FET Common Source Amplifier Circuit

- details of the common source amplifier circuit based around FET technology.

Common source FET configuration is probably the most widely used of all the FET circuit configurations.

Like its bipolar counterpart the common emitter circuit, the FET common source amplifier provides a good level of all round performance for many applications.

The common source circuit provides a medium input and output impedance levels. Both current and voltage gain can be described as medium, but the output is the inverse of the input, i.e. 180° phase change. This provides a good overall performance and as such it is often thought of as the most widely used configuration.

Basic common source FET circuit diagram
Basic diagram of the common source FET amplifier circuit

Common source FET amplifier characteristics summary

The table below gives a summary of the major characteristics of the common source amplifier.

Common source amplifier characteristics
Parameter Amplifier Characteristics
Voltage gain Medium
Current gain Medium
Power gain High
Input / output phase relationship 180°
Input resistance Medium**
Output resistance Medium

** Note: the input resistance for a FET itself is very high in view of the fact that it takes virtually no current.

By Ian Poole

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