Question

For a CE-transistor amplifier, the audio signal voltage across the collected resistance of 2 kΩ is 2 V. Suppose the current amplification factor of the transistor is 100, find the input signal voltage and base current, if the base resistance is 1 kΩ.

Answer 1

Collector resistance, RC = 2 kΩ = 2000 Ω 
Audio signal voltage across the collector resistance, V = 2 V 
Current amplification factor of the transistor, β = 100 
Base resistance, RB = 1 kΩ = 1000 Ω 
Input signal voltage = V_i 
Base current = I_B 
We have the amplification relation as:
Voltage amplification =\(\frac{ V}{V_i} =β\frac{R_c}{R_b}\)
V_i = \(\frac{V}{β}\) \(\frac{R_B}{R_C}\)
V_i = \(\frac{2\times 1000}{100\times 2000}\)
V_i = 0.01 V
Therefore, the input signal voltage of the amplifier is 0.01 V. 
Base resistance is given by the relation:
R_B =\( \frac{V_i}{I_B}\)
R_B = \(\frac{0.01}{1000}\)
R_B = \(10\times10^{-6} A\)
R_B = 10\( μA\)
Therefore, the base current of the amplifier is 10 \(µA\).