I am mainly focusing on the oscillator part on the left, which I've redrawn as follows
To analyze the circuit's stability, I "broke the loop" at the base of the BJT to derive an expression for the loop gain. Unfortunately, my expression for the loop gain does not at all mirror the simulated loop gain obtained by simulating the circuit in LTSpice. From what I can tell, there are three possible sources of error:
- My small signal equivalent circuit is wrong
- Due to the oscillator's large signal swing, the linearized small signal model is not representative of the actual circuit behavior
- I did the algebra wrong.
This is the small signal equivalent circuit I used for the analysis. Does anyone see anything wrong with the way I drew it?