Question

For a CE transistor amplifier, the audio signal voltage across the collector resistance of \(2.0\,\text{k}\Omega\) is \(2.0\,\text{V}\). Suppose the current amplification factor of the transistor is 100. What should be the value of \(R_B\) in series with \(V_{BB}\) supply of \(2.0\,\text{V}\) if the base current has to be 10 times the signal current?

• A. \(14\,\text{k}\Omega\)
• B. \(18\,\text{k}\Omega\)
• C. \(10\,\text{k}\Omega\)
• D. \(5\,\text{k}\Omega\)

Hint:

Base bias current must be much larger than signal current for linear amplification.

Answer 1

The Correct Option is B

Step 1: Signal collector current: \[ i_c=\frac{2}{2000}=1\,\text{mA} \]
Step 2: Signal base current: \[ i_b=\frac{i_c}{\beta}=0.01\,\text{mA} \]
Step 3: Required base current: \[ I_B=10i_b=0.1\,\text{mA} \]
Step 4: \[ R_B=\frac{2}{0.1\times10^{-3}}\approx18\,\text{k}\Omega \]