SPT7835 10-BIT, 5 MSPS, 75 mW A/D CONVERTER TECHNICAL DATA JUNE 27, 2001 FEATURES APPLICATIONS • Monolithic 5 MSPS converter • 75 mW power dissipation • On-chip track-and-hold • Single +5 V power supply • TTL/CMOS outputs • 5 pF input capacitance • Low cost • Tri-state output buffers • High ESD protection: 3,500 V minimum • Selectable +3 V or +5 V logic I/O • All high-speed applications where low power dissipation is required • Video imaging • Medical imaging • IR imaging • Scanners • Digital communications GENERAL DESCRIPTION SPT7835 is pin-compatible with an entire family of 10-bit, CMOS converters (SPT7835/40/50/55/60/61), which simplifies upgrades. The SPT7835 has incorporated proprietary circuit design* and CMOS processing technologies to achieve its advanced performance. Inputs and outputs are TTL/CMOS-compatible to interface with TTL/CMOS logic systems. Output data format is straight binary. The SPT7835 is a 10-bit monolithic, low-cost, ultralowpower analog-to-digital converter capable of minimum word rates of 5 MSPS. The on-chip track-and-hold function assures very good dynamic performance without the need for external components. The input drive requirements are minimized due to the SPT7835’s low input capacitance of only 5 pF. Power dissipation is extremely low at only 75 mW typical at 5 MSPS with a power supply of +5.0 V. The digital outputs are +3 V or +5 V, and are user selectable. The The SPT7835 is available in a 28-lead SOIC package over the industrial temperature range, and a 32-lead small (7 mm square) TQFP package over the commercial temperature range. *Patent pending BLOCK DIAGRAM ADC Section 1 AIN 1:8 Mux T/H AutoZero CMP 11-Bit SAR D10 Overrange 11 D9 (MSB) 11 CLK In .. . P2 Timing P7 and Control Enable P8 .. . ADC Section 7 .. . 11 .. . ADC Section 2 ADC Section 8 T/H Data Valid D8 DAC P1 AutoZero CMP 11 11-Bit SAR D7 11 11-Bit 8:1 Mux/ Error Correction D6 D5 D4 D3 11 D2 DAC D1 Ref In Reference Ladder D0 (LSB) VREF 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 ............................ –40 to 85 °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 .............................................................. 0 to AVDD CLK Input ............................................................... VDD AVDD – DVDD .................................................. ±100 mV AGND – DGND .............................................. ±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 TA=TMIN to TMAX, AVDD=DVDD=OVDD=+5.0 V, VIN=0 to 4 V, ƒCLK=10 MHz, ƒS=5 MSPS, VRHS=4.0 V, VRLS=0.0 V, unless otherwise specified. PARAMETERS TEST CONDITIONS TEST LEVEL Resolution MIN SPT7835 TYP MAX 10 DC Accuracy Integral Linearity Error (ILE) Differential Linearity Error (DLE) No Missing Codes VI VI VI Analog Input Input Voltage Range Input Resistance Input Capacitance Input Bandwidth Offset Gain Error VI IV V V V V VRLS 50 (Small Signal) 400 100 IV IV V V V 0 3.0 1.0 Reference Settling Time VRHS VRLS V V Conversion Characteristics Maximum Conversion Rate Minimum Conversion Rate Pipeline Delay (Latency) Aperture Delay Time Aperture Jitter Time VI IV IV V V VRHS V kΩ pF MHz LSB LSB 500 150 600 Ω MHz 4.0 90 75 2.0 AVDD 5.0 Clock Cycles Clock Cycles 5 10 MHz MHz Clock Cycles ns ps (p-p) 9.2 Bits 59 dB 12 54 V V V mV mV 15 20 5 2 VI VI LSB LSB 5.0 100 ±2.0 ±2.0 VI V Dynamic Performance Effective Number of Bits (ENOB) ƒIN = 1 MHz Signal-to-Noise Ratio (SNR) (without Harmonics) ƒIN = 1 MHz Bits ±1.0 ±0.5 Guaranteed Reference Input Resistance Bandwidth Voltage Range VRLS VRHS VRHS – VRLS ∆(VRHF – VRHS) ∆(VRLS – VRLF) UNITS SPT7835 2 6/27/01 ELECTRICAL SPECIFICATIONS TA=TMIN to TMAX, AVDD=DVDD=OVDD=+5.0 V, VIN=0 to 4 V, ƒCLK=10 MHz, ƒS=5 MSPS, VRHS=4.0 V, VRLS=0.0 V, unless otherwise specified. PARAMETERS TEST CONDITIONS TEST LEVEL Dynamic Performance Total Harmonic Distortion (THD) ƒIN = 1 MHz Signal-to-Noise and Distortion (SINAD) ƒIN = 1 MHz Spurious Free Dynamic Range 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 OVDD DVDD AVDD Currents AIDD DIDD Power Dissipation MIN 63 dB VI V 52 57 63 dB dB VI VI VI VI V 2.0 5 3.0 4.75 4.75 ƒIN = 1 MHz IV IV IV VI VI VI 