Bridge-stabilized oscillator circuit and method

Method for stabilizing an oscillator signal generated from an oscillator circuit comprising the steps of:

• operating a resonator at variable vibration frequencies including a resonance frequency;
• connecting the resonator to form one arm of a discriminating bridge circuit, wherein the resonator when free standing outside the bridge circuit has impedance characteristics dependent upon its vibration frequency;
• and the bridge circuit has an impedance;
• arranging the bridge circuit so that its impedance at a first node of the bridge circuit has the same impedance characteristics as the free standing resonator;
• producing at the first node of the bridge circuit a first bridge signal having a phase;
• producing at a second node of the bridge circuit a second bridge signal having a phase shift which leads or lags the phase of the first bridge signal by a first prescribed phase shift when the resonator is vibrating respectively above or below its resonance frequency;
• phase shifting the second bridge signal by a second prescribed phase shift and generating an RF signal;
• mixing the first bridge and the RF signals in a synchronous demodulator stage and generating an error signal having states representing when the resonator is vibrating above, equal to and below its resonance frequency;
• converting the error signal to a control signal and transmitting the control signal to an oscillator stage having first, second, and third terminals;
• operating the oscillator stage to respond to the states of the control signal being applied to the first terminal so that when the resonator is initially vibrating above, equal to, or below its resonance frequency the vibrating frequency of the resonator will subsequently be reduced, kept unchanged, or increased respectively towards the resonance frequency;
• connecting the second terminal to the first node;
• and
• operating the oscillator stage to respond to the resonator for generating the oscillator signal at the third terminal.

An oscillator comprising:

• a resonator having an Equivalent Series Resistance (ESR) and a resonant frequency that is a function of an excitation current;
• a circuit for generating a programmable negative resistance;
• a resonant series LC circuit having inductive and capacitive elements and a voltage appearing at a terminal located between the inductive and capacitive elements;
• a voltage detector connected to the terminal and used to program the value of the negative resistance to be equal to the ESR, such that the negative resistance produces a fixed value of the voltage at the terminal resulting in a desired value of current for exciting the resonator.

Method for stabilizing an oscillator signal produced by an oscillator circuit comprising the steps of:

• exciting a resonator into resonant frequency via the application of an excitation current;
• the resonator having an Equivalent Series Resistance (ESR);
• generating a programmable negative resistance;
• configuring a resonant series LC circuit with inductive and capacitive elements and generating a voltage at a terminal located between the inductive and capacitive elements;
• responding to the voltage for programming the value of the negative resistance to be equal to the ESR such that the negative resistance produces a fixed value of the voltage at the terminal resulting in a desired value of current for exciting the resonator.