There are two types of differentiator amplifiers: passive ones using only RC networks and active ones using transistors and op-amps. Active differentiators have higher output voltages and lower output resistance than passive ones. A differentiator amplifier outputs a voltage proportional to the rate of change of its input voltage. It acts as a high-pass filter, attenuating low frequencies and passing high frequencies. Differentiators are used in signal processing and instrumentation to monitor rate of change.