Sample-and-hold amplifier holds the difference of two inputs

摘要

You can fulfill a requirement for sampling the difference of two signals in two classic ways. You can subtract the two input signals with an instrumentation amplifier whose output connects to an input of a classic sample-and-hold amplifier. Despite the positive feature of needing no external resistors for a gain-of-one differencing instrumentation amplifier, this approach suffers from high relative output distortion when the inputs are of the same polarity and close in magnitude. In such a case, the difference of two input signals is close to OV, and the amplifier is therefore more vulnerable to residual dynamic imperfections of the sample-and-hold amp. The other approach is to separately sample the two input voltages in two sample-and-hold amps and subtract the outputs ofrnthese amps in an instrumentation amp. Here, the relative error of output signalrnwith similar input waveforms is lower than in the first approach.