Operational Amplifier Applications Unit 2 – Integration and Differentiation
Exercise 2 – The Differentiator
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to determine the effects of an active
differentiator on an input waveform. You will verify your results with an oscilloscope.
DISCUSSION
- This is an active differentiator circuit. The op amp (U1) is the active component.
- The differentiating network is formed by R 2 and C 1.
- The op amp acts like an inverting amplifier.
- R 1 limits the high frequency gain of the circuit.
- The load resistor is R 3.
- When square wave inputs are applied, the differentiated output is inverted with respect to the
input. - Triangle input waveforms are differentiated into square waves.
- Low frequency sinusoidal input signals are differentiated into a 90° phase shifted sinusoidal
waveform. - The phase shift approaches 180° as the frequency increases to the breakpoint.
- Output signal amplitude increases as frequency increases. Therefore, for sinusoidal input
signals, the active differentiator tends to pass high frequencies. - The breakpoint frequency is the frequency at which the feedback capacitor’s reactance equals
the resistance (R 1 = XC1). - The active differentiator has two distinct operating regions, which can be seen by viewing the
gain versus frequency curve. - Frequencies below the breakpoint, differentiation occurs and gain increases with increasing
frequency. At and above the breakpoint frequency, the signal is passed with maximum gain. - For practical differentiators, choose a relatively high breakpoint frequency to make use of the
widest possible differentiator region.