Question

A triode has mutual conductance = 2.0 millimho and plate resistance $=20K\Omega$ It is desired to amplify a signal by a factor of 30. What load resistance should be added in the circuit?

Answer 1

Here $r_p=20K\Omega$
= Plate resistance
Mutual Conductance $=g_m$
= 2.0 milli mho
$=2\times {10}^{-3}mho$
Amplification factor, $\mu =30$
Load Resistance $=R_L=?$
We Know $A=\frac{\mu }{1+\frac{r_p}{R_L}}$
Where A = Voltage amplification factor.
$A=\frac{r_p\times g_m}{1+\frac{r_p}{R_L}}.Where\mu =r_p\times g_m\Rightarrow 30=\frac{20\times {10}^3\times 2\times {10}^{-3}}{1+\frac{20000}{R_L}}\Rightarrow 3=\frac{4R}{R_L+20000}\Rightarrow 3R_L+60000=4R_L{R}_L=60000\Omega =60K\Omega$