19.1.1. Small Signal Equivalent Circuit

Try these first

1. 1.

   What does the small signal equivalent circuit aim to achieve?

   Hint

   Consider the linearization of circuit behavior.

2. 2.

   Define transconductance in your own words.

   Hint

   Think about current versus voltage relationships.

3. 3.

   What does transconductance measure?

   • Change in collector current per change in base-emitter voltage
   • Change in base current per change in collector-emitter voltage
   • Change in output power per change in input power

   Hint

   Focus on the relationship between current and voltage.

4. 4.

   Is the output conductance of a BJT a measure of how collector current changes with collector-emitter voltage?

   • True
   • False

   Hint

   Think about how voltage affects current.

5. 5.

   Consider a BJT amplifier with a transconductance of 1.5mS and a base-emitter resistance of 200Ω. If the input signal is a sinusoidal voltage of 20mV, calculate the output voltage swing when coupled with a load resistance of 1kΩ.

   Hint

   Use the formula for finding output voltage in small signal analysis.

6. 6.

   Given a BJT operates with a small signal current gain of 150 at a certain operating point. If the base current is 10μA, what will be the collector current? How will this value change if the operating point shifts causing β to drop to 120?

   Hint

   Recall the relationship between Ic and Ib through β.