What is a common-gate amplifier?
1 Answer
A common-gate amplifier is one of the three basic configurations of a field-effect transistor (FET) amplifier, along with common-source and common-drain (source follower) configurations. It is used to amplify voltage signals and is commonly employed in electronic circuits.
In a common-gate amplifier, the gate terminal of the FET is the input, the drain terminal is the output, and the source terminal is common to both input and output. This means that the input signal is applied to the gate terminal, and the output is taken from the drain terminal, while the source terminal is grounded or connected to a fixed potential.
Key characteristics of the common-gate amplifier include:
High input impedance: The gate terminal is reverse-biased, resulting in a high input impedance. This makes the common-gate amplifier suitable for interfacing with high-impedance sources.
Low output impedance: The output is taken from the drain terminal, which exhibits low output impedance. This makes it suitable for driving low-impedance loads.
Inverting amplifier: The common-gate configuration introduces a 180-degree phase shift between the input and output signals, making it an inverting amplifier.
Voltage gain: The voltage gain of a common-gate amplifier can be controlled by external resistors connected in the circuit. The gain is typically less than unity (less than 1) in magnitude.
Common-gate amplifiers find applications in various analog circuits, such as RF (radio frequency) amplifiers and frequency mixers. They are commonly used in communication systems, signal processing, and audio amplification where high input impedance and moderate voltage gain with a degree of inversion are required.
In a common-gate amplifier, the gate terminal of the FET is the input, the drain terminal is the output, and the source terminal is common to both input and output. This means that the input signal is applied to the gate terminal, and the output is taken from the drain terminal, while the source terminal is grounded or connected to a fixed potential.
Key characteristics of the common-gate amplifier include:
High input impedance: The gate terminal is reverse-biased, resulting in a high input impedance. This makes the common-gate amplifier suitable for interfacing with high-impedance sources.
Low output impedance: The output is taken from the drain terminal, which exhibits low output impedance. This makes it suitable for driving low-impedance loads.
Inverting amplifier: The common-gate configuration introduces a 180-degree phase shift between the input and output signals, making it an inverting amplifier.
Voltage gain: The voltage gain of a common-gate amplifier can be controlled by external resistors connected in the circuit. The gain is typically less than unity (less than 1) in magnitude.
Common-gate amplifiers find applications in various analog circuits, such as RF (radio frequency) amplifiers and frequency mixers. They are commonly used in communication systems, signal processing, and audio amplification where high input impedance and moderate voltage gain with a degree of inversion are required.