differentiator

In electronics, a differentiator is a circuit that outputs a signal approximately proportional to the rate of change (i.e. the derivative with respect to time) of its input signal. Because the derivative of a sinusoid is another sinusoid whose amplitude is multiplied by its frequency, a true differentiator that works across all frequencies can't be realized (as its gain would have to increase indefinitely as frequency increase). Real circuits such as a 1-order high-pass filter are able to approximate differentiation at lower frequencies by limiting the gain above its cutoff frequency. An active differentiator includes an amplifier, while a passive differentiator is made only of resistors, capacitors and inductors.

==Passive differentiator== The four-terminal 1-order passive high-pass filter circuits depicted in figure, consisting of a resistor and a capacitor, or alternatively a resistor and an inductor, approximate differentiation at frequencies well-below each filter's cutoff frequency.