Estimate the input resistance, output resistance, small-signal voltage gain and lower cut-off frequency of the following circuit, given that gm = 72 mS. You may assume that CS has been chosen so that its impedance is ‘small’ at the frequencies of interest.

Question

Estimate the input resistance, output resistance, small-signal voltage gain and lower cut-off frequency of the following circuit, given that [latex] g_{m} = 72 mS [/latex]. You may assume that [latex] C_{S} [/latex] has been chosen so that its impedance is ‘small’ at the frequencies of interest.

Accepted Answer

Because of the similarity between the circuits, the input resistance and output resistance of the circuit are the same as in the circuit in Example 18.5. Similarly, as the input resistance and the size of the coupling capacitor are the same as in the earlier example, the lower cut-off frequency is also the same as in Example 18.5.

The gain of the circuit is given by

\frac{v_{o}}{v_{i}} \approx -g_{m}R_{D} = -72 × 10^{-3} × 3.3 × 10^{3} = -238

The gain of the circuit is given by

[latex] \frac{v_{o}}{v_{i}} \approx -g_{m}R_{D} = -72 × 10^{-3} × 3.3 × 10^{3} = -238 [/latex]

Question 18.7: Estimate the input resistance, output resistance, small-sign......

Related Answered Questions

For the circuit in Example 18.5, compare the values obtained for the gain of the circuit when using the expressions of Equations 18.7, 18.8 and 18.9, assuming that gm = 72 mS and rd = 50 kΩ. ...

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