SPT7852 DUAL 10-BIT, 20 MSPS, 160 mW A/D CONVERTER FEATURES APPLICATIONS • • • • • • • • • • • • Dual 10-Bit/20 MSPS Analog-to-Digital Converter Monolithic CMOS Internal Track-and-Hold Low Power Dissipation: 160 mW 4 Vp-p Analog Input Range for Each ADC Single +5 Volt Power Supply with Option for 3.3 V Digital Outputs • Tri-State, TTL-Compatible Outputs • Overrange Bit • Selectable Two’s Complement or Straight Binary Output Video Set-Top Boxes Cellular Base Stations QPSK/QAM RF Demodulation S-Video Digitizers Composite Video Digitizers Portable and Handheld Instrumentation GENERAL DESCRIPTION The SPT7852 has two 10-Bit CMOS analog-to-digital converters that can sample data at speeds up to 20 MSPS. It has excellent low noise performance with a very low typical power dissipation of only 160 mW—that’s the total power for both converters. The SPT7852 uses a dual configuration of the proprietary circuit design found in our 10-bit CMOS single converter family, to achieve its high performance in a CMOS process. The SPT7852 is specifically designed for video decoding applications and is ideal for S-video decoding and decoding of multiple composite video sources. It also has excellent application in the area of coherent I/Q demodulation in such applications as QAM demodulation and TV set-top box converters. Inputs and outputs are TTL/CMOS-compatible to interface with TTL/CMOS-logic systems. Output data format is selectable for either straight binary or two’s complement. The SPT7852 is available in a 44L TQFP package in commercial and industrial temperature ranges. It is also available in die form. For availability of extended temperature ranges, please contact the factory. BLOCK DIAGRAM MSB Invert 10 VINA T/H Clock Reset Output Enable Overrange DA0-9 Reference Ladder Reference In VINB Output Buffer ADCA T/H ADCB Timing Generation 10 Output Buffer Overrange DB0-9 ABSOLUTE MAXIMUM RATINGS (Beyond which damage may occur)1 25 °C Supply Voltages AVDD ......................................................................... +6 V DVDD ......................................................................... +6 V Output Digital Outputs ....................................................... 10 mA Temperature Operating Temperature ................................... 0 to 70 °C Junction Temperature ........................................... 175 °C Lead Temperature, (soldering 10 seconds) .......... 300 °C Storage Temperature ............................... –65 to +150 °C Input Voltages Analog Input ................................. –0.5 V to AVDD +0.5 V VRef .............................................. –1.5 V to AVDD +0.8 V CLK Input ................................................................... VDD AVDD – DVDD ...................................................... ±100 mV Note: 1. Operation at any Absolute Maximum Rating is not implied. See Electrical Specifications for proper nominal applied conditions in typical applications. ELECTRICAL SPECIFICATIONS FOR EACH CHANNEL TA = TMIN to TMAX, AVDD = DVDD = +5.0 V, VIN =0 to 4 V, ƒS =20 MSPS, ƒCLK =40 MHz, VRHS =4.0 V, VRLS =0.0 V, unless otherwise specified. PARAMETERS TEST CONDITIONS TEST LEVEL Resolution MIN TYP MAX 10 Bits DC Accuracy Integral Nonlinearity Differential Nonlinearity IV IV Analog Input Input Voltage Range Input Resistance Input Capacitance Input Bandwidth Offset Gain Error V V V V VI VI VRLS 50 VI 350 425 500 IV IV V V V 0 3.0 1.0 4.0 150 150 2.0 AVDD 5.0 Conversion Characteristics Maximum Conversion Rate1 Minimum Conversion Rate1 Pipeline Delay (Latency) Aperture Delay Time Aperture Jitter Time VI IV IV V V 20 Dynamic Performance Effective Number of Bits ƒIN=3.58 MHz ƒIN= 10 MHz VI VI 8.4 7.9 Reference Input Resistance Voltage Range VRLS VRHS VRHS – VRLS ∆(VRHF – VRHS) ∆(VRLS – VRLF) 12X Full Power VRHS – VRLS UNITS ±1.0 ±1.0 LSB LSB VRHS 5.0 35 ±2.0 ±2.0 V kΩ pF MHz LSB LSB