Colpitts oscillator and transconductance value

Thread Starter

Iza Soliwoda

Joined Sep 2, 2015
Hello! Can you give me a hint to answer this question? This is part of an exam task. The first part was to identify input impedance, which I did.
"For what values of parameters (gm, I1) circuit can (regardless of the small changes of voltage and current supply and the temperature) generate periodic output voltage signal?" I searched for this whole night and failed to answer it. What I found is that:
Magnitude criterion for steady-state oscillation at the oscillation frequency f is given by
|T (f)| = 1
In order for the oscillations to start and grow, the magnitude of the loop gain T must be greater than unity.
(I had to translate it from Polish to English, so I hope everything is understandable and sorry for any mistakes :). )