Instrumentation Amplifiers

Notes

1. Common Mode Rejection Ratio specifies the ratio of the output voltage caused by a differential input voltage vs. a common mode input voltage.  Ideally infinite; 100dB = 100,000 the sensitivity to differential noise than common-mode noise.  This is the fundamental reason to use instrumentation amplifiers: to amplify small differential signals that ride upon large and possibly varying common-mode signals, especially when the source impedance of the signal is high encouraging capacitive coupling of 60Hz powerline and radiofrequency noise.
2. The output voltage swing is usually not rail-to-rail (i.e. cannot go entirely between the low and high chip supply voltages).  Vswing limit refers to how close the output voltages can approach the positive and negative voltage supply rails (e.g. an AD620 powered from 0 and 5V can have an output that varies from 1.2 to 3.8V).