SPT7755

SPT7755 8-BIT, 750 MSPS, FLASH A/D CONVERTER OCTOBER 2002 FEATURES • • • • • • 1:2 Demuxed ECL compatible outputs Wide input bandwidth – 900 MHz Low input capacitance – 15 pF Metastable errors reduced to 1 LSB Monolithic for low cost Gray code output APPLICATIONS • • • • Digital oscilloscopes Transient capture Radar, EW, ECM Direct RF down-conversion GENERAL DESCRIPTION The SPT7755 is a full parallel (flash) analog-to-digital conver ter capable of digitizing full scale (0 to –2 V) inputs into eight-bit digital words at an update rate of 750 MSPS. The ECL-compatible outputs are demultiplexed into two separate output banks, each with differential data ready outputs to ease the task of data capture. The SPT7755’s wide input bandwidth and low capacitance eliminate the need for external track-and-hold amplifiers for most applications. A proprietar y decoding scheme reduces metastable errors to the 1 LSB level. The SPT7755 operates from a single – 5.2 V supply, with a nominal power dissipation of 5.5 W. The SPT7755 is available in an 80-lead surface-mount MQuad package over the industrial temperature range (–25 °C to +85 °C). BLOCK DIAGRAM Analog VRT Input Preamp Comparator 256 CLK CLK CLOCK BUFFER DEMUX CLOCK BUFFER 255 D8 (OVR) D7 (MSB) D6 DRB (DATA READY) D8B D7B D6B D5B D4B D3B D2B DRB (DATA READY) D8B (OVR) D7B (MSB) D5B D6B 152 256 TO 8 Bit Decoder With Metastable Error Correction ECL Output Buffers And Latches 151 D4B D3B D2B D1B D0B (LSB) DRA (DATA READY) DRA (DATA READY) D8A (OVR) D7A (MSB) D5A D4A D3A D2A D1A D0A (LSB) D6A D5 1:2 DEMULTIPLEXER 128 D1B D0B VRM 127 D4 D8A D7A D6A D5A D4A D3A D2A D1A D0A 64 D3 63 D2 2 D1 1 D0 (LSB) VRB BANK A BANK B ABSOLUTE MAXIMUM RATINGS (Beyond which damage may occur)1 25 °C Supply Voltages Negative Supply Voltage (VEE TO GND) –7.0 to +0.5 V Ground Voltage Differential .................... –0.5 to +0.5 V Input Voltage Analog Input Voltage ............................... +0.5 V to VEE Reference Input Voltage .......................... +0.5 V to VEE Digital Input Voltage ................................ +0.5 V to VEE Reference Current VRT to VRB ........................... 35 mA Output Digital Output Current ............................... 0 to –28 mA Temperature Operating Temperature, ambient ............ –25 to +85 °C case .......................... +125 °C junction ...................... +150 °C Lead Temperature, (soldering 10 seconds) ...... +300 °C Storage Temperature ............................ –65 to +150 °C Note: 1. Operation at any Absolute Maximum Rating is not implied. See Electrical Specifications for proper nominal applied conditions in typical applications. ELECTRICAL SPECIFICATIONS TJ = TC = TA = +25 °C , VEE=–5.2 V, VRB=–2.0 V, VRM=–1.0 V, VRT=0.00 V, ƒCLK=750 MHz, Duty Cycle=50%, unless otherwise specified. PARAMETERS Resolution DC Accuracy Integral Linearity Error (ILE) Differential Linearity Error (DLE) No Missing Codes Analog Input Input Voltage Range Input Bias Current Input Resistance Input Capacitance Input Bandwidth Small Signal Large Signal Offset Error VRT Offset Error VRB Input Slew Rate Clock Synchronous Input Currents Reference Input Ladder Resistance Reference Bandwidth Timing Characteristics Maximum Sample Rate Aperture Jitter Acquisition Time Clock to Data Delay CLK to Data Ready Delay Dynamic Performance Signal-To-Noise Ratio (without Harmonics) ƒIN = 50 MHz ƒIN = 250 MHz Total Harmonic Distortion ƒIN = 50 