SPT7937 12-BIT, 28 MSPS, 170 mW A/D CONVERTER TECHNICAL DATA MARCH 5, 2002 FEATURES APPLICATIONS • Monolithic 28 MSPS analog-to-digital converter • 170 mW power dissipation • On-chip track-and-hold • Single +5 V power supply • TTL/CMOS outputs • 5 pF input capacitance • 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 • Digital communications DESCRIPTION The SPT7937 is a 12-bit monolithic, low-cost, low-power analog-to-digital converter capable of minimum sample rates of 28 MSPS. The SPT7937 has incorporated proprietary parallel SAR circuit design and CMOS processing technologies to achieve its advanced performance. The on-chip track-and-hold function assures very good dynamic performance without the need for external components. Power dissipation is extremely low at only 170 mW typical at 28 MSPS with a power supply of +5.0 V. The digital outputs are +3 V or +5 V, and are user selectable. Inputs and outputs are TTL/CMOS compatible to interface with TTL/ CMOS logic systems. Output data format is straight binary. The SPT7937 is available in a 28-lead SSOP package over the industrial temperature range. BLOCK DIAGRAM ADC Section 1 AIN 1:18 Mux AutoZero CMP T/H 13-Bit SAR D12 Out of Range 13 D11 (MSB) 13 P2 CLK In .. . D10 DAC P1 ADC Section 2 . . . Timing P17 and Control ADC Section 17 P18 ADC Section 18 . . . AutoZero CMP T/H D9 13-Bit SAR 13 DAC . . . 13 D8 13 13 13-Bit 18:1 Mux/ Error Correction D7 D6 D5 D4 D3 D2 D1 DØ (LSB) Reference Ladder VRHF VRHS VRLS VRLF ABSOLUTE MAXIMUM RATINGS (Beyond which damage may occur)1 25 °C Supply Voltages AVDD ...................................................................... +6 V DVDD ..................................................................... +6 V OVDD ..................................................................... +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 ................................. –0.7 V to VDD +0.7 V 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, VDD=+5.0 V, ƒS=28 MSPS, VIN=0 to 4 V, VRHS=4.0 V, VRLS=0.0 V, unless otherwise specified. PARAMETERS TEST CONDITIONS TEST LEVEL Resolution MIN SPT7937 TYP MAX 12 DC Accuracy Integral Linearity Error (ILE) Differential Linearity Error (DLE) No Missing Codes V V VI Analog Input Input Voltage Range Input Capacitance Input Bandwidth Input Impedance –Full-Scale Error1 +Full-Scale Error1 VI V V Conversion Characteristics Maximum Conversion Rate Minimum Conversion Rate Pipeline Delay (Latency) Aperture Delay Time (TAP) Aperture Jitter Time Clock Duty Cycle Over-Voltage Recovery Time2 Bits ±1.75 ±0.9 Guaranteed VRLS LSB LSB VRHS 5.0 250 35 1.0 0.12 V V VI V IV V V V 28 1 60 36 500 650 Ω 4.0 VDD 2.0 5.0 V V V 14 40 VI 350 IV IV V 3.0 0.0 1.0 Dynamic Performance Effective Number of Bits ƒIN = 3.58 MHz ƒIN = 10 MHz V VI V pF MHz kΩ LSB %FS MHz MHz Clock Cycles ns ps (RMS) % ns 1.0 5.0 Reference Input Resistance Voltage Range3 VRHS VRLS VRHS – VRLS UNITS 10.3 10.0 Bits Bits The full-scale range spans the reference ladder sense pins, VRHS and VRLS. Refer to the Voltage Reference section for discussion. Due to internal architecture, over-voltage recovery time is less than one clock cycle (i.e., 25 ns at ƒCLK = 40 MHz). 3 For optimum performance, the full-scale voltage range (VRHS–VRLS) should be between 3 V to 5 V. 1 2 SPT7937 2 3/5/02 ELECTRICAL SPECIFICATIONS TA=TMIN to TMAX, VDD=+5.0 V, ƒS=28 MSPS, VIN=0 to 4 V, VRHS=4.0 V, VRLS=0.0 V, unless otherwise specified. PARAMETERS TEST CONDITIONS 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 Spurious Free Dynamic Range ƒIN = 10 MHz Differential Phase Differential Gain MIN SPT7937 TYP V VI 61 65 63 V VI V VI –73 –72 60 V V V 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 CLK to Output Delay Time (tD) TEST LEVEL VI VI VI VI V IOH = 0.5 mA IOL = 1.6 mA Power Supply Requirements Voltages OVDD VDD Currents IDD Power Dissipation Power Supply Rejection Ratio 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. LEVEL I II III IV V VI MAX dB dB –63.5 dB dB 73 0.6 0.5 dB Degree % –10 –10 0.8 +10 +10 V V µA µA pF 0.4 V V ns 5 VDD – 0.5 IV IV VI VI V 3.0 4.75 dB dB 64 62 2.0 VI VI IV UNITS 15 5.0 34 170 60 5.0 5.25 40 200 V V mA mW dB 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. SPT7937 3 3/5/02 Figure 1a – Timing Diagram 1 10 2 11 12 13 9 3 ANALOG IN 8 4 5 6 17 14 7 15 16 CLOCK IN INVALID VALID DATA OUTPUT 1 2 3 Figure 1b – Timing Diagram tCLK tC tCH tCL CLOCK IN DATA