Basic Op-amp Circuits: Comparator and Summing Amplifiers

This section identifies the use of positive feedback in op-amp circuits. Analyze the operation of several basic comparator circuits and the operation of several types of summing amplifiers.

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Key Concepts

  • Hysteresis
  • Schmitt trigger
  • Comparator
  • Summing amplifier
  • Digital-to-analog converter
  • Comparators operate with open-loop gain.
  • The output is limited by the power supply voltage applied to the circuit.
  • Noise levels are usually the same at both the inverting and non-inverting inputs.
  • An op-amp comparator that uses hysteresis is called a Schmitt trigger.
  • Noise at the input of the comparator can cause inadvertent output transitions.
  • Hysteresis (positive feedback) is used to minimize the impact of noise on the comparator output.
  • A summing amplifier can be scaled to apply unity gain to all inputs.
  • A summing amplifier can be scaled to apply greater than unity gain to all inputs.
  • A summing amplifier can be scaled to apply differing gains to the inputs (scaling adder).
  • The use of negative feedback has a major impact on the input and output impedance that can be far different than the design parameters.

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