Automatic gain control of a closed loop fiber optic gyroscope using non-linear control laws

A closed loop gain control circuit for controlling the gain of a non-linear variable gain amplifier that is arranged to amplify signals output from a signal source, comprising:

• a perturbation injection circuit arranged to provide a perturbation signal ±d;
• a phase modulator connected between the perturbation injection circuit and the signal source to phase modulate signals output from the signal source;
• a variable gain amplifier arranged to receive the electrical signals indicative of optical signal signals output from the signal source and provide an amplified signal;
• a perturbation compensation circuit arranged to apply perturbation compensation signals to signals output from the variable gain amplifier, the perturbation compensation circuit being arranged to provide a compensated signal by reducing the magnitude of the perturbation in the amplified signal output from the variable gain amplifier;
• a gain error circuit connected to the perturbation compensation circuit, the gain error circuit being arranged to produce a gain error signal that indicates the magnitude of perturbation remaining in the amplified signal after perturbation compensation;
• and
• a feedback system connected between the gain error circuit and the variable gain amplifier, the feedback system being arranged to provide a gain control signal to the variable gain amplifier to reduce the magnitude of the gain error signal.

A system for processing optical signal signals output from a fiber optic gyroscope, comprising:

• a perturbation injection circuit arranged to provide a perturbation signal ±d;
• a phase modulator connected between the perturbation injection circuit and the fiber optic gyro, the phase modulator being arranged to apply the perturbation to the fiber optic gyroscope;
• a variable gain amplifier arranged to receive the electrical signals indicative of optical signal signals output from the fiber optic gyroscope and provide an amplified signal;
• a perturbation compensation circuit arranged to apply perturbation compensation signals to signals output from the variable gain amplifier, the perturbation compensation circuit being arranged to provide a compensated signal by reducing the magnitude of the perturbation in the amplified signal output from the variable gain amplifier;
• a gain error circuit connected to the perturbation compensation circuit, the gain error circuit being arranged to produce a gain error signal that indicates the magnitude of perturbation remaining in the amplified signal after perturbation compensation;
• a feedback system connected between the gain error circuit and the variable gain amplifier, the feedback system being arranged to provide a gain control signal to the variable gain amplifier to reduce the magnitude of the gain error signal;
• and
• processing circuitry connected between the perturbation compensation circuit and the phase modulator for determining the rotation rate sensed by the fiber optic gyroscope and for controlling the phase modulator to apply a rate nulling signal to the fiber optic gyroscope.

A method for controlling the gain of a non-linear variable gain amplifier that is arranged to amplify signals output from a signal source, comprising the steps of:

• arranging a perturbation source to provide dither signals of magnitude ±d;
• connecting a modulator between the perturbation source and the signal source;
• connecting a dither compensation circuit to the amplifier;
• arranging the dither compensation circuit to apply dither compensation signals having magnitude ±rd to signals output from the amplifier, the dither compensation signals being formed to reduce the magnitude of the dither in the signals output from the amplifier;
• connecting a gain error demodulator to receive signals output from the dither compensation circuit, the gain error demodulator being arranged to provide a gain error signal that indicates the magnitude of the dither in the signals output from the analog to digital converter;
• and
• connecting a feedback system to the gain control demodulator and arranged to provide a gain control signal to the variable gain amplifier to reduce the magnitude of the gain error signal.

A method for controlling the gain of a non-linear variable gain amplifier that is arranged to amplify signals output from a signal source, comprising the steps of:

• arranging a perturbation injection circuit to provide a perturbation signal ±d;
• connecting a phase modulator between the perturbation injection circuit and the signal source to phase modulate signals output from the signal source;
• arranging a variable gain amplifier to receive the electrical signals indicative of optical signal signals output from the signal source and provide an amplified signal;
• arranging a perturbation compensation circuit to apply perturbation compensation signals to signals output from the variable gain amplifier, the perturbation compensation circuit being arranged to provide a compensated signal by reducing the magnitude of the perturbation in the amplified signal output from the variable gain amplifier;
• connecting a gain error circuit to the perturbation compensation circuit, the gain error circuit being arranged to produce a gain error signal that indicates the magnitude of perturbation remaining in the amplified signal after perturbation compensation;
• and
• connecting a feedback system between the gain error circuit and the variable gain amplifier, the feedback system being arranged to provide a gain control signal to the variable gain amplifier to reduce the magnitude of the gain error signal.

A method for processing optical signal signals output from a fiber optic gyroscope, comprising the steps of:

• arranging a perturbation injection circuit to provide a perturbation signal ±d;
• connecting a phase modulator between the perturbation injection circuit and the fiber optic gyro, the phase modulator being arranged to apply the perturbation to the fiber optic gyroscope;
• arranging a variable gain amplifier to receive the electrical signals indicative of optical signal signals output from the fiber optic gyroscope and provide an amplified signal;
• arranging a perturbation compensation circuit to apply perturbation compensation signals to signals output from the variable gain amplifier, the perturbation compensation circuit being arranged to provide a compensated signal by reducing the magnitude of the perturbation in the amplified signal output from the variable gain amplifier;
• connecting a gain error circuit to the perturbation compensation circuit, the gain error circuit being arranged to produce a gain error signal that indicates the magnitude of perturbation remaining in the amplified signal after perturbation compensation;
• connecting a feedback system between the gain error circuit and the variable gain amplifier, the feedback system being arranged to provide a gain control signal to the variable gain amplifier to reduce the magnitude of the gain error signal;
• and
• connecting processing circuitry between the perturbation compensation circuit and the phase modulator for determining the rotation rate sensed by the fiber optic gyroscope and for controlling the phase modulator to apply a rate nulling signal to the fiber optic gyroscope.