OUTPUT Data Ø Data 1 Data 2 Data 3 tD SPT7937 4 3/5/02 TYPICAL PERFORMANCE CHARACTERISTICS THD, SNR, SINAD vs Input Frequency THD, SNR, SINAD vs Sample Rate 75 90 80 THD, SNR, SINAD (dB) THD, SNR, SINAD (dB) 70 THD 65 SNR 60 SINAD 55 THD 70 SNR 60 SINAD 50 50 40 45 0 5 10 15 30 20 0 Input Frequency (MHz) 1 5 85 80 80 75 75 THD 70 65 30 40 50 70 65 SNR 60 60 SINAD 55 55 40 0 25 70 85 55 125 55 Temperature (°C) 5 25 10 20 IDD (mA) 30 15 10 25 5 300 400 25 70 85 125 15 20 200 0 IDD vs Sample Rate 0 30 100 40 Temperature (°C) Input Bandwidth Output Fundamental (dBm) 20 SFDR vs Temperature 85 SFDR (dB) THD, SNR, SINAD (dB) THD, SNR, SINAD vs Temperature 10 Sample Rate (MSPS) 500 0 1000 Frequency (MHz) 101 100 101 102 Sample Rate (MSPS) SPT7937 5 3/5/02 Figure 2 – Typical Interface Circuit CLK IN Out of Range Bit + DGND D11 CLK D10 DVDD D9 AVDD D8 U1 DGND (DUT) VINR AIN VIN +A5 U1 TK11240B + Ext VREF (+4 V) D7 D6 D5 RGND D4 VRHS D3 VRHF D2 VRLF D1 VRLS D0 DVDD2 OVDD LSB 1 + 28 MSB Interfacing Logic +A5 D12 SPT7937 + OGND FB +D3/5V +A5 +D3/5V +D3/5 + + 10 F 10 F +A5 AGND +D3/5 DGND Notes: 1) Unless otherwise specified, all non-polarized capacitors are 0.01 microfarad surface-mount chip capacitors. They need to be placed as close to the pin as possible 2) All polarized capacitors are 4.7 to 10 microfarad tantalum surface-mount capacitors 3) FB is a ferrite bead. Place FB as close to the DUT as possible 4) U1 is TOKO regulator TK11240B (4.0 V) TYPICAL INTERFACE CIRCUIT POWER SUPPLIES AND GROUNDING Very few external components are required to achieve the stated device performance. Figure 2 shows the typical interface requirements when using the SPT7937 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 (DVDD ) and the analog (AVDD) supply voltages on the SPT7937 be derived from a single analog supply as shown in figure 2. A separate digital supply should be used for the digital output driver supply (OVDD) and all interface circuitry. CADEKA suggests using this power supply configuration to prevent a possible latch-up condition on power up. In addition, the power supplies must be powered up before the analog input is applied. SPT7937 6 3/5/02 OPERATING DESCRIPTION VOLTAGE REFERENCE The general architecture for the CMOS ADC is shown in the block diagram. The design contains 18 identical successive approximation ADC sections (all operating in parallel), an 18-phase clock generator, a 13-bit 18:1 digital output multiplexer, correction logic, and a voltage reference generator which provides common reference levels for each ADC section. The SPT7937 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 full-scale range will track the total voltage difference measured between the ladder sense lines, VRHS and VRLS. For optimum performance the full-scale voltage range (VRHS– VRLS) should be between 3 V to 5 V. 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 18 clock cycles to complete a conversion. The clock cycles are allocated as follows: 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. Table II – Clock Cycles Clock Operation 1 Reference zero sampling 2 Auto-zero comparison 3 Auto-calibrate comparison 4 Input sample 5-17 13-bit SAR conversion 18 Data transfer Figure 3 – Ladder Force/Sense Circuit + The 18-phase clock, which is derived from the input clock, synchronizes these events. The timing signals for adjacent ADC sections are shifted by one clock cycle so that the analog input is sampled on every cycle of the input clock by exactly one ADC section. After 18 clock periods, the timing cycle repeats. The latency from analog input sample to the corresponding digital output is 14 clock cycles. 1 AGND 2 VRHF 3 VRHS 4 N/C 5 + • Since only 18 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 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. VRLS 6 VRLF 7 VIN All capacitors are 0.01 µF SPT7937 7 3/5/02 ANALOG INPUT Figure 4 – Simplified Reference Ladder Drive Circuit Without Force/Sense Circuit +4.0 V External Reference 21 mV VRHS (+3.91 V) 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 the Voltage Reference section.) R/2 The drive requirements for the analog inputs are very minimal when compared to most other converters due to the SPT7937’s extremely low input capacitance of only 5 pF and very high input resistance in excess of 35 kΩ. R R R The analog input should be protected through a series resistor and diode clamping circuit as shown in