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CS Amplifier with Current Source Load :

Figure below shows the circuit diagram of CS amplifier with current source load. In this a current source is made by using a PMOS transistor operated in saturation mode by using a Gate bias V_b. The small signal model of this circuit is also shown in Figure below

The equivalent circuit can be drawn as shown in figure below

By applying KVL, V_in = V_GS1

By applying KCL at node A

g_m1 V_GS1 + + = 0

\ g_m1 V_in = - V_out

\ = A_n = - g_m1 (ro₁ || ro₂)

In order to derive the output impedance consider the circuit shown in Figure below.

\ By applying KCL at node A,

We get, g_m1 V_GS1 + + = I_x

V_x = I_x [ V_GS1 = 0]

\ = R_out =

\ R_out = (ro₁ || ro₂)

\ Hence the output impedance of current source load of CS amplifier is ro ₁ || ro₂.