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| SPT7852 DUAL 10-BIT, 20 MSPS, 160 mW A/D CONVERTER FEATURES * * * * * * 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 APPLICATIONS * * * * * * 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 ADCA Output Buffer Overrange DA0-9 Reference In Reference Ladder VINB T/H ADCB 10 Output Buffer Overrange DB0-9 Clock Reset Output Enable Timing Generation ABSOLUTE MAXIMUM RATINGS (Beyond which damage may occur)1 25 C Supply Voltages AVDD ......................................................................... +6 V DVDD ......................................................................... +6 V 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: 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 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, S =20 MSPS, CLK =40 MHz, VRHS =4.0 V, VRLS =0.0 V, unless otherwise specified. PARAMETERS Resolution DC Accuracy Integral Nonlinearity Differential Nonlinearity Analog Input Input Voltage Range Input Resistance Input Capacitance Input Bandwidth Offset Gain Error Reference Input Resistance Voltage Range VRLS VRHS VRHS - VRLS (VRHF - VRHS) (VRLS - VRLF) Conversion Characteristics Maximum Conversion Rate1 Minimum Conversion Rate1 Pipeline Delay (Latency) Aperture Delay Time Aperture Jitter Time Dynamic Performance Effective Number of Bits IN=3.58 MHz IN= 10 MHz 12X TEST CONDITIONS TEST LEVEL MIN 10 TYP MAX UNITS Bits IV IV V V V V VI VI VI IV IV V V V VI IV IV V V VRLS 50 1.0 1.0 VRHS 5.0 35 2.0 2.0 350 0 3.0 1.0 425 4.0 150 150 500 2.0 AVDD 5.0 LSB LSB V k pF MHz LSB LSB V V V mV mV MHz kHz Clock Cycles ns ps Full Power VRHS - VRLS 20 100 12 5 15 VI VI 8.4 7.9 8.9 8.4 Bits Bits Clock required. SPT7852 2 1/12/00 ELECTRICAL SPECIFICATIONS TA=TMIN to TMAX, AVDD = DVDD = +5.0 V, VIN =0 to 4 V, S =20 MSPS, CLK =40 MHz, VRHS = 4.0 V, VRLS =0.0 V, unless otherwise specified. PARAMETERS TEST CONDITIONS TEST LEVEL MIN TYP MAX UNITS Dynamic Performance Signal-to-Noise Ratio (without Harmonics) IN=3.58 MHz IN=10 MHz Harmonic Distortion IN=3.58 MHz IN=10 MHz Signal-to-Noise and Distortion (SINAD) IN=3.58 MHz IN=10 MHz Channel-to-Channel Crosstalk IN=3.58 MHz Channel-to-Channel Gain Matching Full Scale Spurious Free Dynamic Range IN=3.58 MHz @ -3 dB FS Differential Phase Differential Gain Digital Inputs Logic "1" Voltage Logic "0" Voltage Maximum Input Current Low Maximum Input Current High Input Capacitance 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 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. VI VI VI VI 53 52 56 52 57 56 59 54 dB dB dB dB VI VI IV IV V V V VI VI VI VI V VI VI V V V IV IV IV VI VI VI 52 49 55 52 70 0.04 66 0.2 0.3 dB dB dB dB dB Degree % V V A A pF V V ns ns ns V V V mA mA mW 2.0 -10 -10 5 OVDD-0.5 0.4 10 10 22 4.75 4.75 2.7 5.0 5.0 5.0 15 17 160 5.25 5.25 5.25 18 20 190 0.8 +10 +10 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 I II III IV V VI TEST PROCEDURE 100% production tested at the specified temperature. 100% production tested at TA=+25 C, and sample tested at the specified temperatures. QA sample tested only at the specified temperatures. Parameter is guaranteed (but not tested) by design and characterization data. Parameter is a typical value for information purposes only. 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 3-st EN Ref In (+4 V) MSBINV VRHF VRHS VRLS VRLF VCAL Reset EN Digital Output A 11 SPT7852 DAV Interfacing Logic 11 VIN1 VIN2 Clock VINA VINB CLK AVDD DVDD .1 F GND Digital Output B OVDD .1 F FB * 4.7 F +A5 1. 2. 3. 4. 4.7 F FB * 3.3 V/5 V Place the ferrite bead (*) as close to the ADC as possible. Place 0.1 F decoupling capacitors as close to the ADC as possible. All capacitors are 0.1 F surface-mount unless otherwise specified. All analog input pins (references, analog input, clock input) must be protected. (See absolute maximum ratings.) TYPICAL INTERFACE CIRCUIT 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. POWER SUPPLIES AND GROUNDING 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 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: Table I - Clock Cycles Clock 1 2 3 4 5-15 16 Operation Reference zero sampling Auto-zero comparison Auto-calibrate comparison Input sample 11-bit SAR conversion Data transfer 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. * 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. * 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 1 td 3 tSet Data Valid (DAV) Data Output (Channel A) Data Output (Channel B) tOD tHold Invalid 4 Invalid Invalid tOD Invalid Invalid 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. 