The purpose of this lab is to become acquainted with the use of comparators and the use of comparators with hysteresis (Schmitt triggers) for waveform generation. We will use the LM319 dual-comparator integrated circuit. The LM319 contains two specially-designed, fast comparators in one dual-in-line package. The output of each comparator is high or low depending on whether the difference between the two inputs is greater than or less than zero. (An op-amp without feedback also behaves as a comparator, but is not suitable for high-speed operation because of slew rate limitations. How long would it take the output of a 741 Amplifier to switch between +10 and -10 volts?)

  1. Construct the following simple comparator circuit and investigate how the output and input waveforms are related as the reference level is varied.
  2. The comparator can be given hysteresis by providing some positive feedback, as below (section 12.4). (This circuit is called a Schmitt trigger, and is widely used in digital circuits to prevent multiple output transitions as a noisy input signal passes through the reference voltage.)
  3. The Schmitt trigger can be used to construct a relaxation oscillator as shown below. If these oscillators do not work, break the loop and input the expected signal. See if the signal progresses around the loop as expected.

  4. Voltage Controlled Oscillator. The Schmitt trigger can also be used with a current source to produce a sawtooth or triangle wave.

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