SHC615

SHC615 BURR-BROWN | Alldatasheet

Document overview

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Technical content

©1994 Burr-Brown Corporation PDS-1214C Printed in the U.S.A. May, 1995 Wide-Bandwidth, DC RESTORATION CIRCUIT

APPLICATIONS

l BROADCAST/HDTV EQUIPMENT l TELECOMMUNICATIONS EQUIPMENT l HIGH-SPEED DATA ACQUISITION l CAD MONITORS/CCD IMAGE PROCESSING l NANO SECOND PULSE INTEGRATOR/ PEAK DETECTORS l PULSE CODE MODULATOR/ DEMODULATOR l COMPLETE VIDEO DC LEVEL RESTORATION l SAMPLE/HOLD AMPLIFIER optimized for low input bias current. The sampling comparator has two identical high-impedance inputs and a current source output optimized for low output bias current and offset voltage; it can be controlled by a TTL-compatible switching stage within a few nanoseconds. The transconductance of the OTA and sampling comparator can be adjusted by an external resistor, allowing bandwidth, quiescent current, and gain tradeoffs to be optimized. The SHC615 is available in SO-14 surface mount and 14-pin plastic DIPs, and is specified over the ex- tended temperature range of –40°C to +85°C.

FEATURES

l PROPAGATION DELAY: 2.2ns l BANDWIDTH: OTA: 750MHz Comparator: 280MHz l LOW INPUT BIAS CURRENT: –0.3 µA l SAMPLE/HOLD SWITCHING TRANSIENTS: +1/–7mV l SAMPLE/HOLD FEEDTHROUGH REJECTION: 100dB l CHARGE INJECTION: 40fC l HOLD COMMAND DELAY TIME: 3.8ns l TTL/CMOS HOLD CONTROL

DESCRIPTION

The SHC615 is a complete subsystem for very fast and precise DC restoration, offset clamping, and low frequency hum suppression of wideband amplifiers or buffers. Designed to stabilize the performance of video signals, it can also be used as a sample/hold amplifier, high-speed integrator, or peak detector for nanosecond pulses. A wideband Operational Transconductance Amplifier (OTA) with a high-im- pedance cascode current source output and fast sam- pling comparator set a new standard for high-speed applications. Both can be used as stand-alone circuits or combined to form a more complex signal process- ing stage. The self-biased, bipolar OTA can be viewed as an ideal voltage-controlled current source and is Switching Stage Biasing SHC615 ∞SOTA OTA 94 3 13 5 +V CC –VCC IQ Adjust Collector (IOUT ) Emitter C HOLD BaseGround Hold Control S/H In+ S/H In– Sampling Comparator (SC) SHC615 SHC615 SHC615 International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111 Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132

SHC615AP, AU PARAMETER CONDITIONS MIN TYP MAX UNITS OTA OFFSET VOLTAGE, V E at VB = 0 Initial 8 ±40 mV vs Temperature 40 µV/°C vs Supply (tracking) V CC = ±4.5V to ±5.5V 50 55 dB B-INPUT BIAS CURRENT Initial –0.3 ±0.9 µA vs Temperature 1 nA/ °C C-OUTPUT BIAS CURRENT, I C at VB = 0 Initial –200 –77 +100 µA B-INPUT IMPEDANCE 4.4 M Ω INPUT NOISE Voltage Noise Density, B-to-E f OUT = 100kHz to 100MHz 2.2 nV/ √Hz Voltage Noise Density, B-to-C f OUT = 100kHz to 100MHz 4.5 nV/ √Hz INPUT VOLTAGE RANGE ±3.4 V OUTPUT Output Voltage Compliance ±3.2 V C-Current Output ±18 ±20 mA E-Current Output ±18 ±20 mA C-Output Impedance 0.5 M Ω E-Output Impedance 12 Ω Open-Loop Gain 96 dB TRANSCONDUCTANCE Small Signal, <200mV 70 mA/V The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. DC SPECIFICATIONS At VCC = ±5V, RLOAD = 100Ω , RQ = 300Ω , RIN = 150Ω and TA = +25°C, unless otherwise specified.

