I was reading an Article of LC-Tuned Oscillators in Microelectronics Circuits (By Sedra Smith).
I came across the the Colprit Oscillator. I did the simulation of the circut given in exerciseto understand it.
I dont understand How Colprit Oscilator Satisfy Barkhausen criterion?
The book says "Detailed analysis of amplitude control, which makes use of nonlinear-circuit techniques, is beyond the scope of this book". Does their is any reference to understand it in simple way.
Best Answer
The Oscillation Criterion (Barkhausen) requires that the magnitude of the loop gain (turn-around gain within the complete feedback loop) is somewhat larger than "1" (0 dB) with a phase shift of exactly 0 deg (-360 deg) at one single frequency only. In the shown circuit this is accomplished by the amplifier (common emitter stage with 180deg phase shift) and the L-C combination in the collector path (additional 180 deg at resonance). Feedback to the base is accomplished by the capacitor C3.
However, each oscillator with a loop gain >1 will generate a sinusoidal signal with rising amplitudes with hard-limiting caused by the fixed supply voltage. As a consequence, the signal will have much distortions (bad THD). For this reason, it is wise to incorporate an amplitude-sensitive part or circuitry which causes "soft-limiting" of amplitudes. This will automatically reduce the loop gain to the theoretical (ideal) value of "1". For this purpose, you can use diodes, thermistors, FET`s (as resistors) or other non-linear (amplitude-sensitive) devices.