Determine the current and voltage gains for the two-stage capacitor-coupled amplifier shown in **fig. 1**.

**Fig. 1 **

**Solution: **

We develop the hybrid equivalent circuit for the multistage amplifier. This equivalent is shown in **fig. 2**. Primed variables denote output stage quantities and unprimed variables denote input stage quantities.

**Fig. 2**

Calculations for the output stages are as follows

For the input stage,

The input resistance is determined as:

The current gain, A_{i}, can be found by applying the equations derived earlier, where the first stage requires using the correct value for R_{load} derived form the value of R_{in} to the next stage.

Alternatively, we analyze **fig. 2** by extracting four current dividers as shown in **fig. 3**.

**Fig. 3**

The current division of the input stage is

The output of the first stage is coupled to the input of he second stage in **fig. 3(b)**. The input resistance of the second stage is

The current in R'_{in} is i_{load} and is given by

Again, i _{load} is current-divided at the input to the second stage. Thus,

The output current is found from **fig. 3(c)**:

The current gain is then

A_{i} =927

Now using the gain impedance formula, we find the voltage gain:

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