I want to find the AC equivalent circuit. Now, the rules I apply are
- Short the DC voltages
- Short-circuit the capacitors
- Open-circuit the inductors
- Find amplifier parameters.
My questions are the following.
- Why is C1 still left in the circuit?
- I assumed the current would be beta * Ib. But they are using gm * Vpi. I know gm = Ic/Vt, with Vt = 26mV. However, I am confused on which convention to use. Or are they both the same thing?
- Why is gm multiplied by Vpi? If it's voltage controlled current source, then shouldn't it be gm * Vo?
- Lastly, would Re be calculated by doing Vo/Ie or Vt / Ie?
Different sources are giving me different ways of answering my questions and I want to narrow down to the most accurate method.