ELEC 242 Lab

Experiment 5.2

Op-Amp Circuits

Equipment

Components

With a little imagination, and at the proper frequencies, the last two circuits of the previous experiment could be thought of as an integrator and a differentiator, respectively. This is not too surprising, since the voltage and current in a capacitor are the integral/derivative of each other. We can make this approximate behavior more exact, and extend it over a wider range of frequencies, by adding an op-amp to the circuit.

Part 1: Integrator

A true integrator is difficult to use in open loop mode, since if the input has a non-zero average value (DC offset) it will integrate the corresponding constant term until the output voltage reaches one of the supply voltages (plus or minus 15 V) and saturates. We can reduce this problem by building what is known as a leaky integrator where we place a large resistor across the capacitor to drain off the accumulated charge. This reduces the accuracy for low frequency signals, but can give acceptable performance for higher frequencies.


Step 1:

 Wire the following circuit. is a 1 megohm resistor to provide the "leak".


Step 2:

 Sketch the output for each of the following 1 kHz inputs: 10 V p-p square wave, 10 V p-p triangle wave, 10 V p-p sine wave. It may be necessary to adjust the DC OFFSET control on the function generator to center the output waveform.

Part 2: Differentiator



Step 1:

 Wire the following circuit. Since the derivative of a constant is zero, we don't need a "leak" for a differentiator.


Step 2:

 Sketch the output for each of the following 100 Hz inputs: 0.2 V p-p square wave, 10 V p-p triangle wave, 10 V p-p sine wave.