Op-Amp Responses

This chapter identifies the basic areas of op-amp responses and analyzes the open- and closed-loop responses of an op-amp.

Key Concepts

• Open-loop vs closed-loop gain
• Open-loop frequency and phase response
• Closed-loop frequency and phase response
• Phase-lag compensation
• Bandwidth
• Phase shift
• Loop gain
• Phase margin
• The gain of an op-amp amplifier is dependent upon frequency.
• Unity-gain bandwidth is the frequency at which the output is equal to one or unity.
• The internal R-C networks in an op-amp causes a phase shift between the input and the output.
• Each internal stage affects the frequency response.
• Each internal stage adds to the overall phase lag between the input and the output.
• An uncompensated op-amp is one which has more than one critical frequency.
• All op-amps have designed input and output impedances.
• The use of negative feedback has a major impact on the input and output impedance that can be far different from the design parameters.
• Compensation is used to eliminate open-loop roll-off rates.
• Compensation is used to extend the -20dB/decade rate to a lower gain amplifier.
• A compensation network consists of an RC network.

opampgainvsfreq.jpg

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