Instrumentation Amplifier
Suppose you are measuring a very small signal (~mVs) from a thermocouple with an amplifier. There are three characteristics you would be interested in:
- The input impedance since a thermocouple cannot provide much current (limited power output).
- The gain for the potential difference measured on the thermocouple since this is the part that is related to the temperature. For this case a gain of 100-1000 would be desirable.
- The gain for a signal that exists on both wires of the thermocouple, since we are not really interested in this because it may be just noise, and the actual difference is what is important.
An instrumentation amplifier addresses these issues. If op-amps were ideal, this could be done with voltage followers and a differencing amplifier. This doesn’t work with real op-amps.