19.1.2. Equivalent Circuit of Common Emitter Configuration

Try these first

1. 1.

   Define transconductance and explain how it is calculated.

   Hint

   Think about the characteristics curve of the BJT.

2. 2.

   What does $r_{π}$ represent?

   Hint

   Use the formula $V_T / I_B$ for calculation.

3. 3.

   What does transconductance ($g_m$) measure?

   • The change in collector current with respect to $V_{BE}$
   • Base-emitter resistance
   • Output conductance

   Hint

   Think about the relationship between input voltage and output current.

4. 4.

   True or False: The Q-point is irrelevant when analyzing small signal models.

   • True
   • False

   Hint

   Recall the definition of Q-point.

5. 5.

   A BJT operates with an $I_C = 5 mA$, and at a given Q-point, you need to determine $g_m$ if $V_T = 25mV$. Construct the small signal model and analyze.

   Hint

   Recall the relationship of $g_m$ in terms of $I_C$ and $V_T$.

6. 6.

   Given BJT characteristics, define the implications of varying $g_o$ in terms of its impact on output current with changes in $V_{CE}$.

   Hint

   Explore the passive effects of Early voltage on collector current behavior.