ECE 203 - Lecture 8 - Instrumentation Amplifiers I

This video is the first of three videos discussing the design of instrumentation amplifiers for biomedical applications. In this lecture we will first define some of the requirements in terms of input impedance, noise, gain, bandwidth, CMRR, and so on, and then discuss possible op-amp based options.

[anasshaydar]

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[tolgauye]

Thank you so much for this great course !

[ytubeleo]

At 40:00, I can't see any advantage in CMRR at all, compared to using the same gain of 80 dB (10, 000) with the single op amp difference amplifier design mentioned earlier. The improved CMRR just comes from using a gain of 10, 000 instead of 100. It appears to be nothing to do with using a fully-differential-mode amplifier before the difference amplifier.

The only benefit seems to be high input impedance (which is definitely a great feature) but that could be achieved with buffer amps. In fact, the three op amp design reduces the allowable Vcm common-mode voltage compared to the single op amp design (otherwise the output of the input amps will saturate due to gain in the first stage).

The only advantage I can find is the ability to set/adjust the gain with a single resistor. Or am I missing something here? Thanks!