Ω V V V mV mV 5 15 MHz kHz Clock Cycles ns ps 8.9 8.4 Bits Bits 100 12 Clock required. SPT7852 2 1/12/00 ELECTRICAL SPECIFICATIONS TA=TMIN to TMAX, AVDD = DVDD = +5.0 V, VIN =0 to 4 V, ƒS =20 MSPS, ƒCLK =40 MHz, VRHS = 4.0 V, VRLS =0.0 V, unless otherwise specified. PARAMETERS TEST CONDITIONS TEST LEVEL MIN TYP VI VI 53 52 57 56 dB dB dB dB Dynamic Performance Signal-to-Noise Ratio (without Harmonics) ƒIN=3.58 MHz ƒIN=10 MHz Harmonic Distortion ƒIN=3.58 MHz ƒIN=10 MHz Signal-to-Noise and Distortion (SINAD) ƒIN=3.58 MHz ƒIN=10 MHz Channel-to-Channel Crosstalk ƒIN=3.58 MHz Channel-to-Channel Gain Matching Full Scale Spurious Free Dynamic Range ƒIN=3.58 MHz @ –3 dB FS Differential Phase Differential Gain VI VI 56 52 59 54 VI VI IV IV V V V 52 49 55 52 70 0.04 66 0.2 0.3 Digital Inputs Logic "1" Voltage Logic "0" Voltage Maximum Input Current Low Maximum Input Current High Input Capacitance VI VI VI VI V 2.0 Digital Outputs Logic "1" Voltage Logic "0" Voltage tRISE/tFALL Output Enable to Data Output Delay Power Supply Requirements Voltages DVDD AVDD OVDD Currents AIDD DIDD Power Dissipation VIL=0 V VIH=5 V IOH=0.5 mA IOS=1.6 mA 15 pF Load 20 pF Load, TA=+25 °C 50 pF Load Over Temp. Total for Both Converter Channels TEST LEVEL CODES All electrical characteristics are subject to the following conditions: All parameters having min/max specifications are guaranteed. The Test Level column indicates the specific device testing actually performed during production and Quality Assurance inspection. Any blank section in the data column indicates that the specification is not tested at the specified condition. TEST LEVEL MAX dB dB dB dB dB Degree % 0.8 +10 +10 –10 –10 5 VI VI V V V OVDD–0.5 IV IV IV VI VI VI 4.75 4.75 2.7 0.4 10 10 22 5.0 5.0 5.0 15 17 160 UNITS 5.25 5.25 5.25 18 20 190 V V µA µA pF V V ns ns ns V V V mA mA mW TEST PROCEDURE I 100% production tested at the specified temperature. II 100% production tested at TA=+25 °C, and sample tested at the specified temperatures. III QA sample tested only at the specified temperatures. IV Parameter is guaranteed (but not tested) by design and characterization data. V Parameter is a typical value for information purposes only. VI 100% production tested at TA = +25 °C. Parameter is guaranteed over specified temperature range. SPT7852 3 1/12/00 Figure 1 –Typical Interface Circuit +A5 +A5 Ref In (+4 V) MSBINV 3-st EN EN Reset VRHF 11 Digital Output A VRHS VRLS VRLF DAV SPT7852 Interfacing Logic VCAL VIN1 VINA VIN2 VINB Clock CLK 11 Digital Output B AVDD DVDD GND .1 µF OVDD .1 µF FB * 4.7 µF 4.7 µF +A5 1. 2. 3. 4. FB * 3.3 V/5 V Place the ferrite bead (*) as close to the ADC as possible. Place 0.1 µF decoupling capacitors as close to the ADC as possible. All capacitors are 0.1 µF surface-mount unless otherwise specified. All analog input pins (references, analog input, clock input) must be protected. (See absolute maximum ratings.) TYPICAL INTERFACE CIRCUIT POWER SUPPLIES AND GROUNDING Very few external components are required to achieve the stated device performance. Figure 1 shows the typical interface requirements when using the SPT7852 in normal circuit operation. The following sections provide descriptions of the major functions and outline critical performance criteria to consider for achieving the optimal device performance. CADEKA suggests that both the digital and the analog supply voltages on the SPT7852 be derived from a single analog supply as shown in figure 1. A separate digital supply must be used for all interface circuitry. CADEKA suggests using this power supply configuration to prevent a possible latch-up condition on powerup. SPT7852 4 1/12/00 The 16-phase clock, which is derived from the input clock, synchronizes these events. The timing signals for adjacent ADC sections are shifted by two clock cycles so that the analog input is sampled on every other cycle of the input clock