The peak-to-peak monitor in Fig 1 uses three identical transistors and three identical resistors rather than a handful of op amps and their associated components. The circuit measures voltages up to ±2V p-p.
The peak-to-peak monitor in Fig 1 uses three identical transistors and three identical resistors rather than a handful of op amps and their associated components. The circuit measures voltages up to ±2V p-p.
For positive inputs, voltage follower Q1drives the output directly. The positive input also drives Q2 on, via R1. Consequently, Q2 holds Q3 off. For negative inputs, inverting amplifier Q2(gain of 1) drives voltage-follower Q3. The negative signal at Q1's base turns Q1 off. Choose capacitor C2 to give the desired decay time in parallel with the load. The load should be a 100-µA, 20-k Ohm meter or its equivalent.
The quiescent dc biases all lie conveniently at one VBE--about 0.6V--neatly temperature-compensated. The residual no-signal output is of no consequence; calibration always targets the peak levels that occur at the accurate end of the circuit's scale.
Some caveats: The VBER ratings of the transistors limit the peak voltages. The load on the driving circuit is mildly nonlinear and partially reactive, but the high gains of the 2N5089 transistors minimize the effect. If you must use an IC, try an transistor array. (DI #1630)