For each of Common Source(CS), Common Gate(CG), Common Drain(CD) ampli ers, 1. Show its operating principle
For each of Common Source(CS), Common Gate(CG), Common Drain(CD)
ampli ers,
1. Show its operating principle
2. How DC biasing can be done
Answer(a)
Operating principle of
(1) Common Source Amplifier
The figure shows a basic common-source circuit with voltage divider biasing. Here the source is at ground potential or zero potential so, It named the common source amplifier. the signal from the source is coupled into the gate of the transistor via coupling capacitor Cc. It provides the DC isolation between an amplifier and the source of the signal. and the DC biasing is done by Resistors R1 and R2. and it does not get disturbed when the signal source is capacitively coupled to the amplifier.
Here,
The output voltage is
And a source register Rs stabilizes the Q-point against any variations in the transistor. And bypass capacitor minimizes the loss in small-signal voltage gain by maintaining the Q-point stability.
So, Common source amplifier only used as voltage amplifier but voltage amplification is very low.
(2) Common drain amplifier
The above figure is the circuit diagram of the common drain amplifier which is also called the source follower amplifier
In a common drain amplifier, the input signal is applied to the gate and the output is taken from the source and drain is common for both gate and source.
So, the coupling capacitor is used on the input side to provide isolation, and output is taken through the load register.
The output voltage is
Input resistance is which is very large for the common drain amplifier.
And Common drain amplifier is used as a Voltage Buffer.
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