by exactly one ADC section. After 16 clock periods, the timing cycle repeats. The sample rate for the configuration is one-half of the clock rate, e.g., for a 40 MHz clock rate, the input sample rate is 20 MHz. The latency from analog input sample to the corresponding digital output is 12 clock cycles. OPERATING DESCRIPTION The general architecture for the CMOS ADC is shown in the block diagram. The design contains two sets of eight identical successive approximation ADC sections, all operating in parallel, a 16-phase clock generator, an 11-bit 8:1 digital output multiplexer, correction logic, and a voltage reference generator which provides common reference levels for each ADC section. The high sample rate is achieved by using multiple SAR ADC sections in parallel, each of which samples the input signal in sequence. Each ADC uses 16 clock cycles to complete a conversion. The clock cycles are allocated as follows: • Since only sixteen comparators are used, a huge power savings is realized. • The auto-zero operation is done using a closed loop system that uses multiple samples of the comparator's response to a reference zero. Table I – Clock Cycles Clock Operation 1 Reference zero sampling 2 Auto-zero comparison 3 Auto-calibrate comparison 4 Input sample 5–15 11-bit SAR conversion 16 Data transfer • The auto-calibrate operation, which calibrates the gain of the MSB reference and the LSB reference, is also done with a closed loop system. Multiple samples of the gain error are integrated to produce a calibration voltage for each ADC section. • Capacitive displacement currents, which can induce sampling error, are minimized since only one comparator per VIN input samples the input during a clock cycle. • The total input capacitance is very low since sections of the converter which are not sampling the signal are isolated from the input by transmission gates. SPT7852 5 1/12/00 Figure 2 – Timing Diagram 1 tC tCLK 2 Clock Reset td 1 Data Valid (DAV) Data Output (Channel A) Data Output (Channel B) tSet 3 tHold tOD Invalid 4 Invalid Invalid Invalid Invalid tOD Invalid Notes: 1) Data Valid is forced low on Reset = High. 2) Data updated on first rising edge of clock after Reset goes low. 3) Data Valid rising edge will occur on the second rising edge of Clock after Reset goes low. Use the rising edge of Data Valid to latch the ADC output data. 4) Analog Input Data is sampled during the first clock cycle after Reset goes low. Valid data output from this sample will be available 12 clock cycles later (6 Data Valid cycles). All data during the 12 clock cycle latency is invalid. The reset pin is low for normal device operation. When reset is brought high, Data Valid (DAV) is immediately forced low and data output updates are suspended. Operation will resume on the first rising edge of the clock after the reset pin has been brought low. The first Data Valid rising edge will occur on the second edge of the clock after the reset goes low. CLOCK INPUT The SPT7852 is driven from a single-ended TTL-input clock. Because the pipelined architecture operates on the rising edge of the clock input, the device can operate over a wide range of input clock duty cycles without degrading the dynamic performance. The device's sample rate is 1/2 of the input clock frequency. (See timing diagram.) The first analog input sample will be taken during the first clock cycle after reset goes low. Valid data from this sample will be available 12 clock cycles later. All data during this 12 cycle latency will be invalid (Refer to figure 3, Timing Diagram 2.) TIMING AND RESET FUNCTION The two on-board ADCs in the SPT7852 are driven off of a single external TTL clock. This external clock must be 2X the desired sample rate. In applications that require a known phase relationship between the clock, analog input sampling and valid data output, a reset function is provided to