MHz ƒIN = 250 MHz Signal-to-Noise and Distortion ƒIN = 50 MHz ƒIN = 250 MHz TEST CONDITIONS TEST LEVEL MIN SPT7755A TYP MAX 8 MIN SPT7755B TYP MAX UNITS 8 Bits +1.5 +1.5 Guaranteed LSB LSB ƒCLK = 100 kHz ƒCLK = 100 kHz I I –1.0 –0.85 Guaranteed +1.0 +0.95 –1.5 –0.95 VIN=0 V Over Full Input Range I I V V V V IV IV V V I V I V V IV IV VRB .75 15 15 900 500 –30 –30 5 2 60 80 30 VRT 2.0 VRB .75 15 15 900 500 VRT 2.0 V mA kΩ pF MHz MHz mV mV V/ns µA Ω MHz MHz ps ps ns ns +30 +30 –30 –30 5 2 60 80 30 +30 +30 750 0.9 1.25 2 250 1.4 1.75 1.9 2.25 750 0.9 1.25 2 250 1.4 1.75 1.9 2.25 I I I I I I 46 44 –45 –37 43 36 44 42 –43 –35 41 34 dB dB dBc dBc dB dB 2 SPT7755 October 2002 ELECTRICAL SPECIFICATIONS TJ = TC = TA = +25 °C , VEE=–5.2 V, VRB=–2.0 V, VRM=–1.0 V, VRT=0.00 V, ƒCLK=750 MHz, Duty Cycle=50%, unless otherwise specified. PARAMETERS Dynamic Performance Spurious Free Dynamic Range ƒIN = 50 MHz ƒIN = 250 MHz Digital Inputs Input High Voltage (CLK, CLK) Input Low Voltage (CLK, CLK) Clock Pulse Width High (tPWH) Clock Pulse Width Low (tPWL) Digital Outputs Logic 1 Voltage Logic 0 Voltage Rise Time Fall Time Power Supply Requirements Voltage VEE Current IEE Power Dissipation TEST CONDITIONS TEST LEVEL MIN SPT7755A TYP MAX MIN SPT7755B TYP MAX UNITS I I 48 40 44 36 dB dB I I I I I I V V IV I I –1.1 0.67 0.67 –1.1 –0.7 –1.8 0.5 0.5 –0.9 –1.8 450 450 –5.2 1.05 5.5 –1.5 –1.1 0.67 0.67 –1.1 –1.5 –0.7 –1.8 0.5 0.5 –0.9 –1.8 450 450 –5.2 1.05 5.5 –1.5 V V ns ns V V ps ps –1.5 20% to 80% 20% to 80% –4.95 –5.45 1.2 6.25 –4.95 –5.45 V 1.2 A 6.25 W Typical Thermal Impedance: θJC = +4 °C/W. 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. Unless otherwise noted, all test are pulsed tests; therefore, TJ = TC = TA. 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. 3 SPT7755 October 2002 GENERAL DESCRIPTION The SPT7755 is one of the fastest monolithic 8-bit parallel flash A/D converters available today. The nominal conversion rate is 750 MSPS and the analog bandwidth is in excess of 900 MHz. A major advance over previous flash converters is the inclusion of 256 input preamplifiers between the reference ladder and input comparators (see block diagram). This not only reduces clock transient kickback to the input and reference ladder due to a low AC beta, but also reduces the effect of the dynamic state of the input signal on the latching characteristics of the input comparators. The preamplifiers act as buffers and stabilize the input capacitance so that it remains constant over different input voltage and frequency ranges and therefore Figure 1 – SPT7755 Typical Interface Circuit DRB VIN** 50 W VIN VIN DRB DRA makes the part easier to drive than previous flash converters. The preamplifiers also add a gain of two to the input signal so that each comparator has a wider overdrive or threshold range to “trip” into or out of the active state. This gain reduces metastable states that can cause errors at the output. The SPT7755 has true differential analog and digital data paths from the preamplifiers to the output buffers (Current Mode Logic) for reducing potential missing codes while rejecting common mode noise. Signature errors are also reduced by careful layout of the analog circuitry. The output drive capability of the device can provide full ECL swings into 50 Ω loads. U3 DRB (DATA READY) DRB (DATA READY) DRA (DATA READY) 50 W 50 W DRA U3 DRA (DATA READY) –2.0 V Pulldown (Digital) VRTF R 22 W