Question
Download Solution PDFThe given circuit represents small signal model of:
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFCommon Gate FET Amplifier:
In this amplifier configuration, the input signal is applied to the source terminal, and output is taken from the drain as shown in Fig.
The gate is grounded, RL is in series with drain, and a source resistance RS is included in the circuit across which Vi is
dropped.
The ac equivalent circuit is shown in Fig. below where the current source is connected between the drain and the source terminals.
Since source and drain are the input and output terminals respectively, (gmVgs) appears between the input and the output.
Additional Information
(i) Voltage Gain:
It is the same as the gain for a common source amplifier except that it is a positive quantity. It means that Vo and Vi are in phase
Vo = id × (rd || RL) =
We have, id = gm Vgs = gm Vi
⇒ Vo =
Now, Gain(AV) =
(ii) Input Resistance:
If we neglect current through RS, then input current is given by,
id = gm Vgs = gm Vi
Now input resistance (Ri) =
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