figure 5. To prevent possible latch-up condition, the power supplies must be powered up before the input is applied. R=30 W (typ) All capacitors are 0.01 µF R R Figure 5 – Recommended Input Protection Circuit R VRLS (0.075 V) 50 mV +V AVDD R/2 VRLF (AGND) 0.0 V D1 Buffer In cases in which 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 force and sense lines to AGND with a 0.01 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: ADC 47 W D2 V D1 = D2 = Hewlett Packard HP5712 or equivalent 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. CALIBRATION The SPT7937 uses a user-transparent, auto-calibration scheme to ensure 12-bit accuracy over time and temperature. Gain and offset errors are continually adjusted to 12-bit accuracy during device operation. Typically, the top side voltage drop for VRHF to VRHS will equal: Upon powerup, the SPT7937 begins its calibration algorithm. In order to achieve the calibration accuracy required, the offset and gain adjustment step size is a fraction of a 12-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 357 µsec (for a 28 MHz clock). Once calibrated, the SPT7937 remains calibrated over time and temperature. VRHF – VRHS = 0.5% of (VRHF – VRLF) (typical), and the bottom side voltage drop for VRLS to VRLF will equal: VRLS – VRLF = 1.25% 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 21 mV drop is seen at VRHS (= 3.79 V) and a 50 mV increase is seen at VRLS (= 0.050 V). Since the calibration cycles are initiated on the rising edge of the clock, the clock must be continuously applied for the SPT7937 to remain in calibration. SPT7937 8 3/5/02 DIGITAL OUTPUTS Figure 6 – On-Chip Protection Circuit VDD 120 W The digital outputs (D0–D12) are driven by a separate supply (OVDD) ranging from +3 V to +5 V. This feature makes it possible to drive the SPT7937’s TTL/CMOS-compatible outputs with the user’s logic system supply. The format of the output data (D0–D11) is straight binary. (See table III.) The outputs are latched on the rising edge of CLK. Analog 120 W Pad Table III – Output Data Information ANALOG INPUT INPUT PROTECTION OUT OF RANGE D12 OUTPUT CODE D11–D0 +F.S. + 1/2 LSB 1 1111 1111 1111 +F.S. –1/2 LSB 0 1111 1111 111Ø +1/2 F.S. 0 ØØØØ ØØØØ ØØØØ +1/2 LSB 0 0000 0000 000Ø 0.0 V 1 0000 0000 0000 (Ø indicates the flickering bit between logic 0 and 1). 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. OUT-OF-RANGE OUTPUT The Out-of-Range Output (D12) is an indication that the analog input signal is outside the full-scale input voltage range by 1 LSB. When this condition occurs, D12 will switch to logic 1. All other data outputs (D0 to D11) will remain at logic 0 or 1 as long as D12 remains at logic 1. CLOCK INPUT The SPT7937 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. EVALUATION BOARD The EB7937 evaluation board is available to aid designers in demonstrating the full performance of the SPT7937. This board includes a reference circuit, clock driver circuit, output data latches and an on-board reconstruction of the digital data. An application note (AN7937) describing the operation of this board, as well as information on the testing of the SPT7937, is also available. Contact the factory for price and availability. SPT7937 9 3/5/02 PACKAGE OUTLINE 28-Lead SSOP INCHES 28 I H MIN MAX MIN MAX A 0.397 0.407 10.07 10.33 B 0.002 0.008 0.05 0.21 C D 1 A MILLIMETERS SYMBOL 0.0256 typ 0.010 0.015 0.65 typ 0.25 0.38 E 0.004 0.008 0.09 0.20 F 0.066 0.070 1.68 1.78 G 0.025 0.037 0.63 0.95 H 0.301 0.311 7.65 7.90 I 0.205 0.212 5.20 5.38 F B C D H G E SPT7937 10 3/5/02 PIN ASSIGNMENTS OVDD 1 PIN FUNCTIONS 28 DVDD2 D0 (LSB) 2 27 VRLS D1 3 26 VRLF D2 4 25 VRHF Name Function OVDD Digital Output Driver Supply D0–D11 Data Output, Bits 0 – Bit 11 D12 Out of Range OGND Digital Output Driver Ground DGND Digital Ground CLK Input Clock D3 5 24 VRHS Digital VDD 6 23 DVDD1 D4 RGND DVDD2 Digital VDD; must be tied to DVDD1 22 VIN AVDD Analog VDD 21 VINR 20 19 D5 7 D6 8 D7 9 D8 28L SSOP 10 AGND Analog Ground VINR Analog Input Return AGND VIN Analog Input, Full Scale from VRLS to VRHS AVDD RGND Analog Ground Shield (Junction Isolated) VRHS Reference High Sense VRHF Reference High Force (VRHF≤AVDD) VRLS Reference Low Sense VRLF Reference Low Force DVDD1 D9 11 18 D10 12 17 CLK D11 (MSB) 13 16 DGND D12 14 15 OGND ORDERING INFORMATION PART NUMBER SPT7937SIR TEMPERATURE RANGE PACKAGE –40 to +85 °C 28L SSOP SPT7937 11 3/5/02