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Explain Instrumentation amplifier using 3 Op-Amp.
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  • Following diagram shows the instrumentation amplifier using 3 Op-Amp

    enter image description here

  • Instrumentation amplifier uses cross coupled difference amplifiers.

  • A1 and A2 are non-inverting amplifiers with their inverting terminal connected to $R_g$.

  • The input impedance of all the Op-Amps used is assumed to be infinite, therefore their input current is zero.

  • Thus current flowing through the resistors $R_1, R_g$ and $R_3$ is same.

  • The output voltage is given by

    $V_0 = A_V x (V_1-V_2)$

  • Where Av is the overall gain which is given by

    $AV = [1+2R_1/R_g]$ x $R_4/R_3$

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