Question

For $CE$ transistor amplifier, the audio signal voltage across the collector resistance of $2 k \Omega$ is $4\, V$. If the current amplification factor of the transistor is $100$ and the base resistance is $1 \, k\Omega$, then the input signal voltage is

• A. 10 mV
• B. 20 mV
• C. 30 mV
• D. 15 mV

Answer 1

The Correct Option is B

To find the input signal voltage for a common-emitter (CE) transistor amplifier, given the audio signal voltage across the collector resistance, current amplification factor, and the base resistance, we can proceed through the following steps:

1. First, understand the given parameters:
   • Collector resistance, R_C = 2 \, k\Omega
   • Voltage across collector resistance, V_{RC} = 4 \, V
   • Current amplification factor (or current gain), \beta = 100
   • Base resistance, R_B = 1 \, k\Omega
2. Use the relationship between collector current change and base current change in a CE transistor, as given by the current amplification factor:
   I_C = \beta \cdot I_B
3. Determine the change in collector current, \Delta I_C, using the given voltage across the collector resistance:
   \Delta I_C = \frac{V_{RC}}{R_C} = \frac{4 \, V}{2 \, k\Omega} = 2 \, mA
4. Calculate the change in base current, \Delta I_B, using the relationship \Delta I_C = \beta \cdot \Delta I_B:
   \Delta I_B = \frac{\Delta I_C}{\beta} = \frac{2 \, mA}{100} = 20 \, \mu A
5. Calculate the input signal voltage, V_{in}, using the change in base current and the base resistance:
   V_{in} = \Delta I_B \cdot R_B = 20 \, \mu A \cdot 1 \, k\Omega = 20 \, mV

Therefore, the input signal voltage is 20 mV. This is the correct answer to the given question.