• The first installment of this series introduced the boundary plot, an often-misunderstood plot found in instrumentation amplifier (IA) datasheets. • It also discussed various IA topologies: traditional three operational amplifier (op amp), two op amp, two op amp with a gain stage, current mirror, current feedback with super-beta transistors, and indirect current feedback. • Part 1 also included derivations of the internal node equations and transfer function of a traditional three-op-amp IA. • The second installment will introduce the input common-mode and output swing limitations of op amps, which are the fundamental building blocks of IAs. • Modifying the internal node equations from Part 1 yields equations that represent each op amp’s input common-mode and output swing limitation at the output of the IA as a function of the device’s input common-mode voltage. • The article will also examine a generic boundary plot in detail and compare it to plots from device datasheets to corroborate the theory.
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