SPT7820

SPT7820 10-BIT, 20 MSPS, TTL OUTPUT, A/D CONVERTER FEATURES • • • • • • • Monolithic 20 MSPS Converter On-Chip Track/Hold Bipolar ±2.0 V Analog Input 60 dB SNR @ 1 MHz Input Low Power (1.0 W Typical) 5 pF Input Capacitance TTL Outputs APPLICATIONS • • • • • • Medical Imaging Professional Video Radar Receivers Instrumentation Electronic Warfare Digital Communications GENERAL DESCRIPTION The SPT7820 A/D converter is a 10-bit monolithic converter capable of word rates of a min imum of 20 MSPS. On board track/hold function assures excellent dynamic performance without the need for external components. Drive requirement problems are minimized with an input capacitance of only 5 pF. Inputs and outputs are TTL compatible to interface with TTL logic systems. An overrange output signal is provided to indicate overflow conditions. Output data format is straight binary. Power dissipation is very low at only 1.0 watt with power supply voltages of +5.0 and -5.2 volts. The SPT7820 also provides a wide input voltage swing of ±2.0 volts. The SPT7820 is available in 28-lead ceramic sidebrazed DIP, PDIP and SOIC packages over the commercial, industrial and military temperature ranges. Contact the factory for availability of die and /883 versions. BLOCK DIAGRAM Analog Input Coarse A/D 4 Analog Prescaler T/H Amplifier Bank Decoding Network Digital Output 10 Successive Interpolation Stage i Successive Interpolation Stage i+1 Successive Interpolation Stage N ABSOLUTE MAXIMUM RATINGS (Beyond which damage may occur)1 25 °C Supply Voltages VCC ........................................................................... +6 V VEE ........................................................................... -6 V Input Voltages Analog Input ............................................... VFB≤VIN≤VFT VFT, VFB .............................................................. +3.0 V, -3.0 V Reference Ladder Current ..................................... 12 mA CLK Input .................................................................. VCC Note: Output Digital Outputs ......................................... +30 to -30 mA Temperature Operating Temperature ............................ -55 to +125 °C Junction Temperature1 .............................................. +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 TA=Tmin - Tmax, VCC=+5.0 V, VEE=-5.2 V, DVCC=+5.0 V, VIN=±2.0 V, VSB=-2.0 V, VST=+2.0 V, fCLK=20 MHz, 50% clock duty cycle, unless otherwise specified. PARAMETERS Resolution DC Accuracy (+25 °C) Integral Nonlinearity Differential Nonlinearity No Missing Codes Analog Input Input Voltage Range Input Bias Current Input Bias Current Input Resistance Input Resistance Input Capacitance Input Bandwidth +FS Error -FS Error Reference Input Reference Ladder Resistance Reference Ladder Tempco Timing Characteristics Maximum Conversion Rate Overvoltage Recovery Time Pipeline Delay (Latency) Output Delay Aperture Delay Time Aperture Jitter Time Acquisition Time Dynamic Performance Effective Number of Bits fIN=1 MHz fIN=3.58 MHz fIN=10.0 MHz TEST CONDITIONS TEST LEVEL MIN 10 SPT7820A TYP MAX MIN 10 SPT7820B TYP MAX UNITS Bits ±1.5 ±0.75 Guaranteed ±2.0 30 LSB LSB ±Full Scale 100 kHz Sample Rate V V VI V VI IV VI IV V