Low frequency analysis of FET amplifier

Low frequency analysis of FET amplifier:

From above figure, it has two RC networks that affect its gain as the frequency is reduced below midrange. These are,

1.     RC network formed by the input coupling capacitor C₁ and input impedance of the amplifier.

2.     RC network formed by the output coupling capacitor and the output impedance looking in at the drain.

`Input RC network:

Lower critical frequency of this network is given as,

The value of R_in(gate) can be determined from the data sheet as follows:

The phase shift in low frequency input RC circuit is θ = tan^-1 (X_C1 / R_in )

Output RC network:

Lower critical frequency of this network is given as,

The phase shift in low frequency output RC circuit is θ = tan^-1 (X_C2 / R_D + R_L)