) until another action changes the calibration memory status. To reset static memory at any time, assert the UNCAL bit. All SMEM locations are then reset to their default values (63). Rev. A | Page 19 of 24 AD9726 Self Calibration The AD9726 features an internal self-calibration engine to linearize the transfer function automatically. This can be very useful at temperature extremes where factory calibration no longer applies. The automated cycle can be initiated by asserting the SELFCAL bit. The self-calibration process calibrates all linearity and gain CALDACs based upon a fixed internal reference current. Values for all CALDACs are stored in volatile static memory. The CALSTAT bit indicates the successful completion of the cycle, and the SELFCAL bit is cleared. Following the cycle, the device reports a self-calibrated state (CALMEM = 01b). As with MEMXFER, successful assertion of the SELFCAL bit requires that Bits [3:0] of Register 0x0F be clear. If any of these bits are asserted (such that an SMEM/FMEM read/write/clear state is enabled), the self-calibration cycle does not begin. The time required to self-calibrate is dependent on both the DAC clock frequency and the value of CALCLK. Because selfcalibration requires more time than ordinary operation, the DAC clock is divided into a slower version and used to step through the process. Time made available to the self-calibration algorithm directly impacts its ability to provide accurate results. A maximum fixed division ratio (4096) corresponds to the minimum default value of CALCLK (0). The division ratio can be decreased by increasing the value of CALCLK. Each increase in the value of CALCLK reduces the DAC clock division factor (and, therefore, the time made available to self-calibration) by 50%. With CALCLK at its maximum value (7), the divide ratio declines to its minimum value (32). With CALCLK at its default value, self-calibration requires approximately 100 ms at a DAC clock frequency of 100 MHz. This time can be reduced to under 0.8 ms if CALCLK = 7. Time scales relative to DAC clock frequency. Performance Effects of Calibration Harmonic distortion for low frequency outputs is primarily a function of DAC linearity. Figure 10 to Figure 12 show the harmonic distortion performance of the AD9726. Figure 10 shows a 1 MHz full-scale output tone. The output drives a unique low-pass and high-pass filter called a diplexer. This type of filter presents a uniform 50 Ω load to the DAC and splits the output signal into low and high frequency paths. The diplexer's low-pass output passes the 1 MHz fundamental but attenuates higher frequencies, and the diplexer's high-pass output passes higher frequencies and attenuates the 1 MHz fundamental. Figure 10 also shows the diplexer's low-pass output. Here the noise floor is higher than the harmonic distortion because with a high power input signal, attenuation is required by the spectrum analyzer. Figure 11 shows the diplexer's high pass output where the attenuated input signal can be seen. The spectrum analyzer attenuation has also been reduced, which lowers the noise floor. Harmonic products at integer multiples of the fundamental are thus revealed. This is the response using the AD9726 in an uncalibrated state. Figure 12 shows a response using the AD9726 in a calibrated state. Harmonic distortion due to the nonlinearities of the digital-to-analog conversion have been virtually eliminated. SYNC LOGIC OPERATION AND PROGRAMMING Recall that a fixed set-up and hold timing relationship between the data clock input and the data bus must be established and maintained. Recall also that the data bus and the DAC clock must be frequency locked. Because of the sync logic, however, the phase relationship between the data bus and the DAC clock is internally optimized. Therefore, data arrival propagation delays and concern about data transitions near the sampling instant are eliminated. Synchronization is automatically enabled upon reset. Once data arrives and synchronization has been achieved, the sync logic continuously monitors itself so that automatic adjustments are made if phase drifts occur over time and/or temperature, automatic adjustments are made. Note that the sync function and operation of the sync logic block are transparent, automatic, and ongoing. No programming is required. For applications where it is useful, however, the following programmable control is provided. SYNC Operating States The sync logic can operate in one of three