I am trying to do a small signal analysis for the following circuit
I did not have any experience with BJT so I am having a hard time to analyze the circuit. From research, I know Q1 is common base and Q2 and Q3 are common emitter. To draw the small signal model, I would have to short all DC source and capacitors.
Then I ended up with the following circuit
I am not sure what to do next. I tried to break the circuit into 3 parts to analyze but I am not sure what to do with the 47K, 56K,15K resistors that's connected to Q1.
Can anyone help with the small signal analysis?
Now I have this for the first part if I were to divided the circuit to 3 parts.
To find the input impedance, applying KCL then it would be 12/47k + gmVpi + Vpi/rpi + Vin/10K?
I am a bit confused with Vpi and rpi. Do I need to calculate that or it's from the BC547 data sheet?