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<p>
The circuit on top uses an op-amp and a small capacitor to simulate a
much larger capacitor. It simulates the circuit on the bottom; the
resistor R2 is the same size as the resistor in the circuit being
simulated (R3), but the capacitor C1 is 100 times smaller than C2.
<p>
Current flows from the input source through R1 to the capacitor (C1).
Since R1 is 100 times larger than R2, there is 1/100th the current
through it into the capacitor. For a given input voltage, the rate of
change in voltage in C1 is the same as in C2, because C2 has 100 times the
capacitance to make up for 1/100th the current.
<p>
So the voltages across the two capacitors are the same, but the currents
are not. The op-amp causes the – input to be held at the same voltage
as the voltage across C1. This means R2 has the same voltage across it as
R3, and therefore the same current.
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<br>Generated Wed Dec 7 2016
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