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. I II III IV V VI 0.8 +10 +10 –10 –10 3.5 All electrical characteristics are subject to the following conditions: UNITS 59 VI VI V V V V LEVEL MAX VI IOH = 0.5 mA IOL = 1.6 mA 15 pF load 15 pF load 20 pF load, TA = +25 °C 50 pF load over temp. TEST LEVEL CODES SPT7835 TYP 0.4 10 10 10 22 5.0 5.0 9 6 75 5.0 5.25 5.25 12 10 110 V V µA µA pF V V ns ns ns ns V V V mA mA mW 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. SPT7835 3 6/27/01 SPECIFICATION DEFINITIONS APERTURE DELAY INTEGRAL LINEARITY ERROR (ILE) Aperture delay represents the point in time, relative to the rising edge of the CLOCK input, that the analog input is sampled. Linearity error refers to the deviation of each individual code (normalized) from a straight line drawn from –FS through +FS. The deviation is measured from the edge of each particular code to the true straight line. APERTURE JITTER OUTPUT DELAY The variations in aperture delay for successive samples. Time between the clock’s triggering edge and output data valid. DIFFERENTIAL GAIN (DG) A signal consisting of a sine wave superimposed on various DC levels is applied to the input. Differential gain is the maximum variation in the sampled sine wave amplitudes at these DC levels. OVERVOLTAGE RECOVERY TIME The time required for the ADC to recover to full accuracy after an analog input signal 125% of full scale is reduced to 50% of the full-scale value. DIFFERENTIAL PHASE (DP) SIGNAL-TO-NOISE RATIO (SNR) A signal consisting of a sine wave superimposed on various DC levels is applied to the input. Differential phase is the maximum variation in the sampled sine wave phases at these DC levels. The ratio of the fundamental sinusoid power to the total noise power. Harmonics are excluded. SIGNAL-TO-NOISE AND DISTORTION (SINAD) EFFECTIVE NUMBER OF BITS (ENOB) The ratio of the fundamental sinusoid power to the total noise and distortion power. SINAD = 6.02N + 1.76, where N is equal to the effective number of bits. SINAD – 1.76 N= 6.02 TOTAL HARMONIC DISTORTION (THD) The ratio of the total power of the first 9 harmonics to the power of the measured sinusoidal signal. INPUT BANDWIDTH Small signal (50 mV) bandwidth (3 dB) of analog input stage. SPURIOUS FREE DYNAMIC RANGE (SFDR) The ratio of the fundamental sinusoidal amplitude to the single largest harmonic or spurious signal. DIFFERENTIAL LINEARITY ERROR (DLE) Error in the width of each code from its theoretical value. (Theoretical = VFS/2N) SPT7835 4 6/27/01 Figure 1A – Timing Diagram 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 ANALOG IN CLOCK IN SAMPLING CLOCK (Internal) INVALID VALID 1 DIGITAL OUT 2 3 4 5 6 7 8 9 10 11 DATA VALID Figure 1B – Timing Diagram 2 tC tCH tCL tCLK CLOCK IN tOD DATA OUTPUT Data 1 Data 0 Data 2 tDAV DATA VALID tDAV tS Table I – Timing Parameters DESCRIPTION PARAMETERS MIN tC 2*tCLK ns Clock Period tCLK 100 ns Clock High Duty Cycle tCH 40 50 60 % Clock Low Duty Cycle tCL 40 50 60 % Clock to Output Delay (15 pF Load) tOD 15 20 25 ns DAV Pulse Width tDAV Conversion Time Clock to DAV TYP MAX tCLK tS 16 21 UNITS ns 26 ns SPT7835 5 6/27/01 TYPICAL PERFORMANCE CHARACTERISTICS SNR vs Input Frequency THD vs Input Frequency 80 Total Harmonic Distortion (dB) Signal-to-Noise Ratio (dB) 80 70 S = 5 MSPS 60 50 40 30 20 101 Input Frequency (MHz) 70 60 50 40 30 20 101 100 80 100 110 70 Power Dissipation (mW) Signal-to-Noise and Distortion (dB) Input Frequency (MHz) Total Power Dissipation vs Sample Rate Reference is excluded = 30 mW Typ SINAD vs Input Frequency S = 5 MSPS 60 50 40 30 20 101 S = 5 MSPS 90 70 50 30 Input Frequency (MHz) 100 10 0 Sample Rate (CLK/2) MHz 5 SPT7835 6 6/27/01 Figure 2 – Typical Interface Circuit Ref In (+4 V) VRHF VRHS VRLS VRLF VIN VIN SPT7835 VCAL CLK IN 3.3/5 OGND D4 Interfacing Logics D3 D2 D1 D0 CLK DAV AVDD D10 D9 D8 D7 D6 D5 OVDD AGND EN DGND* DVDD 3.3/5 Enable/Tri-State (Enable = Active Low) +A5 L1 AGND +A5 + 10 µF +5 V Analog +5 V Analog RTN DGND *To reduce the possibility of latch-up, avoid connecting the DGND pins of the ADC to the digital ground of the system. 