Question

The intrinsic gain $A_o$ of a BJT is defined as the maximum gain a practical BJT can deliver and is formulated as $A_o=gmr{}_o.$ If the early voltage $V_A$ is measured to be 100 V at 27°C, then the value of intrinsic gain of the BJT $A_o$ equal to _____ kV/V.

• A. 3.867
• B. 2.9
• C. 3.1
• D. 4.5

Answer 1

The correct option is A 3.867

$A_o=g_{m}r{{}^{\prime }}_o.$

now $g_m=\frac{I_C}{V_T}$

and $r_o=\frac{V_A}{I_C}$

$\therefore$ $A_o=\frac{V_A}{V_T}$

now, $V_A$ = 100 given, $V_T=\frac{kT}{q}$
T = 27 + 273 = 300°K

$\therefore V_T=\frac{300}{11600}=25.76mV$

$\therefore A_o=\frac{100\times 1000}{25.86}=3.867kV/V$