The MOSFET common source amplifier is the topic we discuss in this post, common source MOSFET circuit configuration is used as voltage amplifier or Transconductance amplifier schematic in electronic.
Common source MOSFET amplifier circuit
- The C1 and C2 coupling capacitors are for a couple of AC signals and filter out DC from the signal, C1 capacitor at the input, and C2 capacitor at the output.
- R1 and R2 resistors are biasing components from the voltage divider network.
- The RD resistor is used to fix the proper current at the amplifier circuit
MOSFET common source amplifier theory
In the MOSFET common source amplifier, we can see the source terminal is grounded, the circuit input is between gate-source, and the output of the circuit is taken between drain-source terminals. This is why we call it a common source amplifier.
Small signal model of MOSFET common source amplifier
- Electronic small-signal model analysis was used to determine the circuit behavior.
- Using the small-signal model we can easily determine the input impedance, output impedance, voltage gain, and current gain of the MOSFET common source amplifier.
- When we apply the input voltage to the circuit an output signal appears at the drain terminal.
- We can have a source terminal for both input and output of the circuit
Voltage gain = Av = -gm rD/ 1+ gm rs
rs = swamping resistor, swamping helps to stabilize the gain and reduce solution
Current gain = Ai = Δ ioutput/iinput
The current at the common source amplifier circuit is INIFINTE or UNITY
Input impedance = Zin = RG || RGS ~ rG
The input impedance at the common source amplifier circuit is INIFINTE
Output impedance = Zin = Zin (gate) || RG
The output impedance is mainly dependent on RD drain resistance