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Instrumentation Amplifier




An instrumentation amplifier is a type of Differential Amplifier that has been specifically designed to have characteristics suitable for use in measurement and Test Equipment . These characteristics include very low DC offset, low Drift , low Noise , very high Open-loop Gain , very high Common-mode Rejection Ratio , and very high Input Impedance s. They are used where great Accuracy and Stability of the Circuit both short- and long-term are required.

The 3 Opamp version of the instrumentation amplifier is shown here. The gain for this circuit is calculated as follows:

:{V_\mathrm{out} \over V_\mathrm{in}} = -\left (1 + {2 R_1 \over R_\mathrm{gain}} ight ) {R_3 \over R_2}

There are also integrated devices available such as the
AD620 (approx $12) or AD624 (approx $35) from Analog Devices


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