An apparatus and method for using negative FM feedback in high quality oscillator devices

摘要

An apparatus and method are provided for increasing the effective Q-value of an oscillator so that the required Q-value can be reached with the use of a low Q-value oscillator. In this apparatus and method, the FM noise is measured at the output of the oscillator by an FM detector and the output of the FM detector is fed back to the control input of the oscillator. By using this negative FM feedback, frequency variations in the oscillator output are suppressed by applying a correction signal at the control input of the oscillator. The amount of suppression depends on the loop gain of the FM feedback loop and the amount of suppression is proportional to the loop gain so that the effective Q-value of the oscillator is proportional to the loop gain. As a result of correcting the FM noise measured at the oscillator output by using a negative FM feedback loop, the effective Q-value of the oscillator corresponds to the original Q-value multiplied by the loop gain of the FM feedback loop so that the effective Q-value of the oscillator is increased.