shown in figure $V_{BE}=0.7V, β=100, V_A=∞$

Mumbai University > EXTC > Sem 3 > Analog Electronics 1

Marks: 10 M

Year: Nov 2013

1. For DC equivalent circuit Capacitors are open circuited hence $R_S$ and $R_L$ are not part of DC circuit as shown in Fig2.

Fig1 DC equivalent circuit of amplifier

• Applying KVL to emitter base- loop

  $-I_BR_B-V_{BE}-I_ER_E+V_{EE}=0$

  $V_{EE}- V_{BE}= I_BR_B - I_ER_E$

  $V_{EE}-V_{BE}= I_BR_B+ (β +1)I_BR_E$

  $I_B=\frac{V_{EE}-V_{BE}}{R_B+(β +1)R_E}$

  $I_B={20-0.7}{100k+(101×2k)}$

  $I_B={19.3}{302k}$

  $I_B=63.9µA$

  $I_C= β I_B$

  $I_C=6.39mA$

  $I_E= (β +1)I_B$

  $I_E= (101×63.9µA)$

  $I_E=6.453mA$

2. alculation for $g_m,Ro,Ri,Av$

• $g_m=\frac{I _C}{V_T}$

  Let $V_T=26mV$

  $g_m =\frac{6.39m}{26m}$

  $g_m =245mS$

• $r_e=\frac{V_T}{I_E}$

  $r_e= 4.029Ω$

• $R_i$ for common base is given by,

  $R_i= R_E ||r_e$

  $R_i=4.020Ω$

• Voltage gain is given by

  $A_V=\frac{RC||RL}{re}$

  $A_V=\frac{729.72}{4.029}$

  $A_V=181.11$

• Output resistance

  $Ro=R_C||R_L$

  $Ro=2.7kΩ||1kΩ$

  $Ro=729.72Ω$

$$\boxed { AV=181.11 , Ri=4.02Ω\\ gm =245mS , Ro=729.72Ω }\qquad$$