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.

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