V V V VI V VI V IV V V V V ±1.0 ±0.5 Guaranteed ±2.0 30 100 75 300 300 5 120 ±2.0 ±2.0 800 0.8 fCLK=1 MHz VIN=0 V TA=-55 to +125 °C TA=-55 to +125 °C 3 dB Small Signal 60 75 100 75 300 300 5 120 ±2.0 ±2.0 800 0.8 V 60 µA 75 µA kΩ kΩ pF MHz LSB LSB Ω Ω/°C MHz ns 1 Clock Cycle 18 ns ns ps-RMS ns fCLK=1 MHz 500 500 20 20 14 1 5 20 1 18 20 20 14 1 5 20 TA=+25 °C TA=+25 °C TA=+25 °C TA=+25 °C 9.2 8.8 7.5 8.7 8.3 7.0 Bits Bits Bits Typical thermal impedances (unsoldered, in free air): 28L sidebrazed DIP: θja = 50 °C/W, 28L plastic DIP: θja = 50 °C/W, 28L SOIC: θja = 100 °C/W. SPT7820 2 3/11/97 ELECTRICAL SPECIFICATIONS TA=Tmin - Tmax, VCC=+5.0 V, VEE=-5.2 V, DVCC=+5.0 V, VIN=±2.0 V, VSB=-2.0 V, VST=+2.0 V, fCLK=20 MHz, 50% clock duty cycle, unless otherwise specified. PARAMETERS Dynamic Performance Signal-To-Noise Ratio (Without Harmonics) fIN=1 MHz fIN=3.58 MHz fIN=10.0 MHz Harmonic Distortion fIN=1 MHz fIN=3.58 MHz fIN=10.0 MHz Signal-to-Noise and Distortion fIN=1 MHz TEST CONDITIONS TEST LEVEL MIN SPT7820A TYP MAX MIN SPT7820B TYP MAX UNITS TA=+25 °C TA=0-70, -25 to +85 °C TA=-55 to +125 °C* TA=+25 °C TA=0-70, -25 to +85 °C TA=-55 to +125 °C* TA=+25 °C TA=0-70, -25 to +85 °C TA=-55 to +125 °C* TA=+25 °C TA=0-70, -25 to +85 °C TA=-55 to +125 °C* TA=+25 °C TA=0-70, -25 to +85 °C TA=-55 to +125 °C* TA=+25 °C TA=0-70, -25 to +85 °) TA=-55 to +125 °C* I IV IV I IV IV I IV IV I IV IV I IV IV I IV IV I IV IV I IV IV I IV IV V V V VI VI I I IV IV VI VI IV IV IV I I I I V 57 55 52 56 54 52 50 47 43 57 54 50 56 53 50 46 45 45 55 52 48 54 51 48 44 43 41 60 58 55 58 56 54 53 50 46 60 57 53 58 55 52 48 47 47 57 54 52 49 53 51 49 47 44 40 54 51 47 53 50 47 43 42 42 52 49 45 51 48 45 41 40 38 57 55 52 55 53 51 49 46 42 57 54 50 55 52 49 45 44 44 54 dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB Degree TA=+25 °C TA=0-70, -25 to +85 °C TA=-55 to +125 °C* fIN=3.58 MHz TA=+25 °C TA=0-70, -25 to +85 °C TA=-55 to +125 °C* fIN=10.0 MHz TA=+25 °C TA=0-70, -25 to +85 °C TA=-55 to +125 °C* Spurious Free Dynamic Range TA=+25 °C, fIN=1 MHz Differential Phase TA=+25 °C, fIN=3.58 & 4.35 MHz Differential Gain TA=+25 °C, fIN=3.58 & 4.35 MHz Digital Inputs Logic 1 Voltage Logic 0 Voltage Maximum Input Current Low Maximum Input Current High Pulse Width Low (CLK) Pulse Width High (CLK) Digital Outputs Logic 1 Voltage Logic 0 Voltage Power Supply Requirements Voltages VCC DVCC -VEE Currents ICC DICC -IEE Power Dissipation Power Supply Rejection fCLK=1 MHz 55 52 47 44 67 0.2 0.5 2.4 0 0 20 20 2.4 0.6 4.75 4.75 -4.95 5.25 5.25 -5.45 145 55 57 1.3 4.75 4.75 -4.95 +5 +5 4.5 0.8 +20 +20 300 2.4 0 0 20 20 2.4 67 0.2 0.7 4.5 0.8 +20 +20 % V V µA µA ns 300 ns V 0.6 V 5.25 5.25 -5.45 145 55 57 1.3 V V V mA mA mA W LSB TA=+25 °C TA=+25 °C +5 +5 fCLK=1 MHz TA=+25 °C TA=+25 °C TA=+25 °C TA=+25 °C (5 V ±0.25 V, -5.2 ±0.25 V) 5.0 -5.2 118 40 40 1.0 1.0 5.0 -5.2 118 40 40 1.0 1.0 *Temperature tested /883 only. SPT7820 3 3/11/97 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 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. Figure 1A: Timing Diagram N N+1 N+2 tpwH tpwL CLK td Output Data N-2 N-1 Data Valid N Data Valid N+1 Figure 1B: Single Event Clock CLK td Output Data Data Valid Table I - Timing Parameters PARAMETERS