Question

In a silicoo transistor, base current is charged by $20{\mu }_A$. This results is a charge of 0.02 V in base emitter voltage and a change of $2mA$ in the collection current.
(a) Find the input resistance Base and trans-conductance of the transistor.
(b) The transistor is used as an amplifier with the load resistance 5 kz. What is the voltage gain of the amplifier?

Answer 1

$R_i=\frac{\Delta V_i}{\Delta I_b}=\frac{0.02V}{20\mu A}=1000\Omega =1k\Omega$

${\beta }_{a.c.}=\frac{\Delta I_c}{\Delta I_b}=\frac{2mA}{20\mu A}=100$

$g_m=\frac{\Delta I_c}{\Delta V_i}=\frac{2mA}{0.02V}=\frac{2\times {10}^{-30}}{0.02}=0.1{\Omega }^{-1}$

$A_V={\beta }_{a.c}.\frac{R_0}{R_i}=100\times \frac{5k\Omega }{1k\Omega }=500$