Instrumentation Amplifier – Comparing Three Opamp vs Single Opamp Implementations


I read in a book three opamp instrumentation amplifiers are better and they are more common, but why is it better than the single opamp instrumentation amplifier? It must be more expensive as they have two extra opamps.

Best Answer

First, many InAmps are integrated into one IC, also the three-opamp versions. Then the cost of the extra opamps isn't that high. Consider the extra cost of less than a mm^2 real estate against the total cost to create an IC.

Next, I've never seen a single-opamp inamp. There are two-opamp and three-opamp versions, and there's a reason why you can't make one with a single opamp: you need high impedance for both inputs, and that means neither can have feedback.

You probably mean a differential amplifier, like The Resistance comments below. Notice that the 2 input opamps are configured as non-inverting amplifiers, and that there's no feedback to the input pins, like you would have for an inverting amplifier. This way you get high-impedance amplifying buffer-amps before the actual differential amplifier.