FET Common Gate Amplifier Circuit

- details of the common gate circuit that can be designed using a field effect transistor, FET.

Common gate FET configuration provides a low input impedance while offering a high output impedance.

Although the voltage gain is high, the current gain is low and the overall power gain is also low when compared to the other FET circuit configurations available.

The other salient feature of this configuration is that the input and output are in phase.

 Common gate FET amplifier circuit diagram
Common gate FET amplifier circuit

The circuit is not as widely sued as other FET configurations, but it is used where a low input is needed to provide a good match. Some examples of instances where the common gate amplifier may be used are for low impedance microphone preamplifiers and for VHF / UHF RF amplifiers.

Common gate amplifier characteristics summary

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

Common gate transistor amplifier characteristics
Parameter Characteristics
Voltage gain High
Current gain Low
Power gain Low
Input / output phase relationship
Input resistance Low
Output resistance High

By Ian Poole

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