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 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. 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 5 2 3 4 6 7 8 9 10 11 Analog In (Channel A) Analog In (Channel B) Clock In Reset Sampling Clock (Internal) Data Out (Channel A) Invalid 1 Valid 2 3 4 Invalid Data Out (Channel B) Data Valid 1 Valid 2 3 4 Table II - Timing Parameters Table DESCRIPTION PARAMETERS tc tCLK MIN 2*tCLK 25 40 TYP MAX UNITS ns ns % ns ns ns 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 50 11 tCLK 15 60 tOD tDAV td tSet tHold 22 28 SPT7852 7 1/12/00 Figure 4 - Ladder Force/Sense Circuit Figure 5 - Simplified Reference Ladder Drive Circuit Without Force/Sense Circuit +4.0 V External Reference VRHS (+3.85 V) + - 1 VRHF 150 mV R/2 2 VRHS R R 3 VRLS R R=30 (typ) All capacitors are 0.01 F R 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. 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. 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 F capacitor (chip cap preferred) to minimize high-frequency noise injection. If this simplified configuration is used, the following considerations should be taken into account: 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: VRHF - VRHS = 3.75% of (VRHF - VRLF) (typical), and the bottom side voltage drop for VRLS to VRLF will equal: VRLS - VRLF = 3.75% of (VRHF - VRLF) (typical). 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 + - 4 VRLF AGND VRLS (0.150 V) VRLF (AGND) 0.0 V 150 mV R R 5 R/2 All capacitors are 0.01 F 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). 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.) 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 k. The analog input should be protected through a series resistor and diode clamping circuit as shown in figure 6. Figure 6 - Recommended Input Protection Circuit +V AVDD D1 Buffer 47 D2 ADC -V D1 = D2 = Hewlett Packard HP5712 or equivalent SPT7852 8 1/12/00 CALIBRATION 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. 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 sec (for a 20 MHz sample rate). Once calibrated, the SPT7852 remains calibrated over time and temperature. 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. POWER SUPPLY SEQUENCING CONSIDERATIONS 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. 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. 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. Table III - Output Data Information (Binary Code) 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 VDD 120 Analog 120 Pad 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 O 01 1 1 1 1 1 1 1 O [+FS -(-FS)]/2 0 OO OOOO OOOO OO OOOO OOOO -FS + 1/2 LSB 0 00 0000 000O 10 0000 000O -FS 0 00 0000 0000 10 0000 0000 O indicates the flickering bit between logic 0 and 1. +FS = VRHS; -FS = VRLS SPT7852 9 1/12/00 PACKAGE OUTLINE 44-LEAD TQFP A B INCHES SYMBOL A B MIN 0.472 Typ 0.394 Typ 0.394 Typ 0.472 Typ 0.031 Typ 0.012 0.035 0.002 0.018 0.039 Typ 0-7 0.017 0.040 0.006 0.030 MAX MILLIMETERS MIN 12.00 Typ 10.00 Typ 10.00 Typ 12.00 Typ 0.80 Typ 0.300 0.85 0.05 0.450 1.00 Typ 0-7 0.45 1.05 0.15 0.750 MAX Pin 1 Index C D E F C D G H I J K E F G I H J K SPT7852 10 1/12/00 PIN ASSIGNMENTS OVDD AVDD 44 1 2 3 4 5 6 7 8 9 10 11 PIN FUNCTIONS NAME VRHF VRHS VRLS VRLF VCAL VINA VINB AVDD DVDD OVDD GND CLK 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 (CLK = 2 * S) 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) D10A D8A D7A D5A D6A D9A EN DVDD 43 GND 42 40 37 34 39 36 41 38 35 VRHF VRHS VRLS VRLF GND VINA GND VINB MSBINV Reset VCAL 33 32 31 30 29 D4A D3A D2A D1A D0A DAV D0B D1B D2B D3B D4B TOP VIEW 28 27 26 25 24 23 EN D0A - D9A D0B - D9B 16 19 22 14 17 20 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* 12 15 18 21 13 OVDD AVDD DVDD D10B D9B GND CLK D8B D5B D6B D7B D10A D10B DAV MSBINV Reset SPT7852 11 1/12/00 |
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