HI5767EVAL2 Evaluation Board User’s Manual TM Application Note January 1999 AN9762 Description converter is adjustable by way of a potentiometer. This allows the effects of sample clock duty cycle on the HI5767 to be observed. The HI5767EVAL2 evaluation board allows the circuit designer to evaluate the performance of the Intersil HI5767 monolithic 10-bit 20/40/60MSPS analog-to-digital converter (ADC). As shown in the Evaluation Board Functional Block Diagram, the evaluation board includes sample clock generation circuitry, a single-ended to differential analog input RF transformer configuration, an on board external variable reference voltage generator and a digital data output header/connector. The digital data outputs are conveniently provided for easy interfacing to a ribbon connector or logic probes. In addition, the evaluation board includes some prototyping area for the addition of user designed custom interfaces or circuits. The analog input signal is also connected through an SMA type RF connector, J1, and applied to a single-ended to differential analog input RF transformer. This input is AC-coupled and terminated in 50Ω allowing for connection to most laboratory signal generators. The converters’ digital data outputs along with two phases of the sample clock (CLK and CLK) are provided at the output header/connector. With this output configuration the digital data output transitions seen at the I/O header/connector are essentially time aligned with the rising edge of the sampling clock (CLK) or the falling edge of the out of phase sampling clock (CLK). The sample clock generator circuit accepts the external sampling signal through an SMA type RF connector, J2. This input is AC-coupled and terminated in 50Ω allowing for connection to most laboratory signal generators. In addition, the duty cycle of the clock driving the A/D Refer to the component layout and the evaluation board electrical schematic for the following discussions. Evaluation Board Functional Block Diagram SAMPLE CLOCK INPUT J2 50Ω +5VD BIAS TEE CLK CLOCK OUT CLK 1.2V BANDGAP VOLTAGE REFERENCE ANALOG INPUT +2.5V VAR GAIN CLK VREFIN VREFOUT RF TRANSFORMER VIN+ J1 DIGITAL DATA OUT (D0 - D9) 10 D0-D9 VINHI5767 DGND AGND +5VD +5VA -5VA 3-1 1-888-INTERSIL or 321-724-7143 | Intersil and Design is a trademark of Intersil Corporation. | Copyright © Intersil Corporation 2000 Application Note 9762 External Reference Voltage Generator, VREFOUT and VREFiN The HI5767 has an internal reference voltage generator, therefore no external reference voltage is required. The evaluation board, however, offers the ability to use the converters’ internal reference voltage, VREFOUT, or the on board external variable reference voltage generator. The external variable reference voltage circuitry is implemented using the Intersil ICL8069 low voltage, 1.2V, bandgap reference (D1) sourcing a non-inverting variable gain operational amplifier circuit based on the Intersil HA5127 ultra-low noise precision operational amplifier (U1). Potentiometer VR1 is used to adjust the output voltage level of this external voltage reference. With this the user is able to observe the effects of reference voltage variations on the converters performance. Turning VR1 in a clockwise (CW) direction will decrease the external reference voltage while turning VR1 in a counterclockwise (CCW) direction will decrease the external reference voltage. Selection of the reference voltage to be used by the converter is accomplished by placing the P3 header jumper across the appropriate pins. The converters’ internal reference voltage generator, VREFOUT, must be connected to VREFIN when using the converters internal reference and is selected by placing the P3 header jumper across P3-2 and P3-3. Alternately, if it is desired to use the on board external variable reference voltage generator, selection of this option is done by placing the P3 