Q. What is the principle of operation of an integrating circuit?

The RC integrator is typically a series RC circuit that uses the capacitor to develop its output. Since voltage cannot change instantly across a capacitor, because it takes time to charge, the output of an integrator lags the input voltage. When a sine wave voltage is applied to an integrator little or no distortion takes place. In other words, when a sine wave voltage is applied to the input a sine wave voltage develops across the integrator's output (the capacitor). The output is attenuated, however, and lags Va.

The input to our integrator is a square wave and it undergoes a great amount of distortion as it is processed by the RC integrator circuit . The first thing to go is the sharp corner of the square wave. 90-degree corners of a waveform represent very fast voltage transitions. Since the voltage across a capacitor cannot change instantly (because charging and discharging require time), and since an integrator uses a capacitor to develop its output, these transitions are lost on the integrator's output.The pulse portion of the wave is the time period in which the capacitor is forced to charge." idle" or "off" time is the time the capacitor is given to discharge.