DC SPECIFICATIONS (CONT) At VCC = ±5V, RLOAD = 1kΩ , RQ = 300Ω , and TA = +25°C, unless otherwise specified. SHC615AP, AU PARAMETER CONDITIONS MIN TYP MAX UNITS COMPARATOR INPUT BIAS CURRENT Initial 1.0 ±5 µA vs Temperature –2.3 nA/ °C C-OUTPUT BIAS CURRENT Initial ±10 ±50 µA vs Temperature ±13 nA/ °C INPUT IMPEDANCE Input Impedance 0.2 M Ω INPUT NOISE Voltage Noise Density f OUT = 100kHz to 100MHz 5 nV/ √Hz INPUT VOLTAGE RANGE Input Voltage Range ±3.0 V Common-Mode Input Range ±3.2 V OUTPUT Output Voltage Compliance ±3.5 V C-Current Output ±2.5 ±3.2 mA C-Output Impedance 620 || 2 k Ω || pF Open-Loop Gain 83 dB TRANSCONDUCTANCE Transconductance 22 mA/V HOLD CONTROL Logic 1 Voltage +2 +V CC +0.6 V Logic 0 Voltage 0 0.8 V Logic 1 Current V Hold Control = 5.0V 1 µA Logic 0 Current V Hold Control = 0.8V 0.05 µA TRANSFER CHARACTERISTICS Charge Injection Track-To-Hold 40 fC Feedthrough Rejection Hold Mode –100 dB COMPLETE SHC615 POWER SUPPLY Rated Voltage ±5V Derated Performance ±4.5 ±5.5 V Quiescent Current R Q = 300Ω± 12 ±15 ±18 mA Quiescent Current Range Programmable (Useful Range) ±3 to ±36 mA TEMPERATURE RANGE Operating –40 +85 °C Storage –40 +125 °C

At VCC = ±5V, RLOAD = 100Ω , RSOURCE = 50Ω, RQ = 300Ω , and TA = +25°C, unless otherwise specified. SHC615AP, AU PARAMETER CONDITIONS MIN TYP MAX UNITS FREQUENCY DOMAIN OTA LARGE-SIGNAL BANDWIDTH VOUT = 5.0Vp-p 430 MHz (–3dB), (B-to-E) V OUT = 2.8Vp-p 540 MHz VOUT = 1.4Vp-p 620 MHz SMALL-SIGNAL BANDWIDTH B-TO-E VOUT = 0.2Vp-p 520 MHz DIFFERENTIAL GAIN (B-TO-E) f = 4.43MHz, VOUT = 0.7Vp-p, RL = 150Ω 1.8 % R L = 500Ω 0.1 % DIFFERENTIAL PHASE f = 4.43MHz, VOUT = 0.7Vp-p, RL = 150Ω 0.07 ° (B-to-E) R L = 500Ω 0.01 ° HARMONIC DISTORTION (B-TO-E) f = 30MHz, VOUT = 1.4Vp-p Second Harmonic –50 dBc Third Harmonic –46 dBc LARGE SIGNAL BANDWIDTH (–3dB), (B-to-C) V OUT = 5.0Vp-p 250 MHz VOUT = 2.8Vp-p 580 MHz VOUT = 1.4Vp-p 750 MHz SMALL SIGNAL BANDWIDTH B-to-C V OUT = 0.2Vp-p 680 MHz COMPARATOR Sample Mode BANDWIDTH IOUT = 4mAp-p 240 MHz (–3dB) I OUT = 2mAp-p 270 MHz IOUT = 1mAp-p 280 MHz TIME DOMAIN OTA RISE TIME 2Vp-p Step, 10% to 90% B-to-E 1.1 ns B-to-C 1.2 ns SLEW RATE 2Vp-p,B-to-E 1800 V/ µs B-to-C 1700 V/ µs 5Vp-p,B-to-E 3300 V/ µs B-to-C 3000 V/ µs COMPARATOR RISE TIME 10% to 90%, RL = 50Ω, IOUT = ±2mA (Sample Mode) C LOAD = 1pF 2.5 ns SLEW RATE 10% to 90%, RL = 50Ω, IOUT = ±2mA (Sample Mode) C LOAD = 1pF 0.95 mA/ns DYNAMIC CHARACTERISTICS Propagation Delay Time t PDH , VOD = 200mV 2.2 ns Propagation Delay Time t PDL , VOD = 200mV 2.15 ns Delay Time Sample-to-Hold 3.8 ns Hold-to-Sample 3.0 ns