header jumper across P3-1 and P3-2. See Appendix A, Board Layout for the location of the P3 reference voltage selection header. Analog Input The fully differential analog input of the HI5767 A/D can be configured in various ways depending on the signal source and the required level of performance. Differential Analog Input Configuration A fully differential connection (Figure 1) will yield the best performance from the HI5767 A/D converter. Since the HI5767 is powered off a single +5V supply, the analog input must be biased so it lies within the analog input common mode voltage range of 0.25V to 4.75V. Figure 2 illustrates the differential analog input common mode voltage, VDC, range that the converter will accommodate. The performance of the converter does not change significantly with the value of the analog input common mode voltage. +5V VIN+ 0.5VP-P VINVDC = 4.75V +5V FIGURE 2A. VIN+ VIN0.5VP-P 0.25V < VDC < 4.75V FIGURE 2B. VIN+ VIN0.5VP-P VDC = 0.25V 0V 0V FIGURE 2C. FIGURE 2. DIFFERENTIAL ANALOG INPUT COMMON MODE VOLTAGE RANGE A DC bias voltage source, VDC, equal to 3.0V (typical), is made available to the user to help simplify circuit design when using an AC coupled differential input. This low output impedance voltage source is not designed to be a reference but makes an excellent DC bias source and stays well within the analog input common mode voltage range over temperature. For the AC coupled differential input (Figure 1) and with VREFIN connected to VREFOUT, full scale is achieved when the VIN and -VIN input signals are 0.5VP-P, with -VIN being 180 degrees out of phase with VIN . The converter will be at positive full scale when the VIN+ input is at VDC + 0.25V and the VIN- input is at VDC - 0.25V (VIN+ - VIN- = +0.5V). Conversely, the converter will be at negative full scale when the VIN+ input is equal to VDC - 0.25V and VIN- is at VDC + 0.25V (VIN+ - VIN- = -0.5V). It should be noted that overdriving the analog input beyond the ±0.5V fullscale input voltage range will not damage the converter as long as the overdrive voltage stays within the converters analog supply voltages. In the event of an overdrive condition the converter will recover within one sample clock cycle. VIN+ VIN HI5767 VDC -VIN VIN - FIGURE 1. AC COUPLED DIFFERENTIAL INPUT 3-2 A single-ended input will give better overall system performance if it is first converted to differential before driving the HI5767. An RF transformer can be connected to the HI5767 input to provide the single-ended to differential conversion. The particular transformer used will depend on the input voltage level, the impedance desired, and the input frequency range. The transformer will tend to have a bandpass response resulting in low and high frequency Application Note 9762 cutoffs. This is the type of single-ended to differential conversion circuitry that is provided on the HI5767EVAL2 evaluation board (refer to the HI5767EVAL2 evaluation board parts layout and the electrical schematics). The HI5767EVAL2 evaluation board provides the singleended to differential analog front-end for converting the typical laboratory signal generators 50Ω single-ended output to a differential input signal for the converters differential-indifferential-out sample-and-hold front end. The input of this analog front-end, RF SMA connector J1, is AC coupled and provides a termination impedance of 50Ω. The Mini-Circuits T4-1 transformer, T1, provides a 1dB passband from 2MHz to 100MHz. Since this transformer has a 1:4 primary to secondary impedance ratio the 200Ω secondary impedance, created by the series resistance of R9 and R10, is now transformed to 50Ω at the transformer primary side (200/4 = 50). Alternate transformers could be used with minor modifications to the input circuit. For example, if one desired a narrower input frequency range than that provided by the Mini-Circuits T4-1 transformer one could replace