26.3.2. Sensitivity to β Variation

Try these first

1. 1.

   What does β represent in a transistor?

   Hint

   Think about the definition relating to current.

2. 2.

   What is the primary advantage of self-biasing over fixed bias?

   Hint

   Consider the impact of varying parameters.

3. 3.

   What role does the emitter resistor play in a self-biased amplifier?

   • Offers stability against β variation
   • Increases the gain
   • Decreases the input impedance

   Hint

   Consider the main reason for its inclusion.

4. 4.

   True or False: In a fixed bias configuration, the collector current is less sensitive to β changes than in self-bias.

   • True
   • False

   Hint

   Think about how changes in β affect the circuit.

5. 5.

   Given a fixed bias amplifier with β = 100 and I_B = 0.1 mA, calculate I_C. Then, evaluate how a decrease in β to 80 affects I_C.

   Hint

   Use the formula carefully and re-evaluate with the new β value.

6. 6.

   Design a self-biased amplifier circuit and illustrate how the stability is maintained against β variations with a numerical example.

   Hint

   Consider setting R_E to be significantly smaller than the effective resistance derived from the β changes.