Top View DIP, SO-14 BLOCK DIAGRAM IQ Adjust Emitter, E Base, B C HOLD –VCC NC Hold Control NC +VCC IOUT , Collector, C S/H In– S/H In+ Ground NC

• 14 SHC615 NOTE: (1) Inputs are internally diode-clamped to ±VCC . ABSOLUTE MAXIMUM RATINGS ELECTROSTATIC DISCHARGE SENSITIVITY Any integrated circuit can be damaged by ESD. Burr-Brown recommends that all integrated circuits be handled with ap- propriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet published speci- fications. PACKAGE DRAWING TEMPERATURE PRODUCT PACKAGE NUMBER (1) RANGE SHC615AP Plastic 14-Pin DIP 010 –40 °C to +85°C SHC615AU SO 14-Lead Surface-Mount 235 –40 °C to +85°C NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. PACKAGE/ORDERING INFORMATION Switching Stage Biasing SHC615 ∞SOTA OTA 94 3 13 5 +VCC –VCC IQ Adjust Collector (IOUT ) Emitter C HOLD BaseGround Hold Control S/H In+ S/H In– Sampling Comparator (SC)

TYPICAL PERFORMANCE CURVES At RQ = 300Ω , TA = +25°C, VCC = ±5V, unless otherwise noted. OPERATIONAL TRANSCONDUCTANCE AMPLIFIER SHC615 TOTAL QUIESCENT CURRENT vs R Q 100 10 100 1000 10000 R Q (Ω ) Total Quiescent Current, IQ (mA) TOTAL QUIESCENT CURRENT vs TEMPERATURE 1.50 1.40 1.30 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 –25 0 25 50 75 100 Temperature (C°) Total Quiescent Current, IQ (Normalized) OTA B-INPUT BIAS CURRENT vs TEMPERATURE 0.0 –0.1 –0.2 –0.3 –0.4 –0.5 –0.6 –0.7 –0.8 –0.9 –1.0 –25 0 25 50 75 100 Temperature (C°) OTA-B Input Bias Current (µA) OTA-B INPUT OFFSET VOLTAGE vs TEMPERATURE –25 0 25 50 75 100 Temperature (C°) OTA-B Input Offset Voltage (mV) R E = 100Ω OTA-B INPUT RESISTANCE vs TOTAL QUIESCENT CURRENT 5 1 01 52 02 53 03 54 0 Total Quiescent Current, I Q (mA) OTA-B Input Resistance (MΩ ) OTA-E OUTPUT RESISTANCE vs TOTAL QUIESCENT CURRENT 4 9 14 19 24 29 34 39 Total Quiescent Current, I Q (mA) OTA-E Output Resistance (Ω )