the T4-1 with a Mini-Circuits TMO2.5-6T. The TMO2.5-6T transformer provides a 1dB passband from 0.05MHz to 20MHz and has a 1:2.5 primary to secondary impedance ratio. With this, the 200Ω secondary load (two 100Ω resistors, R9 and R10, connected across the transformer secondary) is now transformed to 80Ω (200/2.5 = 80) at the transformer primary side input. In order to achieve a 50Ω input impedance at the analog input connector, J1, it would be necessary to install a 130Ω resistor in the R3 (A/R) location, i.e., the impedance now seen looking into the J1 SMA connector is 130Ω (R3) in parallel with 80Ω for an effective impedance of 50Ω. When using transformer coupling, care should be exercised in the area of impedance matching or undesirable distortion components could result from mismatching and affect the overall measured performance of the converter. Evaluation Board Layout and Power Supplies The HI5767 evaluation board is a four layer board with a layout optimized for the best performance of the converter. This application note includes an electrical schematic of the evaluation board, a component parts list, a component placement layout drawing and reproductions of the various board layers used in the board stack-up. The user should feel free to copy the layout in their application. The HI5767 monolithic A/D converter has been designed with separate analog and digital supply and ground pins to keep digital noise out of the analog signal path. The evaluation board provides separate low impedance analog and digital ground planes on layer 2. Since the analog and digital ground planes are connected together at a single 3-3 point where the power supplies enter the board, DO NOT tie them together back at the power supplies. The analog and digital supplies are also kept separate on the evaluation board and should be driven by clean linear regulated supplies. The external power supplies are hooked up with the twisted pair wires soldered to the plated through holes marked +5VAIN, +5VA1IN, -5VAIN, +5VDIN, +5VD1IN, +5VD2IN, AGND and DGND near the prototyping area. +5VDIN, +5VD1IN and +5VD2IN are digital supplies and are returned to DGND. +5VAIN, +5VAIN1 and -5VAIN are the analog supplies and are returned to AGND. Table 1 lists the operational supply voltages, typical current consumption and the evaluation board circuit function being powered. Single supply operation of the converter is possible but the overall performance of the converter may degrade. TABLE 1. HI5767EVAL2 EVALUATION BOARD POWER SUPPLIES POWER SUPPLY NOMINAL VALUE CURRENT (TYP) FUNCTION(S) SUPPLIED +5VAIN 5.0V ±5% 6mA External Reference Voltage Operational Amplifier, Bandgap Reference -5VAIN -5.0V ±5% 5mA External Reference Voltage Operational Amplifier +5VA1IN 5.0V ±5% 50mA A/D AVCC +5VDIN 5.0V ±5% 63mA Sample Clock Generation +5VD1IN 5.0V ±5% 20mA A/D DVCC1 +5VD2IN 3.0V ±10% 5mA A/D DVCC2 Sample Clock Driver In order to ensure rated performance of the HI5767, the duty cycle of the sample clock should be held at 50% ±5%. It must also have low phase noise and operate at standard TTL levels. It can be difficult to find a low phase noise generator that will provide a 60MHz squarewave at TTL logic levels. Consequently, the HI5767EVAL2 evaluation board is designed with a logic inverter (U5) acting as a voltage comparator to generate the sampling clock for the HI5767 when a sinewave (<±1.5V) is applied to the AC-coupled, 50Ω terminated CLK input through SMA type RF connector, J2, of the evaluation board. The sample clock sinewave is AC coupled into the input of the inverter and a discrete bias tee is used to bias the sinewave around the trigger level of the inverter’s input. A potentiometer (VR2) varies the DC bias voltage added to the sinewave input allowing the user to adjust the duty cycle of the sampling clock to obtain the best performance from the ADC and to evaluate the effects of sample clock