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For the amplifier shown in following figure, determine- 1. Gm, rd 2. Zi, Zo, Av values in each case for both with and without rd.
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Step 1 :

Calculate $r_d$ - 

$r_d=\dfrac{1}{Y_{os}}$

$\therefore r_d=\dfrac{1}{20 \times 10^{-6}}$

$\therefore r_d=50k \Omega$

 

Step 2 :

Calculate $g_m$

$\therefore g_m=\dfrac{I_D}{V_{DSQ}}$

But $I_D=\dfrac{V_{DD}-V_{DSQ}}{R_D}$

 $\therefore I_D=\dfrac{10-2.75}{3.3}=2.197mA$

$\therefore g_m=\dfrac{2.197}{2.75}=0.7989mS$

Analysis with $r_d$

 

Step 1 :

Calculate $A_V$

$\therefore A_V=\dfrac{V_0}{V_i}=\dfrac{-g_mV_{gs}(r_d\mid\mid R_D \mid\mid R_F)}{V_gs}=-g_m(r_d\mid\mid R_D \mid\mid R_F)$

$\therefore A_V=-0.7989 \times 10^{-3}[50k \mid\mid3.3k\mid\mid10M]$

$\therefore A_V=-0.7989 \times 10^{-3}\times 3.095 \times 10^3=-2.473$

 

Step 2 :

Calculate $R_{MI} \ and \ Z_i $

$R_{MI}=\dfrac{R_F}{1-A_V}=\dfrac{10M}{1+2.473}=2.879M \Omega$

$Z_i=R_{MI}=2.879M \Omega$

 

Step 3 :

Calculate $Z_0$

$\therefore Z_0=r_d \mid\mid R_D \mid\mid R_{M2}$

$\therefore Z_0=50k \mid\mid3.3k \mid\mid 10M \Omega$

$\therefore Z_0=3.095k \Omega$

Analysis without $r_d$ 

 

Step 1 :

Calculate $A_V$

$A_V=-g_m(R_D \mid\mid R_{M2}) $

$\therefore A_V= -0.7989(3.3 \mid\mid10M \Omega)$

$\therefore A_V=-0.7989 \times 3.298=-2.6355$

 

Step 2 :

Calculate  $Z_i$

$Z_i=R_{M1}=2.879M \Omega$

 

Step 3 :

Calculate $Z_0$

$\therefore Z_0=R_D \mid\mid R_{M2}$

$Z_0=3.3k \mid\mid10M \Omega$

$\therefore Z_0=3.298k \Omega$

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