3.3/5 + 10 µF +5 V Digital RTN +5 V Digital NOTES: 1) L1 is to be located as closely to the device as possible. 2) All capacitors are 0.1 µF surface-mount unless otherwise specified. 3) L1 is a 10 µH inductor or a ferrite bead. TYPICAL INTERFACE CIRCUIT OPERATING DESCRIPTION Very few external components are required to achieve the stated device performance. Figure 2 shows the typical interface requirements when using the SPT7835 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. The general architecture for the CMOS ADC is shown in the block diagram. The design contains 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 that 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 CADEKA suggests that both the digital and the analog sup- signal in sequence. Each ADC uses 16 clock cycles to ply voltages on the SPT7835 be derived from a single ana- complete a conversion. The clock cycles are allocated as log supply as shown in figure 2. A separate digital supply shown in table II. should be used for all interface circuitry. CADEKA suggests using this power supply configuration to prevent a possible latch-up condition on powerup. POWER SUPPLIES AND GROUNDING SPT7835 7 6/27/01 Table II – Clock Cycles Clock 1 2 3 4 5-15 16 Figure 3 – Ladder Force/Sense Circuit Operation Reference zero sampling Auto-zero comparison Auto-calibrate comparison Input sample 11-bit SAR conversion Data transfer AGND + VRHF VRHS 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 10 MHz clock rate, the input sample rate is 5 MHz. The latency from analog input sample to the corresponding digital output is 12 clock cycles. VRLS + VRLF VIN All capacitors are 0.01 µF • Since only eight 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 comparators’ 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 samples the input during a clock cycle. • The total input capacitance is very low since sections of the converter that are not sampling the signal are isolated from the input by transmission gates. Figure 4 – Reference Ladder +4.0 V External Reference 90 mV VRHS (+3.91 V) R/2 R R R R=30 W (typ) All capacitors are 0.01 µF R R VOLTAGE REFERENCE R The SPT7835 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. 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. VRLS (0.075 V) VRLF (AGND) 0.0 V 75 mV R/2 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. 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 3, offset and gain errors of less than ±2 LSB can be obtained. The reference ladder circuit shown in figure 4 is a simplified representation of the actual reference ladder with force and sense taps shown. Due to the actual internal structure of the ladder, the voltage drop from VRHF to VRHS is not equivalent to the voltage drop from VRLF to VRLS. 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 4. Decouple SPT7835 8 6/27/01 Typically, the top side voltage drop for VRHF to VRHS will equal: Upon powerup, the SPT7835 begins its calibration algorithm. In order to achieve the calibration accuracy required, the offset and gain adjustment step size is a fraction of a 10-bit LSB. Since the calibration algorithm is an oversampling process, a minimum of 10,000 clock cycles are required. This results in a minimum calibration time upon powerup of 1 msec for a 5 MHz sample rate. Once calibrated, the SPT7835 remains calibrated over time and temperature. VRHF – VRHS = 2.25 % of (VRHF – VRLF) (typical), and the bottom side voltage drop for VRLS to VRLF will equal: VRLS – VRLF = 1.9 % of (VRHF – VRLF) (typical). Figure 4 shows an example of expected voltage drops for a specific case. VREF of 4.0 V is applied to VRHF, and VRLF is tied to AGND. A 90 mV drop is seen at VRHS (= 3.91 V), and a 75 mV increase is seen at VRLS (= 0.075 V). Since the calibration cycles are initiated on the rising edge of the clock, the clock must be continuously applied for the SPT7835 to remain in calibration. ANALOG INPUT INPUT PROTECTION VIN is the analog input. 