duty cycle on the performance of the converter. The trigger level for the sample clock input to the HI5767 Application Note 9762 converter is approximately 1.5V. Therefore, the duty cycle of the sampling clock should be measured at the 1.5V trigger level of the HI5767 sample clock input pin. The sinewave to logic level comparator drives a series of additional inverters that provide isolation between the three sample clocks used on the evaluation board. One clock is used to drive the converter sample clock input pin and the other two provide CLK and CLK at the data output header/connector, P2. The clock/data relationship at the P2 output connector is as follows. CLK has rising edges aligned with digital data transitions and CLK has rising edges aligned mid-bit. The data corresponding to a particular analog input sample will be available at the digital outputs of the HI5767 after the data latency (7 cycles) plus the HI5767 digital data output delay. The sample clock and digital output data signals are made available through two connectors contained on the evaluation board. Line drivers are not provided for the digital output data and it should be pointed out that the load presented to the converter digital output data signals, D0 - D9, should not exceed the data sheet CMOS drive limits and a load capacitance of 10pF. The P1 96-pin I/O connector allows the evaluation board to be interfaced to the DSP evaluation boards available from Intersil. The digital output data and sample clock can also be accessed by clipping the test leads of a logic analyzer or data acquisition system onto the header/connector pins of connector P2. The A/D converters OE control input pin allows the digital output data bus of the converter to be switched to a threestate high impedance mode. This feature enables the testing and debugging of systems which are utilizing one or more converters. This three-state control signal is not intended for use as an enable/disable function on a common data bus and could result in possible bus contention issues. The A/D converters OE control input pin is controlled by the installation or removal of a shunt, JP1, contained on the evaluation board. Installation of JP1 forces the OE control input pin low for normal operation while removal of JP1 allows the digital output data bus of the converter to be switched to a three-state high impedance mode. HI5767 Performance Characterization Dynamic testing is used to evaluate the performance of the HI5767 A/D converter. Among the tests performed are Signal-to-Noise and Distortion Ratio (SINAD), Signal-toNoise Ratio (SNR), Total Harmonic Distortion (THD), Spurious Free Dynamic Range (SFDR) and Intermodulation Distortion (IMD). Figure 4 shows the test system used to perform dynamic testing on high-speed ADCs at Intersil. The clock (CLK) and analog input (VIN) signals are sourced from low phase noise HP8662A synthesized signal generators that are phase 3-4 locked to each other to ensure coherence. The output of the signal generator driving the ADC analog input is bandpass filtered to improve the harmonic distortion of the analog input signal. The comparator on the evaluation board will convert the sine wave CLK input signal to a square wave at TTL logic levels to drive the sample clock input of the HI5767. The ADC data is captured by a logic analyzer and then transferred over the GPIB bus to the PC. The PC has the required software to perform the Fast Fourier Transform (FFT) and do the data analysis. Coherent testing is recommended in order to avoid the inaccuracies of windowing. The sampling frequency and analog input frequency have the following relationship: fI/fS = M/N, where fI is the frequency of the input analog sinusoid, fS is the sampling frequency, N is the number of samples, and M is the number of cycles over which the samples are taken. By making M an integer and odd number (1, 3, 5, ...) the