TYPICAL PERFORMANCE CURVES (CONT) At RQ = 300Ω, TA = +25°C, VCC = ±5V, unless otherwise noted. OTA-C OUTPUT RESISTANCE vs TOTAL QUIESCENT CURRENT 1.8 1.6 1.4 1.2 0.8 0.6 0.4 0.2 5 1 01 52 02 53 03 54 0 Total Quiescent Current, I Q (mA) OTA-C Output Resistance (MΩ ) OTA-C OUTPUT BIAS CURRENT vs TEMPERATURE –60 –65 –70 –75 –80 –85 –90 –95 –100 Temperature (°C) –40 –20 0 20 40 60 80 100 OTA-C Output Bias Current (µA) OTA TRANSFER CHARACTERISTICS vs INPUT VOLTAGE –10 –15 –20 –25 OTA-B Input Voltage (V) OTA-C Output Current (mA) IQ = ±14mA IQ = ±25mA IQ = ±5mAVIN 150Ω VOUT 100Ω R C 100Ω R E OTA OTA TRANSFER CHARACTERISTIC vs INPUT VOLTAGE –10 –15 –20 –25 OTA-B Input Voltage (V) OTA-C Output Current (mA) IQ = ±25mA IQ = ±14mA IQ = ±5mA VIN 150Ω VOUT 100Ω R C OTA OTA TRANSCONDUCTANCE vs TOTAL QUIESCENT CURRENT 100 Total Quiescent Current, I Q (mA) Transconductance (mA/V) Small Signal (<200mV) OTA-TRANSCONDUCTANCE vs FREQUENCY 100 1.0 10k 100k 1M 10M 100M 1G Frequency (Hz) Transconductance (mA/V) IQ = ±25mA IQ = ±5mA IQ = ±14mA Large Signal (>200mV)

OTA-E VOLTAGE NOISE SPECTRAL DENSITY 100 1k 10k 100k Frequency (Hz) TYPICAL PERFORMANCE CURVES (CONT) At RQ = 300Ω, TA = +25°C, VCC = ±5V, unless otherwise noted. OTA-C Voltage Noise Density (nV/√Hz) OTA-E Voltage Noise Density (nV/√Hz) 2.2nV/√Hz OTA-E FREQUENCY RESPONSE –10 –20 –30 300k 1M 10M 100M 1G Frequency (Hz) Gain (dB) 0.6Vp-p 0.2Vp-p 150Ω VOUT 50Ω 3VIN 2.8Vp-p 1.4Vp-p 5Vp-p OTA OTA-E SMALL SIGNAL PULSE RESPONSE 150 100 –50 –100 –150 0 2 04 06 08 0 1 0 0 Time (ns) OTA-E Output Voltage (mV) R IN = 150Ω , RL = 100Ω , VIN = 200mVp-p, tRISE = tFALL = 1.5ns (Generator) OTA-E LARGE SIGNAL PULSE RESPONSE 0 2 04 06 08 0 1 0 0 Time (ns) OTA-E Output Voltage (V) R IN = 150Ω , RL = 100Ω , VIN = 4Vp-p, tRISE = tFALL = 1.5ns (Generator) OTA-C VOLTAGE NOISE SPECTRAL DENSITY 100 1k 10k 100k Frequency (Hz) 4.5nV/√Hz –10 –20 –30 –40 OTA-C FREQUENCY RESPONSE 300k 1M 10M 100M 1G Frequency (Hz) Gain (dB) 150Ω VOUT 50Ω 100Ω 100Ω 3VIN 5Vp-p 2.8Vp-p 1.4Vp-p 0.6Vp-p 0.2Vp-p OTA

TYPICAL PERFORMANCE CURVES (CONT) At RQ = 300Ω, TA = +25°C, VCC = ±5V, unless otherwise noted. SAMPLING COMPARATOR OTA-C SMALL SIGNAL PULSE RESPONSE 150 100 –50 –100 –150 0 2 04 06 08 0 1 0 0 Time (ns) OTA-C Output Voltage (mV) R IN = 150Ω , RE = 100Ω , RC = 100Ω , VIN = 200mVp-p, tRISE = tFALL = 1.5ns (Generator) OTA-C LARGE SIGNAL PULSE RESPONSE 0 2 04 06 08 0 1 0 0 Time (ns) OTA-C Output Voltage (V) R IN = 150Ω , RE = 100Ω , RC = 100Ω , VIN = 4Vp-p, tRISE = tFALL = 1.5ns (Generator) OTA-E HARMONIC DISTORTION vs FREQUENCY –45 –46 –47 –48 –49 –50 –51 –52 –53 1M 10M 100M Frequency (Hz) OTA-E Harmonic Distortion (dBc) R E = 100Ω OTA-C HARMONIC DISTORTION vs FREQUENCY –10 –15 –20 –25 –30 –35 –40 –45 –50 1M 10M 100M VOUT = 1.4Vp R E = RC = 100Ω Frequency (Hz) OTA-C Harmonic Distortion (dBc) INPUT BIAS CURRENT vs TEMPERATURE 1.4 1.2 1.0 0.8 0.6 0.4 0.2 –40 –20 Temperature (C°) Input Bias Current (µA) S/H In+ S/H In– 0 2 04 06 08 0 100 OUTPUT BIAS CURRENT vs TEMPERATURE –10 –40 Temperature (°C) Output Bias Current (µA) –20 0 20 40 60 80 100

