The differentiator circuit is essentially a high-pass filter. It can generate a square wave from a triangle wave input and produce alternating-direction voltage spikes when a square wave is applied.

Why differentiator is a high-pass filter?

The High-pass RC circuit is also known as a differentiator. The name high pass is so called because the circuit blocks the low frequencies and allows high frequencies to pass through it. It is due to reason that reactance of the capacitor decreases with the increasing frequency.

Can the active high-pass filter act as differentiator?

High Pass Filter as Differentiator

This is same as for a differentiator. Hence the high pass filter is said to be behaved as a differentiator. If time constant of the RC HPF is very much smaller than time period of the input signal, then circuit behaves as a differentiator.