As we all know the satellite receiver is the most imp
part of Wireless Communication system, but we usually not thinks too much about
the internal part functioning. In this blog I have covered one of its most imp parts
(Common Source Amplifier) theoretical or technical background.
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| Satellite communication Block diagram with common source amplifier |
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.
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| Common Source Amplifier |
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| Small Signal model of common source Amplifier |
The common-source (CS) amplifier may be
viewed as a transconductance amplifier or as a voltage amplifier.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.
Common
source amplifier characteristics
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Parameter
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Amplifier Characteristics
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Voltage
gain
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Medium
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Current
gain
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Medium
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Power
gain
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High
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Input / output
phase relationship
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180°
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Input
resistance
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Medium**
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Output
resistance
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Medium
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Author - Amresh Kumar Singh
(Trainee Engineer at Silicon Mentor)