samples are assured of being nonrepetitive. Refer to the HI5767 data sheet for a complete list of test definitions and the results that can be expected using the evaluation board with the test setup shown. Evaluating the part with a reconstruction DAC is only suggested when doing bandwidth or video testing. HP8662A HP8662A REF BANDPASS FILTER VIN CLK COMPARATOR VIN HI5767 CLK DIGITAL DATA OUTPUT HI5767EVAL2 EVALUATION BOARD 14 DAS9200 GPIB PC FIGURE 3. HIGH-SPEED A/D PERFORMANCE TEST SYSTEM Application Note 9762 Appendix A Board Layout FIGURE 4. HI5767EVAL2 EVALUATION BOARD PARTS LAYOUT (NEAR SIDE) FIGURE 5. HI5767EVAL2 EVALUATION BOARD COMPONENT NEAR SIDE (LAYER 1) 3-5 Application Note 9762 Appendix A Board Layout (Continued) FIGURE 6. HI5767EVAL2 EVALUATION BOARD GROUND PLANE LAYER (LAYER 2) FIGURE 7. HI5767EVAL2 EVALUATION BOARD POWER PLANE LAYER (LAYER 3) 3-6 Application Note 9762 Appendix A Board Layout (Continued) FIGURE 8. HI5767EVAL2 EVALUATION BOARD COMPONENT FAR SIDE (LAYER 4) FIGURE 9. HI5767EVAL2 EVALUATION BOARD PARTS LAYOUT (FAR SIDE) 3-7 C32 + 4.7µF C28 0.1µF D0 - D9, CLK4 (CLK) TO P1 U5 1 +5VD1 2 C24 4.7µF 3 4 C25 0.1µF C9 0.1µF 5 6 EXT VREF P3 7 8 9 VIN+ 10 VIN- 11 VDC 12 13 +5VA1 + 14 + DVCC1 D0 DGND1 D1 DVCC1 D2 DGND1 D3 AVCC D4 AGND DVCC2 VREFIN VREFOUT HI5767 CLK DGND2 VIN+ D5 VIN- D6 VDC D7 AGND D8 AVCC D9 OE DFS 28 27 P2 D0 1 D1 3 2 6 23 D2 5 D3 7 22 D4 9 10 21 D5 11 12 20 D6 13 14 19 D7 15 16 18 D8 17 18 17 D9 19 20 21 22 23 24 26 25 24 CLK1 4 8 16 15 CLK4 R6 R5 C26 4.7µF C29 0.1µF C30 C27 C35 0.1µF 0.1µF 4.7µF C33 0.1µF JP1 4.99K 4.99K +5VD CLK3 JP2 Application Note 9762 + Appendix B Schematic Diagrams 3-8 +5VD2 Application Note 9762 Appendix B Schematic Diagrams J1 (Continued) ZIN:ZOUT (1:4) C11 0.1µF C10 0.1µF VIN+ VIN R3 A/R R9 100 T1 6 1 2 R4 0 T4-1-KK81 4 3 C31 0.1µF VDC C12 0.1µF R10 100 5 - NC VINC13 0.1µF SINGLE-ENDED TO DIFFERENTIAL (TRANSFORMER) ANALOG FRONT END 3-9 Application Note 9762 Appendix B Schematic Diagrams (Continued) +5VA +5VA + C4 4.7µF C3 0.1µF R2 4.99K 3 8 4 NC + 8 V+ NC NC D1 ICL8069CCBA 2 C6 0.1µF C23 4.7µF 7 1.2V + C1 4.7µF + C8 0.1µF 1 - V5 U1 HA5127 4 C2 0.1µF 6 -5VA C5 0.1µF R7 499 R1 249 VR1 1.0K C21 + 4.7µF 1(CCW) 2 VREF 3(CW) VREF EXTERNAL REFERENCE VOLTAGE GENERATION CIRCUIT 3-10 R8 0 2.5V + C7 0.1µF C22 4.7µF EXT VREF Application Note 9762 Appendix B Schematic Diagrams (Continued) +5VD + C42 0.1µF J2 C14 C34 4.7µF 0.1µF U3 C38 0.1µF 13 AC04 U7 1 12 14 2 CLK1 CLK IN R12 56.2 7 L1 1.5µH U7 9 VR2 1.0K (CLK) 8 1(CCW) 2 +5VD + AC04 AC04 3(CW) C40 C41 4.7µF 0.1µF U7 11 C37 0.1µF R11 100 10 CLK3 AC04 U7 3 (CLK) 4 AC04 AGND TEST POINT TP1 U7 5 DGND TEST POINT TP3 TP2 6 CLK4 (CLK) AC04 TP4 E1 E9 E10 E2 FB5 +5VAIN FB1 +5VA + AGND C44 4.7µF C43 0.1µF +5VDIN + DGND (REFERENCE VOLTAGE GENERATOR OP-AMP, BANDGAP REFERENCE) E11 E12 E5 + AGND E7 +5VD1IN C45 C46 4.7µF 0.1µF E3 FB4 C36 4.7µF 3-11 C39 0.1µF C20 C19 4.7µF 0.1µF +5VD1 (A/D DVCC1) E4 FB2 -5VA + + DGND AGND AND DGND TIE TOGETHER AT A SINGLE POINT WHERE THE POWER SUPPLIES ENTER THE PWB -5VAIN AGND FB3 +5VA1 (A/D AVCC) E8 +5VD (SAMPLE CLOCK GENERATOR) E6 FB6 +5VA1IN C16 C15 4.7µF 0.1µF (REFERENCE VOLTAGE GENERATOR OP AMPS, BANDGAP REFERENCE) +5VD2IN DGND + C18 C17 4.7µF 0.1µF +5VD2 (+5V/+3V) (A/D DVCC2) Application Note 9762 Appendix B Schematic Diagrams (Continued) P1C D1 D2 D4 D6 D8 CLK4 (CLK) C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 D0 - D9, CLK4 (CLK) 96 PIN I/O CONNECTOR 3-12 P1A D0 D3 D5 D7 D9 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15 A16 A17 A18 A19 A20 A21 A22 A23 A24 A25 A26 A27 A28 A29 A30 A31 A32 Application Note 9762 Appendix C Parts List REFERENCE DESIGNATOR QTY --- 1 Printed Wiring Board R7 1 499Ω, 1/10W 805 Chip, 1% DESCRIPTION REFERENCE DESIGNATOR QTY L1 1 1.5µH Chip Inductor, 1210 Case FB1-6 6 10µH Ferrite Bead DESCRIPTION R12 1 56.2Ω, 1/10W 805 Chip, 1% J1, J2 2 SMA Straight Jack PCB Mount R3 1 A/RΩ, 1/10W 