Analysis of oscillator amplitude control, and its application to automatic tuning of quality factor for active LC filters

This paper presents an analytical solution to the amplitude control of the Q-enhanced LC resonator. It is shown that due to the nonlinearity of the active devices, effective amplitude control is realizable by a conventional magnitude-locked-loop, and that it is applicable to the automatic quality factor tuning of active LC filters. The effects of the weak nonlinearity magnitude and the amplitude used in the reference resonator on the achieved Q of filter resonator(s) is discussed. The results are verified by simulations and breadboard experiments.