establish a known phase relationship. (Because of the 2X clock, an exact phase relationship will not be known otherwise.) Refer to figure 2, Timing Diagram 1. SPT7852 6 1/12/00 Figure 3 – Timing Diagram 2 1 Analog In (Channel A) 5 2 3 6 7 4 8 11 10 9 Analog In (Channel B) Clock In Reset Sampling Clock (Internal) Invalid Data Out (Channel A) Valid 1 Invalid Data Out (Channel B) 2 3 4 3 4 Valid 1 2 Data Valid Table II – Timing Parameters Table DESCRIPTION PARAMETERS Conversion Time Clock Period Clock Duty Cycle Output Delay (15 pF Load) DAV Pulse Width Clock to DAV Data Set Up Time Data Hold Time tc tCLK tOD tDAV td tSet tHold MIN 2*tCLK 25 40 TYP 50 11 tCLK 15 MAX UNITS 60 ns ns % ns ns ns 22 28 SPT7852 7 1/12/00 Figure 5 – Simplified Reference Ladder Drive Circuit Without Force/Sense Circuit Figure 4 – Ladder Force/Sense Circuit + - 1 2 +4.0 V External Reference VRHF 150 mV VRHS (+3.85 V) VRHS R/2 R R 3 VRLS R R=30 Ω (typ) All capacitors are 0.01 µF R + 4 R VRLF R 5 VRLS AGND (0.150 V) 150 mV R/2 VRLF (AGND) 0.0 V All capacitors are 0.01 µF tied to AGND. A 150 mV drop is seen at VRHS (= 3.85 V) and a 150 mV increase is seen at VRLS (= 0.150 V). VOLTAGE REFERENCE The SPT7852 requires the use of a single external voltage reference for driving the high side of the reference ladder. It must be within the range of 3 V to 5 V. Both ADCs share the same reference ladder. The lower side of the ladder is typically tied to AGND (0.0 V), but can be run up to 2.0 V with a second reference. The analog input voltage range will track the total voltage difference measured between the ladder sense lines, VRHS and VRLS. ANALOG INPUT VINA and VINB are the analog inputs for channel A and channel B, respectively. Both channels share the same reference ladder. The input voltage range is from VRLS to VRHS (typically 4.0 V) and will scale proportionally with respect to the voltage reference. (See voltage reference section.) Force and sense taps are provided to ensure accurate and stable setting of the upper and lower ladder sense line voltages across part-to-part and temperature variations. By using the configuration shown in figure 4, offset and gain errors of less than ±2 LSB can be obtained. The drive requirements for the analog inputs are very minimal when compared to most other converters due to the SPT7852’s extremely low input capacitance of only 5 pF and very high input resistance of 50 kΩ. The analog input should be protected through a series resistor and diode clamping circuit as shown in figure 6. In cases where wider variations in offset and gain can be tolerated, VRef can be tied directly to VRHF and AGND can be tied directly to VRLF as shown in figure 5. Decouple force and sense lines to AGND with a .01 µF capacitor (chip cap preferred) to minimize high-frequency noise injection. If this simplified configuration is used, the following considerations should be taken into account: Figure 6 – Recommended Input Protection Circuit +V The reference ladder circuit shown in figure 5 is a simplified representation of the actual reference ladder with force and sense taps shown. Typically, the top side voltage drop for VRHF to VRHS will equal: AVDD D1 Buffer VRHF – VRHS = 3.75% of (VRHF – VRLF) (typical), ADC 47 Ω D2 and the bottom side voltage drop for VRLS to VRLF will equal: VRLS – VRLF = 3.75% of (VRHF – VRLF) (typical). -V Figure 5 shows an example of expected voltage drops for a specific case. VRef of 4.0 V is applied to VRHF and VRLF is D1 = D2 = Hewlett Packard HP5712 or equivalent SPT7852 8 1/12/00 CALIBRATION POWER SUPPLY SEQUENCING CONSIDERATIONS The SPT7852 uses an auto-calibration scheme to ensure 10-bit accuracy over time and temperature. Gain and offset errors are continually adjusted to 10-bit accuracy during device operation. This process is completely transparent to the user. All logic inputs should be held low until power to the device