instrumentation, difference amp, and single op-amp

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

It seems to me common mode rejection is much better in a monolithic instrumentation amplifiers than it is in difference amps, or single op-amps. The amount of noise boils down in some cases to only amplifying the difference in the signals instead of what is common to the signals. Noise is usually what is common to both signals. Instrumentation amplifiers in some respects seem almost like differential signaling with a single ended output. I do understand that instrumentation amplifiers are not exactly differential signaling. I suspect instrumentation amplifiers have not been widely used in the music industry because of cost. In the past most In-Amps were built with three discrete op-amps, and before that with transistors. Extremely close resistor matching was a big problem in building 3 op amp IN-Amps. Monolithic chips with three op-amps inside have become popular. Resistors are lazier trimmed to be exact at the factory. Seems to me the IA have a great noise advantage over difference amps or common single op-amps.

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