Systems and Methods for Maintaining a Drive Signal to a Resonant Circuit at a Resonant Frequency

A system for maintaining a drive signal to a resonant circuit at a resonant frequency comprising:

• an oscillator configured to provide an output to a phase comparator, a drive circuit having variable gain, and a low-pass filter, the drive circuit configured to provide a drive signal to a resonant circuit, the low-pass filter having a characteristic frequency that is about the same as the resonant frequency of the resonant circuit;
• a phase detector configured to receive a filtered signal from each of the low-pass filter and the resonant circuit, and responsively provide a phase-indicating signal to the phase comparator representing the phase of whichever of the phase detector inputs is stronger;
• and
• the phase comparator, wherein the phase comparator is configured to provide a signal based on the phase difference between the oscillator output and the phase-indicating signal, wherein the signal from the phase comparator is used to control the frequency of the oscillator such that the phase difference converges to about a ninety degree phase shift between the oscillator output and the phase-indicating signal, thereby maintaining the drive signal to the resonant circuit at about the resonant frequency.

A method for maintaining a drive signal to a resonant circuit at a resonant frequency comprising:

• using an oscillator to provide an output to a phase comparator and a drive circuit, the drive circuit configured to provide a drive signal to a resonant circuit;
• using a phase detector to receive a filtered version of the drive signal from the resonant circuit and provide a phase-indicating signal to the phase comparator;
• using the phase comparator to provide a signal based on the phase difference between the oscillator output and the phase-indicating signal;
• and
• using the signal from the phase comparator to control the frequency of the oscillator such that the phase difference converges to a fixed value.

A method for maintaining a drive signal to a resonant circuit at a resonant frequency comprising:

• using an oscillator to provide an output to a phase comparator, a drive circuit having variable gain, and a low-pass filter, the drive circuit configured to provide a drive signal to a resonant circuit, the low-pass filter having a characteristic frequency that is about the same as the resonant frequency of the resonant circuit;
• using a phase detector to receive a filtered signal from each of the low-pass filter and the resonant circuit, and responsively provide a phase-indicating signal to the phase comparator representing the phase of whichever of the phase detector inputs is stronger;
• using the phase comparator to provide a signal based on the phase difference between the oscillator output and the phase-indicating signal;
• and
• using the signal from the phase comparator to control the frequency of the oscillator such that the phase difference converges to about a ninety degree phase shift between the oscillator output and the phase-indicating signal, thereby maintaining the drive signal to the resonant circuit at about the resonant frequency.