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.) All I/O pads are protected with an on-chip protection circuit shown in figure 6. This circuit provides ESD robustness to 3.5 kV and prevents latch-up under severe discharge conditions without degrading analog transition times. The drive requirements for the analog inputs are very minimal when compared to most other converters due to the SPT7835’s extremely low input capacitance of only 5 pF and very high input resistance of 50 kΩ. Figure 6 – On-Chip Protection Circuit VDD The analog input should be protected through a series resistor and diode clamping circuit as shown in figure 5. 120 W Figure 5 – Recommended Input Protection Circuit +V Analog 120 W AVDD Pad D1 Buffer ADC 47 W D2 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 that could delay VDD power to the device. V D1 = D2 = Hewlett-Packard HP5712 or equivalent CALIBRATION CLOCK INPUT The SPT7835 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. The SPT7835 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 figure 1A timing diagram.) SPT7835 9 6/27/01 DIGITAL OUTPUTS OVERRANGE OUTPUT The digital outputs (D0–D10) are driven by a separate supply (OVDD) ranging from +3 V to +5 V. This feature makes it possible to drive the SPT7835’s TTL/CMOScompatible outputs with the user’s logic system supply. The format of the output data (D0–D9) is straight binary. (See table III.) The outputs are latched on the rising edge of CLK. These outputs can be switched into a tri-state mode by bringing EN high. The OVERRANGE OUTPUT (D10) is an indication that the analog input signal has exceeded the positive fullscale input voltage by 1 LSB. When this condition occurs, D10 will switch to logic 1. All other data outputs (D0 to D9) will remain at logic 1 as long as D10 remains at logic 1. This feature makes it possible to include the SPT7835 in higher resolution systems. EVALUATION BOARD Table III – Output Data Information The EB7835 evaluation board is available to aid designers in demonstrating the full performance of the SPT7835. This board includes a reference circuit, clock driver circuit, output data latches, and an on-board reconstruction of the digital data. An application note describing the operation of this board, as well as information on the testing of the SPT7835, is also available. Contact the factory for price and availability. ANALOG INPUT OVERRANGE OUTPUT CODE D10 D9–D0 +F.S. + 1/2 LSB 1 11 1111 1111 +F.S. –1/2 LSB 0 1 1 1 1 1 1 1 1 1Ø +1/2 F.S. 0 ØØ ØØØØ ØØØØ +1/2 LSB 0 00 0000 000Ø 0.0 V 0 00 0000 0000 (Ø indicates the flickering bit between logic 0 and 1.) SPT7835 10 6/27/01 PACKAGE OUTLINES 28-Lead SOIC 28 SYMBOL A B C D E F G H I I H 1 INCHES MIN MAX 0.699 0.709 0.005 0.011 0.050 typ 0.018 typ 0.0077 0.0083 0.090 0.096 0.031 0.039 0.396 0.416 0.286 0.292 MILLIMETERS MIN MAX 17.75 18.01 0.13 0.28 1.27 typ 0.46 typ 0.20 0.21 2.29 2.44 0.79 0.99 10.06 10.57 7.26 7.42 INCHES MIN MAX 0.346 0.362 0.272 0.280 0.346 0.362 0.272 0.280 0.031 typ 0.012 0.016 0.053 0.057 0.002 0.006 0.037 0.041 0.007 0° 7° 0.020 0.030 MILLIMETERS MIN MAX 8.80 9.20 6.90 7.10 8.80 9.20 6.90 7.10 0.80 BSC 0.30 0.40 1.35 1.45 0.05 0.15 0.95 1.05 0.17 0° 7° 0.50 0.75 A F B C D H G E 32-Lead TQFP G H A SYMBOL A B C D E F G H I J K L B C D I J E F K L SPT7835 11 6/27/01 PIN ASSIGNMENTS PIN FUNCTIONS AGND 1 28 VRHF 2 27 D9 VRHS 3 26 D8 D10 Name Function AGND Analog Ground VRHF Reference High Force VRHS Reference High Sense D7 VRLS Reference Low Sense VRLS 5 24 D6 VRLF Reference Low Force VRLF 6 23 D5 VCAL Calibration Reference VIN 7 22 VIN Analog Input AVDD Analog VDD DVDD Digital VDD DGND Digital Ground CLK Input Clock ƒCLK = FS (TTL) N/C AGND VCAL 25 4 SOIC 21 8 OVDD OGND 20 D4 9 AVDD 10 19 D3 DVDD 11 18 D2 DGND 12 17 D1 EN Output Enable D0–9 Tri-State Data Output, (D0=LSB) DAV Data Valid Output OVDD Digital Output Supply OGND Digital Output Ground N/C No Connect D8 EN D9 15 D10 DAV 14 AGND Tri-State Output Overrange VRHF D10 AGND D0 VRLS 16 VRHS CLK 13 25 27 26 28 30 29 31 32 VRLF 1 24 D7 VIN 2 23 D6 AGND 3 22 D5 AGND 4 21 OVDD VCAL 5 20 OGND AVDD 6 19 D4 AVDD 7 18 D3 DVDD 8 17 D2 TQFP D1 EN 16 14 CLK DAV 15 D0 13 11 DGND DVDD DGND 12 9 10 ORDERING INFORMATION PART NUMBER TEMPERATURE RANGE PACKAGE TYPE SPT7835SIS –40 to +85 °C 28L SOIC SPT7835SCT 0 to +70 °C 32L TQFP SPT7835 12 6/27/01