Question 10.3: Simplified Model for an Amplifier Cascade Find the overall s...
Simplified Model for an Amplifier Cascade
Find the overall simplified model for the cascade connection of Figure 10.6.
First, determine the voltage gain of the first stage accounting for loading by the second stage.
The voltage gain of the first stage, accounting for the loading of the second stage, is
A_{v1}=A_{voc1}\frac{R_{i2}}{R_{i2}+R_{o1}} =150
With an open-circuit load, the gain of the second stage is
A_{v2}=A_{voc2}=100
The overall voltage gain is the product of the gains of the separate stages.
The overall open-circuit voltage gain is
A_{voc}=A_{v1}A_{v2}=15 \times 10^3
The input resistance of the cascade amplifier is
R_1=R_{i1}=1 \text{ M}\Omega
and the output resistance is
R_o=R_{o2}=100 \ \Omega
The input impedance is that of the first stage, and the output impedance is that of the last stage.
The simplified model for the cascade is shown in Figure 10.7
