The circuit in Fig 1 combines a dual-matched op amp, IC1, with a video-difference amplifier, IC2, to form a high-frequency instrumentation amplifier. Table 1 shows the circuit’s performance for ±5V operation. You can configure the circuit for different gains and operate it using supplies ranging from ±4 to ±16.5V.
Judiciously distributing the circuit’s overall gain between IC1 and IC2 such that (for a particular configuration) the closed-loop bandwidths of both stages are equal yields a 290-MHz gain-bandwidth product. Preamplifier IC1’s referred-to-input (RTI) voltage noise and dc offset dominate IC2’s RTI voltage noise. Adding capacitor C1 causes peaking in IC2’s response, which counters IC1’s high-frequency rolloff. Determine the best value for C1 in your application by Spice simulation or breadboarding.
In this circuit, if IC1 has a gain of 5 or higher (A=(2RF/RG)+1), the circuit has an RTI voltage noise of 15 nV/ÖHz and an input voltage offset of 600 µV.(DI #1402)
| Table 1—Performance at ±5 | ||||||||
|---|---|---|---|---|---|---|---|---|
| AV | 3-dB bandwidth (MHz) | Slew rate (V/µsec) | Settling time to 0.1% (nsec) | CMRR (dB at 1 MHz) | VN at 10 kHz (nV/[ ]Hz) | IN at 10 kHz (pA/[ ]Hz) | VOS (mV) | IS (mA) |
| 10 | 14.2 | 200 | 80 | 64 | 15 | 1.5 | 0.6 | 27.5 |
| 50 | 5.8 | 60 | 200 | 64 | 15 | 1.5 | 0.6 | 27.5 |