Typical values of in amp CMR are from 70 to over 100 dB (at DC), with CMR usually improving at higher gains. This requires that in amps have very high common-mode rejection (CMR). In order to be effective, an in amp needs to be able to amplify microvolt-level signals, while simultaneously rejecting volts of CM signal at its inputs. This feature is especially useful in single-supply applications, where the output voltage is usually referenced to mid-supply (i.e., +2.5 V in the case of a + 5 V supply). In many applications, this pin is connected to circuit ground, but it can be connected to other voltages, as long as they lie within the rated compliance range of the in amp. The in amp develops an output voltage which is referenced to a pin usually designated REFERENCE or V REF. The generic instrumentation amplifier (in amp) An op amp is configured via a number of external components, while an in amp is configured either by one resistor, or by pin-selectable taps for its working gain.įigure 2-9. It can only be programmed for gain, and then over a specific range. In contrast to this, an in amp cannot be programmed to do just anything. Perhaps a good way to differentiate the two devices is to remember that an op amp can be programmed to do almost anything, by virtue of its feedback flexibility. It should be understood that an in amp is not just a special type op amp the function of the two devices is fundamentally different. People also often confuse in amps as to their function, calling them “op amps.” But the reverse is seldom (if ever) true. In many ways, it is better suited to its task than would be an op amp-even though, ironically, an in amp may actually comprise of a number of op amps within it. In contrast to this, an in amp is a more constrained device in terms of functioning, and also the allowable range(s) of operating gain. The final configuration and circuit function using an op amp is truly whatever the user makes of it. As already discussed, an op amp is a general-purpose gain block-user-configurable in myriad ways using external feedback components of R, C, and, (sometimes) L. Walt Kester, Walt Jung, in Op Amp Applications Handbook, 2005 Op Amp/In Amp Functionality DifferencesĪn in amp is unlike an op amp in a number of very important ways.
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