The working concept of PMOS (p-type metal-oxide-semiconductor) is based on the use of a p-type channel and an n-type substrate. The p-type channel is created by doping the substrate with p-type impurities, and it is separated from the substrate by a thin layer of oxide. When a voltage is applied to the gate, it creates an electric field that attracts minority charge carriers (electrons) to the surface of the p-type channel, allowing for the flow of current.
Vgs (th) stands for threshold voltage for gate-source, which is the minimum voltage required to create an inversion layer in the p-type channel and start the flow of current. In PMOS, this voltage is typically negative, meaning that the gate must be at a lower potential than the source for the transistor to turn on.
In source follower mode, the PMOS transistor acts as a voltage buffer, with the source connected to the output and the drain connected to the input. When a voltage is applied to the gate, it creates an inversion layer in the p-type channel, allowing for the flow of current from the source to the drain. However, the output voltage will be slightly lower than the input voltage due to the voltage drop across the channel.
If the gate voltage is lower than the threshold voltage, the transistor will not turn on and no current will flow from the source to the drain. This is because there is not enough energy to create an inversion layer in the p-type channel and attract minority charge carriers.
In source follower mode, the output voltage will be slightly lower than the input voltage due to the voltage drop across the channel. The exact output voltage will depend on the characteristics of the transistor, such as the threshold voltage and the channel resistance.