has settled to the specific tolerances. Avoid power decoupling networks with large time constants which could delay VDD power to the device. Upon powerup, the SPT7852 begins its calibration algorithm. In order to achieve the calibration accuracy required, the offset and gain adjustment step size is a fraction of a 10bit LSB. Since the calibration algorithm is an oversampling process, a minimum of 10k clock cycles are required. This results in a minimum calibration time upon powerup of 250 µsec (for a 20 MHz sample rate). Once calibrated, the SPT7852 remains calibrated over time and temperature. DIGITAL OUTPUTS, DATA VALID, AND MSB INVERT The output data for both channels can be latched using the rising edge of Data Valid (DAV). Refer to table II for minimum data setup and hold times. The format of the data is straight binary when the MSB Invert pin (MSBINV) is held low and Two’s Complement format when MSB Invert is high. Since the calibration cycles are initiated on the rising edge of the clock, the clock must be continuously applied for the SPT7852 to remain in calibration. OVERRANGE OUTPUT An OVERRANGE OUTPUT from D10A or D10B is an indication that the analog input signal has exceeded the positive full-scale input voltage by 1 LSB. When this condition occurs, D10A/B will switch to logic 1. All other data outputs (D0A/B to D9A/B) will remain at logic 1 as long as D10A/B remains at logic 1. This feature makes it possible to include the SPT7852 in higher resolution systems. INPUT PROTECTION All I/O pads are protected with an on-chip protection circuit shown in figure 7. This circuit provides ESD robustness to 3.5 kV and prevents latch-up under severe discharge conditions without degrading analog transition times. Figure 7 – On-Chip Protection Circuit Table III – Output Data Information (Binary Code) VDD 120 Ω Output Code Output Code Overrange (MSBINV=0) (MSBINV=1) Analog Input D10A/B D9A/B–D0A/B D9A/B–D0A/B +FS + 1/2 LSB 1 11 1 1 1 1 1111 01 1 1 1 1 1 1 1 1 +FS – 1/2 LSB 0 1 1 1 1 1 1 1 1 1 Ø 01 1 1 1 1 1 1 1 Ø [+FS –(–FS)]/2 0 ØØ ØØØØ ØØØØ ØØ ØØØØ ØØØØ –FS + 1/2 LSB 0 00 0000 000Ø 10 0000 000Ø –FS 0 00 0000 0000 10 0000 0000 Ø indicates the flickering bit between logic 0 and 1. +FS = VRHS; –FS = VRLS Analog 120 Ω Pad SPT7852 9 1/12/00 PACKAGE OUTLINE 44-LEAD TQFP A INCHES B SYMBOL Pin 1 Index C E D MIN MILLIMETERS MAX MIN MAX A 0.472 Typ 12.00 Typ B 0.394 Typ 10.00 Typ C 0.394 Typ 10.00 Typ D 0.472 Typ 12.00 Typ E 0.031 Typ F 0.012 0.017 0.300 0.45 G 0.035 0.040 0.85 1.05 H 0.002 0.006 0.05 0.15 0.030 0.450 0.750 0.80 Typ I 0.018 J 0.039 Typ 1.00 Typ K 0-7° 0-7° F G K I H J SPT7852 10 1/12/00 PIN FUNCTIONS PIN ASSIGNMENTS 37 36 35 D7A 38 34 D8A 39 D5A D9A 40 D6A EN D10A 41 43 42 44 GND DVDD OVDD AVDD VRHF 1 33 D4A VRHS 2 32 D3A VRLS 3 31 D2A VRLF 4 30 D1A GND 5 29 D0A 28 DAV NAME VRHF VRHS VRLS VRLF VCAL VINA VINB AVDD DVDD OVDD GND CLK VINA 6 GND 7 27 D0B VINB 8 26 D1B MSBINV 9 25 D2B Reset 10 24 D3B EN VCAL 11 23 D4B D0A – D9A TOP VIEW 21 22 20 19 18 17 16 15 14 13 12 D0B – D9B D5B D7B D6B D8B D9B CLK D10B GND OVDD DVDD AVDD D10A D10B DAV MSBINV Reset FUNCTION Reference High Force Reference High Sense Reference Low Sense Reference Low Force Calibration Reference Channel A Analog Input Channel B Analog Input Analog Power Supply Digital Power Supply Digital Output Supply (3.3 V/5 V) Common Device Ground Input Clock (ƒCLK = 2 * ƒS) Output Enable (Low = Data) Channel A Tri-State Data Output (D0A = LSB) Channel B Tri-State Data Output (D0B = LSB) Channel A Overrange Bit Channel B Overrange Bit Data Valid Output MSB Invert (High = 2’s complement) (Low = binary) Reset (Low = Normal) (High = Reset) ORDERING INFORMATION PART NUMBER TEMPERATURE RANGE SPT7852SCT 0 to +70 °C SPT7852SIT –40 to +85 °C SPT7852SCU +25 °C *Please see the die specification for guaranteed electrical performance. PACKAGE TYPE 44L TQFP 44L TQFP Die* SPT7852 11 1/12/00