<Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations . (January 2018) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations . (January 2018) (Learn how and when to remove this template message) </Td> </Tr> <P> In electronics, a common - source amplifier is one of three basic single - stage field - effect transistor (FET) amplifier topologies, typically used as a voltage or transconductance amplifier . The easiest way to tell if a FET is common source, common drain, or common gate is to examine where the signal enters and leaves . The remaining terminal is what is known as "common". In this example, the signal enters the gate, and exits the drain . The only terminal remaining is the source . This is a common - source FET circuit . The analogous bipolar junction transistor circuit may be viewed as a transconductance amplifier or as a voltage amplifier . (See classification of amplifiers). As a transconductance amplifier, the input voltage is seen as modulating the current going to the load . As a voltage amplifier, input voltage modulates the amount of current flowing through the FET, changing the voltage across the output resistance according to Ohm's law . However, the FET device's output resistance typically is not high enough for a reasonable transconductance amplifier (ideally infinite), nor low enough for a decent voltage amplifier (ideally zero). Another major drawback is the amplifier's limited high - frequency response . Therefore, in practice the output often is routed through either a voltage follower (common - drain or CD stage), or a current follower (common-gate or CG stage), to obtain more favorable output and frequency characteristics . The CS--CG combination is called a cascode amplifier . </P> <P> At low frequencies and using a simplified hybrid - pi model, the following small - signal characteristics can be derived . </P>

Difference between common source common gate and common drain amplifier
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