VRTS D8B (OVR) D7B (MSB) D6B D5B D4B D3B D2B D1B D0B (LSB) D8A (OVR) D7A (MSB) D6A D5A D4A D3A D2A D1A D0A (LSB) + U1 – R * VRM Convert U2 CLK CLK 50 W 50 W 50 W 50 W AGND DGND VEE + –2.0 V Reference – 22 W 2N2907 U1 VRBS VRBF * –5.2 V –5.2 V .1 µF FB = Ferrite bead –2.0 V Pulldown (Digital) –2 V Pulldown (Analog) U1 = OP291 or equivalent with low offset/noise. R = 1 kW; 0.1% matched. = AGND = DGND U2 = ON Semiconductor ECLinPS LITE, MC10EL16, differential receiver with 250 ps (typ) propagation delay. U3 = MC10EL16 or MC100EL16. * = 10 µF Tantalum Capacitor and 0.1 µF Chip Capacitor * –5.2 V FB ** = Care must be taken to avoid exceeding the maximum rating for the input, especially during power up sequencing of the analog input driver. 4 SPT7755 October 2002 TYPICAL INTERFACE CIRCUIT The circuit in figure 1 is intended to show the most elaborate method of achieving the least error by correcting for integral linearity, input induced distor tion, and power supply/ground noise. This is achieved by the use of external reference ladder tap connections, input buffer, and supply decoupling. Please contact the factor y for the SPT7755 evaluation board application note that contains more details on interfacing the SPT7755. The function of each pin and external connections to other components is as follows: VEE, AGND, DGND VEE is the supply pin with AGND as ground for the device. The power supply pins should be bypassed as close to the device as possible with at least a .01 µF ceramic capacitor. A 10 µF tantalum can also be used for low frequency suppression. DGND is the ground for the ECL outputs and is to be referenced to the output pulldown voltage and appropriately bypassed as shown in figure 1. VIN (ANALOG INPUT) There are two analog input pins that are tied to the same point internally. Either one may be used as an analog input sense and the other for input force. This is convenient for testing the source signal to see if there is sufficient drive capability. The pins can also be tied together and driven by the same source. The SPT7755 is superior to similar devices due to a preamplifier stage before the comparators. This makes the device easier to drive because it has constant capacitance and induces less slew rate distor tion. CLK, CLK (CLOCK INPUTS) The clock inputs are designed to be driven differentially with ECL levels. The duty cycle of the clock should be kept at 50% to avoid causing larger second harmonics. If this is not impor tant to the intended application, then duty cycles other than 50% may be used. D0 TO D8, DR, DR, (A AND B) The digital outputs can drive 50 Ω to ECL levels when pulled down to –2 V. When pulled down to –5.2 V, the outputs can drive 130 Ω to 1 kΩ loads. All digital outputs are grey code with the coding as shown in table I. CADEKA recommends using differential receivers on the outputs of the data ready lines to ensure the proper output rise and fall times. VRBF, VRBS, VRTF, VRTS, VRM (REFERENCE INPUTS) There are two reference inputs and one external reference voltage tap. These are –2 V (VRB force and sense), midtap (VRM) and AGND (VRT force and sense). The reference pins and tap can be driven by op amps as shown in figure 1 or VRM may be bypassed for limited temperature operation. These voltage inputs can be bypassed to AGND for fur ther noise suppression if so desired. Table I – Output Coding VIN >–0.5 LSB –0.5 LSB –1.5 LSB • • • –1.0 V • • • –2.0 V +0.5 LSB