This is a circuit for a simple circuit for removing an AC ripple from a DC voltage. The main component of the circuit is an operational amplifier configured as a simple amplifier in common-mode operation. This means that both the inverting and non-inverting inputs of the op-amp get the same input voltage, i.e., a DC voltage Vin with an AC ripple Vripple. The only difference is that the inverting input has an input capacitor that blocks the DC voltage. This is the figure of the circuit;
Since the op-amp amplifies just the difference between the voltages at its two inputs, it cancels out the AC ripple (which appears at both inputs). On the other hand, the op-amp amplifies the DC voltage Vin since this is only present at the non-inverting input. However, the op-amp is configured to have a DC voltage gain equal to 1, so the output of this circuit is just equal to Vin. Since the AC ripple can only be cancelled cleanly if both op-amp inputs have equal gains, the 10K potentiometer is used to compensate for any inherent differences between the inputs' gains.
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