Pole movements in Colpitts Oscillator
S Guha Mallick, Somnath Chatterjee, B.N. Biswas · 2015
A Colpitts oscillator is a third order nonlinear feedback control system which is required to generate steady state oscillation starting from an infinitesimal small excitation. It indicates that the pair of conjugate poles must lie on the right half side of the Laplace s-plane and third one must be in the left half of s-plane. Notwithstanding the popularity of the Colpitts oscillator some of the questions relating to its large signal analysis have remained unattended. (1) How do the poles move during the growth period of the oscillation and on what parameters the pole movement depend? (2) Do these poles ultimately reside on the imaginary axis? (3) How does the feedback delay affect the steady state amplitude of oscillation? How does the feedback delay affect the movement of the poles? (4) Simple yet elegant energy balance principle instead of nonlinear analysis has been applied to find the steady state amplitude of oscillation. These are some of the unanswered questions that the present paper deals with. Interesting simplified but accurate theory based on the operation of the oscillator near the resonant frequency of the tank circuit has been proposed.