td tpwH tpwL DESCRIPTION CLK to Data Valid Prop Delay CLK High Pulse Width CLK Low Pulse Width MIN 20 20 TYP 14 MAX 18 300 UNITS ns ns ns SPT7820 4 3/11/97 TYPICAL PERFORMANCE CHARACTERISTICS SNR vs Input Frequency 80 THD vs Input Frequency 80 70 70 fs = 20 MSPS Signal-to-Noise Ratio (dB) 60 Total Harmonic Distortion (dB) fs = 20 MSPS 60 50 50 40 40 30 30 20 100 101 102 20 100 101 102 Input Frequency (MHz) Input Frequency (MHz) SINAD vs Input Frequency 80 SNR, THD, SINAD vs Sample Rate 80 Signal-to-Noise and Distortion (dB) 70 70 SNR, THD 60 SNR, THD, SINAD (dB) fs =20 MSPS 60 50 50 fIN = 1 MHz 40 SINAD 40 30 30 20 100 101 102 20 100 101 102 Input Frequency (MHz) Sample Rate (MSPS) Spectral Response 0 SNR, THD, SINAD vs Temperature 65 fS = 20 MSPS fIN = 1 MHz 60 SNR SNR -30 SNR, THD, SINAD (dB) Amplitude (dB) THD 55 THD SINAD -60 50 -90 fS = 20 MSPS fIN = 1 MHz 45 -120 0 1 2 3 4 5 6 7 8 9 10 40 -25 0 +25 +50 +75 Input Frequency (MHz) Temperature (°C) SPT7820 5 3/11/97 TYPICAL INTERFACE CIRCUIT The SPT7820 requires few external components to achieve the stated operation and performance. Figure 2 shows the typical interface requirements when using the SPT7820 in normal circuit operation. The following section provides a description of the pin functions and outlines critical performance criteria to consider for achieving the optimal device performance. POWER SUPPLIES AND GROUNDING The SPT7820 requires -5.2 V and +5 V analog supply voltages. The +5 V supply is common to analog VCC and digital DVCC. A ferrite bead in series with each supply line is intended to reduce the transient noise injected into the analog VCC. These beads should be connected as closely as possible to the device. The connection between the beads and the SPT7820 should not be shared with any other device. Each power supply pin should be bypassed as closely as possible to the device. Use 0.1 µF for VEE and VCC, and 0.01 µF for DVCC (chip caps are preferred). AGND and DGND are the two grounds available on the SPT7820. These two internal grounds are isolated on the Figure 2 - Typical Interface Circuit R1 CLK (TTL) CLK device. The use of ground planes is recommended to achieve optimum device performance. DGND is needed for the DVCC return path (40 mA typical) and for the return path for all digital output logic interfaces. AGND and DGND should be separated from each other and connected together only at the device through a ferrite bead. A Schottky or hot carrier diode connected between AGND and VEE is required. The use of separate power supplies between VCC and DVCC is not recommended due to potential power supply sequencing latch-up conditions. Using the recommended interface circuit shown in figure 2 will provide optimum device performance for the SPT7820. VOLTAGE REFERENCE The SPT7820 requires the use of two voltage references: VFT and VFB. VFT is the force for the top of the voltage reference ladder (+2.5 V typ), VFB (-2.5 V typ) is the force for the bottom of the voltage reference ladder. Both voltages are applied across an internal reference ladder resistance of 800 Ω. The +2.5 V voltage source for reference VFT must be current limited to 20 mA maximum if a different driving circuit is used in place of the recommended