possible modes. The default mode is fully automatic. Fully automatic synchronization is accomplished by demultiplexing the incoming data stream into four channels, each containing every fourth data-word. Data-words are present for four DAC clock cycles. Data is remultiplexed by sampling each channel with the optimum DAC clock cycle. Initial synchronization is first established through a hardware reset. This also fully enables the synchronization logic to monitor and resynchronize, as necessary. The AD9726 resynchronizes only if conditions change enough to alter the phase between the data bus and the DAC clock by more than one full clock cycle. In this event, an internal alarm occurs and is followed by an automatic update. During resynchronization, two data-words are typically lost or repeated. In addition to fully automatic mode, two semi-automatic modes are available. Rev. A | Page 20 of 24 AD9726 Sync Manual Mode SYNC External Mode In fully automatic mode, the AD9726 both detects when a resynchronization is necessary and initiates an update. In manual mode, automatic updating is disabled. Enable manual mode by setting the SYNCMAN bit in SPI Register 0x02. Going beyond manual mode, sync external mode offers a greater level of control and can be useful if multiple DAC channels are employed in an application. Enable sync external mode by asserting the SYNCEXT bit in SPI Register 0x16. Manual mode must also be enabled. In manual mode, the sync logic still monitors incoming data and the DAC clock, but it indicates the need for an update by asserting the SYNCALRM bit. In this mode, the user is expected to regularly poll the SYNCALRM bit. When this bit is read back high, the user can issue a manual sync update also by asserting the SYNCUPD bit in SPI Register 0x02. SYNCALRM does not indicate that data is being lost but that conditions are close to the point where data may be lost. The sync logic should be resynchronized by asserting SYNCUPD at the next convenient time. In manual mode, users can choose when to update the sync logic. When operating with burst data, issuing a sync update between active bursts updates the system without risking the loss of any data. In fact, because SYNCUPD always forces a resynchronization regardless of operational mode, even users in fully automatic mode can reduce the possibility of data loss by occasionally forcing a sync update during idle activity. If either the data clock or the DAC clock is interrupted for any reason, a SYNCUPD should always be executed to ensure that data bus and DAC clock phase alignment remains optimized. The four channels into which each incoming data-word is multiplexed are called quadrants. In any mode, the current quadrant value can always be read back via SYNCOUT (Bits [1:0] of SPI Register 0x15). At sync update, the logic chooses the optimal quadrant and refreshes the value of SYNCOUT. It is also possible to enter a value into SYNCIN (Bits [4:3] of SPI Register 0x16). When external mode is enabled, the logic operates as expected, except that the quadrant value in SYNCIN is used following an update. This can be used to align delays between multiple device outputs. Operating With SPI Disabled If the SPI_DIS pin is connected high to ADVDD and the SPI is disabled, the sync logic is placed into manual mode. SYNCALRM status can then be monitored in hardware via the unused SPI pin SDO (54), and SYNCUPD requests can be entered in hardware via the unused SPI pin SCLK (56). If these two pins are connected together, fully automatic sync operation can be achieved. Rev. A | Page 21 of 24 AD9726 OUTLINE DIMENSIONS 14.20 14.00 SQ 13.80 0.75 0.60 0.45 1.20 MAX 12.20 12.00 SQ 11.80 80 61 61 1 60 80 1 60 PIN 1 EXPOSED PAD TOP VIEW (PINS DOWN) BOTTOM VIEW 0° MIN 1.05 1.00 0.95 0.15 0.05 SEATING PLANE 6.00 BSC SQ 0.20 0.09 7° 3.5° 0° 0.08 MAX COPLANARITY (PINS UP) 20 41 40 21 VIEW A 41 20 21 40 0.50 BSC LEAD PITCH 0.27 0.22 0.17 VIEW A ROTATED 90° CCW COMPLIANT TO JEDEC STANDARDS MS-026-ADD-HD Figure 22. 80-Lead Thin Plastic Quad Flat Package, Exposed Pad [TQFP_EP] (SV-80-1) Dimensions shown in millimeters ORDERING GUIDE Model AD9726BSVZ1 AD9726BSVZRL1 AD9726-EB 1 Temperature Range −40°C to +85°C −40°C to +85°C Package Description 80-Lead TQFP_EP 80-Lead TQFP_EP Evaluation Board Z = Pb-free part. Rev. A | Page 22 of 24 Package Option SV-80-1 SV-80-1 AD9726 NOTES Rev. A | Page 23 of 24 AD9726 NOTES © 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04540-0-11/05(A) Rev. A | Page 24 of 24