Basic Types of Feedback Amplifiers, Method of Feedback Amplifier Analysis
Basic Types of Feedback Amplifiers
There are four types of feedback amplifiers. Why?
Output sampled can be a current or a voltage
Quantity fed back to input can be a current or a voltage
Four possible combinations of the type of output sampling and input feedback
One particular type of amplifier, e.g. voltage amplifier, current amplifier, etc. is used for each one of the four types of feedback amplifiers.
Feedback factor f is a different type of quantity, e.g. voltage ratio, resistance, current ratio or conductance, for each feedback configuration.
Before analyzing the feedback amplifier’s performance, need to start by recognizing the type or configuration.
Terminology used to name types of feedback amplifier, e.g. Series-shunt
First term refers to nature of feedback connection at the input.
Second term refers to nature of sampling connection at the output.
Method of Feedback Amplifier Analysis
Recognize the feedback amplifier’s configuration, e.g. Series-shunt
Calculate the appropriate gain A for the amplifier, e.g. voltage gain.
This includes the loading effects of the feedback circuit (some combination of resistors) on the amplifier input and output.
Calculate the feedback factor f
Calculate the factor f A and make sure that it is: 1) positive and 2) dimensionless
Calculate the feedback amplifier’s gain with feedback Af using
Calculate the final gain of interest if different from the gain calculated, e.g. Current gain if voltage gain originally determined.
Determine the dominant low and high frequency poles for the original amplifier, but taking into account the loading effects of the feedback network.
Determine the final dominant low and high frequency poles of the amplifier with feedback using