reference circuit shown in figures 2 and 3. In addition, there are three reference 100 Ω (±2 V) VIN ± 2.5 V Max VIN COARSE A/D 4 D10 (Overrange) D9 (MSB) D I G IT A L O U DECODING NETWORK D8 D7 D6 D5 D4 D3 D2 D1 +5V C19 1 µF 2 + VIN IC1 6 VOUT +2.5 V VFT (REF-03) 4 GND 5 Trim 10 kΩ + 1 µF 30 kΩ C1 .01 µF C2 .01 µF VST R ANALOG PRESCALER 2R C3 .01 µF VRM 2R 2R 3 1 10 kΩ 2 4 +IC2 OP-07 8 7 - 5.2 V SUCCESSIVE INTERPOLATION STAGE # 1 .01 µF 30 kΩ +5 V .01 µF C4 .01 µF 2R VSB D0 (LSB) R SUCCESSIVE INTERPOLATION STAGE # N 6 -2.5 V VFB VCC + VCC VEE VEE 1 µF AGND C6 .1 µF C7 .1 µF C8 C9 C10 .01 µF C11 .01 µF Notes to prevent latch-up due to power sequencing: FB 1) D1 = Schottky or hot carrier diode, P/N IN5817. D1 2) FB = Ferrite bead, Fair Rite P/N 2743001111 10 µF to be mounted as close to the device as possible. The ferrite bead to the ADC connection should not be shared with any other device. 3) C1-C11 = Chip cap (recommended) mounted as close to the device's pin as possible. 4) Use of a separate supply for VCC and DVCC is not recommended. -5.2 V (Analog) 5) R1 provides current limiting to 45 mA. 6) C6, C7, C8 and C9 should be ten times larger than C10 and C11. 7) C8 = C9 = a 0.1 µF cap in parallel with a 4.7 µF cap. 10 µF + + FB AGND +5 V (Analog) FB DGND DGND AGND DVCC DVCC C5 .01 µF DGND SPT7820 6 3/11/97 ladder taps (VST, VRM and VSB). VST is the sense for the top of the reference ladder (+2.0 V), VRM is the midpoint of the ladder (0.0 V typ) and VSB is the sense for the bottom of the reference ladder (-2.0 V). The voltages seen at VST and VSB are the true full scale input voltages of the device when VFT and VFB are driven to the recommended voltages (+2.5 V and -2.5 V typical respectively). These points should be used to monitor the actual full scale input voltage of the device and should not be driven to the expected ideal values as is commonly done with standard flash converters. When not being used, a decoupling capacitor of .01 µF (chip cap preferred) connected to AGND from each tap is recommended to minimize high frequency noise injection. Figure 3 - Analog Equivalent Input Circuit VCC ANALOG INPUT VIN is the analog input. The full scale input range will be 80% of the reference voltage or ±2 volts with VFB=-2.5 V and VFT=+2.5 V. The drive requirements for the analog inputs are minimal when compared to conventional Flash converters due to the SPT7820’s extremely low input capacitance of only 5 pF and very high input resistance of 300 kΩ. For example, for an input signal of ±2 V p-p with an input frequency of 10 MHz, the peak output current required for the driving circuit is only 628 µA. CLOCK INPUT The SPT7820 is driven from a single-ended TTL input (CLK). The CLK pulse width (tpwH) must be kept between 20 ns and 300 ns to ensure proper operation of the internal track-andhold amplifier. (See timing diagram.) When operating the SPT7820 at sampling rates above 3 MSPS, it is recommended that the clock input duty cycle be kept at 50% but performance will not be degraded if kept within the range of 40-60%. The analog input signal is latched on the rising edge of the CLK. The clock input must be driven from fast TTL logic (VIH ≤4.5 V, TRISE +2.0 V + 1/2 LSB +2.0 V -1 LSB 0.0 V -2.0 V +1 LSB