805 Chip, 1% --- 4 Protective Bumper JP1, JP2 2 1x2 Header R9, R10, R11 3 100Ω, 1/10W 805 Chip, 1% JPH1, JPH2 2 1x2 Header Jumper R4, R8 2 0.0Ω, 1/10W 805 Chip, 1% P3 1 1x3 Header PH3 1 1x2 Header Jumper R2, R5, R6 3 4.99kΩ, 1/4W 805 Chip, 5% P2 1 2x12 Header TP1, TP2, TP3, TP4 4 Test Point R1 1 249Ω, 1/10W 805 Chip, 1% U2 1 Intersil HI5767 10-Bit 20/40/60MSPS A/D Converter with Internal Voltage Reference U1 1 Intersil HA9P5127-5 8.5MHz, Ultra-Low Noise Precision Operational Amplifier U3 1 Intersil CD74HC04M High Speed CMOS Logic Hex Inverter D1 1 Intersil ICL8069CCBA Low Voltage Bandgap Reference P1 6 64-Pin Eurocard RT Angle Receptacle VR1, VR2 2 1kΩ Trim Pot C1, C4, C14, C16, C18, C20, C21, C22, C23, C24, C26, C32, C35, C36, C40, C44, C46 17 4.7µF Chip Tant Cap, 10WVDC, 20%, EIA Case A C2, C3, C5, C6, C7, C8, C9, C10, C11, C12, C13, C15, C17, C19, C25, C27, C28, C29, C30, C31, C33, C34, C37, C38, C39, C41, C42, C43, C45 29 T1 1 3-13 0.1µF Cer Cap, 50WVDC, 10%, 805 Case, Y5V Dielectric RF Transformer, 1:4 Primary to Secondary Impedance Ratio Application Note 9762 Appendix D HI5767 Theory of Operation The HI5767 is a 10-bit fully differential sampling pipeline A/D converter with digital error correction logic. Figure 10 depicts the circuit for the front end differential-in-differential-out sample-and-hold (S/H). The switches are controlled by an internal sampling clock which is a non-overlapping two phase signal, φ1 and φ2 , derived from the master sampling clock. During the sampling phase, φ1 , the input signal is applied to the sampling capacitors, CS . At the same time the holding capacitors, CH , are discharged to analog ground. At the falling edge of φ1 the input signal is sampled on the bottom plates of the sampling capacitors. In the next clock phase, φ2 , the two bottom plates of the sampling capacitors are connected together and the holding capacitors are switched to the op amp output nodes. The charge then redistributes between CS and CH completing one sample-and-hold cycle. The front end sample-and-hold output is a fully-differential, sampled-data representation of the analog input. The circuit not only performs the sample-and-hold function but will also convert a single-ended input to a fully-differential output for the converter core. During the sampling phase, the VIN pins see only the on-resistance of a switch and CS . The relatively small values of these components result in a typical full power input bandwidth of 250MHz for the converter. As illustrated in the functional block diagram, eight identical pipeline subconverter stages, each containing a two-bit flash converter and a two-bit multiplying digital-to-analog converter, follow the S/H circuit with the ninth stage being a two bit flash converter. Each converter stage in the pipeline will be sampling in one phase and amplifying in the other clock phase. Each individual subconverter clock signal is offset by 180 degrees from the previous stage clock signal resulting in alternate stages in the pipeline performing the same operation. The output of each of the eight identical two-bit subconverter stages is a two-bit digital word containing a supplementary bit to be used by the digital error correction logic. The output of each subconverter stage is input to a digital delay line which is controlled by the internal sampling clock. The function of the digital delay line is to time align the digital outputs of the eight identical two-bit subconverter stages with the corresponding output of the ninth stage flash converter before applying the eighteen bit result to the digital error correction logic. The digital error correction logic uses the supplementary bits to correct any error that may exist before generating the final ten bit digital data output of the converter. Because of the pipeline nature of this converter, the digital data representing an analog input sample is output to