TYPICAL PERFORMANCE CURVES (CONT) At RQ = 300Ω, TA = +25°C, VCC = ±5V, unless otherwise noted. INPUT RESISTANCE vs TOTAL QUIESCENT CURRENT 0.7 0.6 0.5 0.4 0.3 0.2 0.1 5 1 01 52 02 53 03 54 0 Total Quiescent Current, I Q (mA) Input Resistance (MΩ ) TRANSCONDUCTANCE vs TOTAL QUIESCENT CURRENT 0 5 10 15 20 25 Total Quiescent Current, I Q (mA) Transconductance (mA/V) TRANSFER CHARACTERISTICS Input Voltage (V) Comparator Output Current (mA) IQ = ±25mA IQ = ±14mA IQ = ±5mA TRANSCONDUCTANCE vs INPUT VOLTAGE –10 Input Voltage (V) Comparator Transconductance (mA/V) IQ = ±25mA IQ = ±14mA IQ = ±5mA PROPAGATION DELAY vs TOTAL QUIESCENT CURRENT 3.5 2.5 1.5 8 1 31 82 12 83 33 8 Total Quiescent Current, IQ (mA) Delay (ns) Pos Neg COMMON-MODE REJECTION vs FREQUENCY –20 –40 –60 –80 –100 Frequency (Hz) 1M300k 10M 100M 1G Common-Mode Rejection (dB)

TYPICAL PERFORMANCE CURVES (CONT) At RQ = 300Ω, TA = +25°C, VCC = ±5V, unless otherwise noted. PROPAGATION DELAY vs OVERDRIVE 2.5 1.5 0.5 0 200 400 600 800 100 1200 Δ Input Voltage (mV) VOD VOD VOD GND Pos Neg Propogation Delay (ns) 100Ω 100Ω 4 11 SC PROPAGATION DELAY TIME vs TEMPERATURE 2.8 2.6 2.4 2.2 1.8 1.6 –40 –20 0 20 40 60 80 100 120 Temperature (°C) Propagation Delay (ns) Pos Neg PROPAGATION DELAY vs LOAD CAPACITANCE 0 100 200 300 400 500 600 700 800 900 1000 Capacitive Load, C L (pF) Propagation Delay (ns) Pos Neg 11 SC C LOAD PROPAGATION DELAY vs SLEW RATE 3.5 2.5 1.5 (0) 500 (2) 250 (4) 160 (6) 120 (8) (10) (12) (14) (16) (18) (20) Slew Rate (V/µs) (Rise Time (ns)) Propagation Delay (ns) Pos Neg VIN = 1.2Vpp VREF –0.6V +0.6V VOD = 1.2Vp-p COMPARATOR RESPONSE TO A 2ns ANALOG INPUT PULSE 150 100 –50 –100 –150 Output Voltage (mV) Time (ns) 0 2 04 0 6 08 0 1 0 0 IOUT = 4mAp-p R L = 50Ω COMPARATOR RESPONSE TO A 10ns ANALOG INPUT PULSE 150 100 –50 –100 –150 Output Voltage (mV) Time (ns) 0 2 04 0 6 08 0 1 0 0 IOUT = 4mAp-p R L = 50Ω

