MOSFET output resistance

The MOSFET is a three-terminal semiconductor device, every active electronic component shows its resistance.

The resistance property shown by the MOSFET is due to the presence of charged particles at each of the layers such as source, gate, and drain. And the gate is considered as the input of the MOSFET and the source is the output of the MOSFET.

When we apply Ohm’s law, resistance is the result of voltage and current at the circuit, the voltage applied to the device result in a current flow is happened at the source and the resistance at the source terminal is considered as the output resistance of the MOSFET.

Output resistance MOSFET 

The output resistance will the resistance of the source and gate terminal at the time when the voltage is applied to the MOSFET.

Id = gm vgs + Vds/ro

gm= 2k(Vgs-Vt)

ro= 1/λk(Vgs-vt)2

  The output resistance is equal to = 1/ λ ID

Finite output resistance MOSFET 

The MOSFET had finite or limited output resistance at saturation mode and active mode of operation.

The resistance at any device will be functioned by the flow of current at the channels, this is possible due to the formation of the electric field by the charged carrier. 

At the MOSFET all the operation begins with the threshold voltage which results from a current flow at the source with minimum resistance.

And the finite resistance at MOSFET is also due to the channel length modulation process.

Small signal output resistance MOSFET 

The normal output resistance ‘Ro’ is independent of small signals or any other signals.

Therefore, small-signal output resistance is the resistance that we can spot at the output on applied small signal input.

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