the digital data bus on the 7th cycle of the clock after the analog sample is taken. This time delay is specified as the data latency. After the data latency time, the digital data representing each succeeding analog sample is output during the following clock cycle. The digital output data is synchronized to the external sampling clock by a double 3-14 buffered latching technique. The digital output data is available in two’s complement or offset binary format depending on the state of the Data Format Select (DFS) control input. Internal Reference Voltage Output, VREFOUT The HI5767 is equipped with an internal reference voltage generator, therefore, no external reference voltage is required. VREFOUT must be connected to VREFIN when using the internal reference voltage. An internal band-gap reference voltage followed by an amplifier/buffer generates the precision +2.5V reference voltage used by the converter. A 4:1 array of substrate PNPs generates the “delta-VBE” and a two-stage op amp closes the loop to create an internal +1.25V band-gap reference voltage. This voltage is then amplified by a wideband uncompensated operational amplifier connected in a gain-of-two configuration. An external, user-supplied, 0.1µF capacitor connected from the VREFOUT output pin to analog ground is used to set the dominant pole and to maintain the stability of the operational amplifier. Reference Voltage Input, VREFIN The HI5767 is designed to accept a +2.5V reference voltage source at the VREF IN input pin. Typical operation of the converter requires VREFIN to be set at +2.5V. The HI5767 is tested with VREFIN connected to VREFOUT yielding a fully differential analog input voltage range of ±0.5V. The user does have the option of supplying an external +2.5V reference voltage. As a result of the high input impedance presented at the VREFIN input pin, 2.5kΩ typically, the external reference voltage being used is only required to source 1mA of reference input current. In the situation where an external reference voltage will be used an external 0.1µF capacitor must be connected from the VREFOUT output pin to analog ground in order to maintain the stability of the internal operational amplifier. In order to minimize overall converter noise it is recommended that adequate high frequency decoupling be provided at the reference voltage input pin, VREFIN . φ1 VIN + φ1 φ1 φ1 CS φ2 VIN - CH VOUT + + VOUT - CS φ1 CH φ1 FIGURE 10. ANALOG INPUT SAMPLE-AND-HOLD Application Note 9762 HI5767 Functional Block Diagram VDC CLOCK BIAS CLK VINVREFOUT VIN+ REFERENCE VREFIN S/H STAGE 1 DFS 2-BIT FLASH 2-BIT DAC OE + ∑ DVCC2 X2 D9 (MSB) D8 D7 D6 DIGITAL DELAY AND DIGITAL ERROR CORRECTION STAGE 8 D5 D4 D3 2-BIT FLASH 2-BIT DAC D2 D1 + ∑ D0 (LSB) - X2 DGND2 STAGE 9 2-BIT FLASH AVCC 3-15 AGND DVCC1 DGND1 Application Note 9762 Appendix E Pin Descriptions PIN NO. NAME DESCRIPTION 1 DVCC1 Digital Supply (+5.0V) 2 DGND1 Digital Ground 3 DVCC1 Digital Supply (+5.0V) 4 DGND1 Digital Ground 5 AVCC Analog Supply (+5.0V) 6 AGND Analog Ground 7 VREFIN +2.5V Reference Voltage Input 8 VREFOUT 9 VIN+ Positive Analog Input 10 VIN- Negative Analog Input 11 VDC DC Bias Voltage Output 12 AGND Analog Ground 13 AVCC Analog Supply (+5.0V) 14 OE Digital Output Enable Control Input 15 DFS Data Format Select Input 16 D9 Data Bit 9 Output (MSB) 17 D8 Data Bit 8 Output 18 D7 Data Bit 7 Output 19 D6 Data Bit 6 Output 20 D5 Data Bit 5 Output 21 DGND2 22 CLK 23 DVCC2 24 D4 Data Bit 4 Output 25 D3 Data Bit 3 Output 26 D2 Data Bit 2 Output 27 D1 Data Bit 1 Output 28 D0 Data Bit 0 Output (LSB) +2.5V Reference Voltage Output Digital Ground Sample Clock Input Digital Output Supply (+3.0V or +5.0V) All Intersil semiconductor products are manufactured, assembled and tested under ISO9000 quality systems certification. Intersil semiconductor products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see web site www.intersil.com 3-16