TYPICAL PERFORMANCE CURVES (CONT) At RQ = 300Ω, TA = +25°C, VCC = ±5V, unless otherwise noted. 100Ω 150Ω 200Ω 200Ω 50Ω TTL 50Ω 100Ω TTL Comparator CD74HCT 711 SWITCHING TRANSIENTS TEST CIRCUITS SC Switching Transients (mV) –10 –15 Time (ns) 0 20 40 60 80 100 On-Off Off-On SWITCHING TRANSIENTS FEEDTHROUGH REJECTION vs FREQUENCY (Off-Isolation) –20 –40 –60 –80 –100 –120 300k 1M 10M 100M 1G Frequency (Hz) Feedthrough Rejection (dB) BANDWIDTH vs OUTPUT CURRENT SWING –10 –20 –30 –40 100k 1M 10M 100M 1G Frequency (Hz) Gain (dB) ±2mA ±1mA ±0.5mA 100Ω 50Ω 100Ω 50Ω 4VIN SC VOUT SLEW RATE vs TOTAL QUIESCENT CURRENT 3.5 2.5 1.5 0.5 0 5 10 15 20 25 30 35 40 Total Quiescent Current, IQ (mA) Slew Rate (mA/ns) Pos Neg HOLD COMMAND DELAY TIME 100 –100 0 1 02 03 0 4 05 0 Time (ns) Output Voltage (mV) Hold Command (V) IOUT = 2mA IOUT = –2mA

The SHC615, which contains a wideband Operational Transconductance Amplifier and a fast sampling compara- tor, represents a complete subsystem for very fast and precise DC restoration, offset clamping and correction to GND or to an adjustable reference voltage, and low fre- quency hum suppression of wideband operational or buffer amplifiers. Although the IC was designed to improve or stabilize the performance of complex, wideband video signals, it can also be used as a sample and hold amplifier, high-speed integra- tor, peak detector for nanosecond pulses, or demodulator or modulator for pulse code transmission systems. A wideband Operational Transconductance Amplifier (OTA) with a high- impedance cascode current source output and a fast and precise sampling comparator set a new standard for high- speed sampling applications. Both can be used as stand-alone circuits or combined to create more complex signal processing stages like sample and hold amplifiers. The SHC615 simplifies the design of input amplifiers with high hum suppression, clamping or DC-restoration stages in professional broadcast equipment, high-resolution CAD monitors and information terminals, signal processing stages for the energy and peak value of small and fast nanoseconds pulses, and eases the design of high-speed data acquisition systems behind a CCD sensor or in front of an analog-to-digital converter. An external resistor, RQ , allows the user to set the quiescent current. RQ is connected from Pin 1 (IQ adjust) to –VCC . It determines the operating currents of both the OTA and comparator sections and controls the bandwidth and AC behavior as well as the transconductance of both sections. Besides the quiescent current setting feature, the Propor- tional-to-Absolute-Temperature (PTAT) supply increases the quiescent current vs temperature and keeps it constant over a wide range of input voltages. This variation holds the transconductance gm of the OTA and comparator relatively constant vs temperature. The circuit parameters listed in the specification table are measured with RQ set to 300Ω , giving a nominal quiescent current at ±15mA. The circuit can be totally switched-off with a current flowing into Pin 1. OPERATIONAL TRANSCONDUCTANCE AMPLIFIER (OTA) SECTION AND OVERVIEW The symbol for the OTA section is similar to that of a bipolar transistor, and the self-based OTA can be viewed as a quasi-ideal transistor or as a voltage-controlled current source. Application circuits for the OTA look and operate much like transistor circuits—the bipolar transistor, also, is a voltage-controlled current source. Like a transistor, it has three terminals: a high-impedance input (base) optimized for a low input bias current of 0.3µA, a low-impedance input/ output (emitter), and the high-impedance current output (collector). The OTA consists of a complementary buffer amplifier and a subsequent complementary current mirror. The buffer amplifier features a Darlington output stage and the current mirror has a cascoded output. The addition of this cascode circuitry increases the current source output resistance to 1M Ω and the open-loop gain to typically 96dB. Both fea- tures improve the OTAs linearity and drive capabilities. Any bipolar input voltage at the high impedance base has the same polarity and signal level at the low impedance buffer or emitter output. For the open-loop diagrams the emitter is connected to GND and then the collector current is deter- mined by the product voltage between base and emitter times the transconductance. In application circuits (Figure 2b.), a resistor RE between emitter and GND is used to set the OTA transfer characteristics. The following formulas describe the most important relationships. rE is the output impedance of the buffer amplifier (emitter) or the reciprocal of the OTA transconductance. Above ±5mA, collector cur- rent, IC , will be slightly less than indicated by the formula. The R E resistor may be bypassed by a relatively large capacitor to maintain high AC gain. The parallel combina- tion of RE and this large capacitor form a high pass filter enhancing the high frequency gain. Other cases may require a RC compensation network parallel to RE to optimize the high-frequency response. The full power bandwidth mea- sured at the emitter achieves 620MHz. The frequency re- sponse of the collector is directly related to the resistor’s value between collector and GND; it decreases with increas- ing resistor values, because it forms a low-pass network with the OTA C-output capacitance. Figure 1 shows a simplified block and circuit diagram of the SHC615 OTA. Both the emitter and the collector outputs offer a drive capability of ±20mA for driving low impedance lines or inputs. Connecting the collector to the emitter in a direct-feedback buffer configuration increases the drive capability to ±40mA. The emitter output is not current-limited or protected. Momentary shorts to GND should be avoided, but are unlikely to cause permanent damage. While the OTA’s function and labeling looks similar to that of transistors, it offers essential distinctive differences and improvements: 1) The collector current flows out of the C terminal for a positive B-to-E input voltage and into it for negative voltages; 2) A common emitter amplifier operates in non-inverting mode while the common base operates in inverting mode; 3) The OTA is far more linear than a bipolar transistor; 4) The transconductance can be adjusted with an external resistor; 5) Due to the PTAT biasing characteristic the quiescent current increases as shown in the typical performance curve vs temperature and keeps the AC performance constant; 6) The OTA is self-biased and bipolar; and, 7) The output current is zero for zero differential input voltages. AC inputs centered at zero produce an output current centered at zero. IC = V IN rE + R E R E = V IN IC ±r E

