12.19 : トランジスタ

The MOSFET operates as a voltage-controlled current source in its active region, where the gate-to-source voltage regulates the drain current.

This transconductance MOSFET amplifier can be converted into a voltage amplifier by directing the output current through a resistor.

The output voltage is obtained by subtracting the voltage drop across the load resistance from the supply voltage. This results in an inverted version of the output voltage, shifted by the supply voltage.

The voltage-transfer characteristic plot of the amplifier illustrates the relationship between the output drain and input gate voltage.

It highlights the amplifier's active region, with a steep slope for maximum gain but a nonlinear drain voltage.

Applying a gate-to-source DC voltage bias at the quiescent point within the active region typically results in nearly linear amplification from the MOSFET.

When a small, time-varying signal is applied to the amplifier, it overlays onto the DC bias voltage around the Q-point.

The MOSFET operates within a short, nearly linear segment of the characteristic curve, resulting in an amplified output drain voltage.