• Bypass power supplies very close to the device pins. Use tantalum chip capacitors (approximately 2.2µF); parallel 470pF and/or 10nF ceramic chip capacitors may be added if desired. Surface mount types are recommended because of their low lead inductance. Supply bypassing is extremely critical at high frequen- cies and when driving high current loads.
• PC board traces for power lines should be wide to reduce impedance. If the high speed TTL-hold command signal goes negative due to reflections for AC-coupling, the hold control input must be protected by an external reverse bias diode to ground as shown in Figure 6. CIRCUIT LAYOUT The high-frequency performance of the SHC615 can be greatly affected by the physical layout of the printed circuit board. The following tips are offered as suggestions, not as absolute requirements. Oscillations, ringing, poor bandwidth, poor settling, and peaking are all typical problems that

FIGURE 5. a) Simplified Block Diagram; and, b) Circuit Diagram of the Sampling Comparator which Includes the Sampling Operational Transconductance Amplifier (SOTA) and the Switching Stage.

• Make short, low-inductance traces. The entire physical circuit should be as small as possible.
• Use a low-impedance ground plane on the component side to ensure that a low-impedance ground is available through- out the layout.
• Do not extend the ground plane under high-impedance nodes sensitive to stray capacitances such as the amplifier’s input terminals.
• Sockets are not recommended since they add significant inductance and parasitic capacitance. If sockets are re- quired, use zero-profile sockets.
• Use low-inductance, surface-mount components. Surface- mount components offer the best AC performance.
• A resistor of 100 to 250Ω in series with the high-imped- ance inputs is recommended to reduce peaking.
• Plug-in prototype boards and wire-wrap boards will not function well. A clean layout using RF techniques is essential—there are no shortcuts.
• Terminate transmission line loads. Unterminated lines, such as box cables, can appear to the amplifier to be a capacitive or inductive load. By terminating a transmission line with its characteristic impedance, the amplifier’s load then appears purely resistive.
• Protect the hold control input with an external diode if necessary. NOTE: (1) ±VCC = ±6V absolute max.

FIGURE 6. Basic Connections