Self-oscillating driver circuit for a quartz resonator of an angular rate sensor

• US 5,487,015 A
• Filed: 09/13/1993
• Issued: 01/23/1996
• Est. Priority Date: 09/13/1993
• Status: Expired due to Term

• Current Assignee: BEI Technologies, Incorporated
• Original Assignee: Rockwell International Corporation
• Inventors: White, Stanley A.
• Primary Examiner(s): Voeltz, Emanuel T.
• Assistant Examiner(s): Wachsman, Hal D.
• Application Number:
  US08/119,637
• Time in Patent Office: 862 Days
• Field of Search: 364/484, 364/481, 364/480, 73/504, 73/505, 73/517 A, 73/510, 73/1 E, 332/123, 332/124, 332/159, 332/160, 329/325, 324/658, 324/662, 331/105, 331/175, 333/235, 333/175, 361/244, 361/182, 361/184, 361/185, 361/203, 361/210, 361/146, 361/85, 361/76, 361/77
• US Class Current: 702/117
• CPC Class Codes: G01C 19/5607 using vibrating tuning forks double-ended tuning forks using planar vibrating masses suspended at opposite ends G01C19/5719

Abstract

A drive circuit provides approximately zero phase shift across the terminals of a resonator, and provides a constant excitation of the resonator, while cancelling variation due to the shunt capacitance. For complex demodulation of an angular rate signal from a vibrating quartz angular rate sensor, the drive circuit also provides an in-phase reference signal and a quadrature-phase reference signal. Preferably, the drive circuit includes an adjustable phase shifter connected in a feedback loop including the resonator for adjusting a phase shift of a periodic signal circulating in the feedback loop, and the adjustable phase shifter includes a Hilbert transformer for producing an in-phase signal and a quadrature-phase signal, and a combiner circuit connected to the Hilbert transformer for combining a selected amount of the quadrature signal with the in-phase signal to produce a result shifted by a selected amount of phase. The drive circuit also includes a phase detector responsive to phase shift across the resonator terminals for adjusting the phase shifter for obtaining a phase shift of approximately zero across the terminals. An automatic gain control is included in the feedback loop for obtaining a constant level of excitation of the resonator by the periodic signal. The feedback loop also has an adaptive circuit for canceling a component of the periodic signal passing through shunt capacitance of the resonator between the resonator terminals.

Claims

1. A method of exciting a resonator at a resonant frequency of said resonator, said resonator having a pair of terminals, said method comprising the steps of:

(a) generating a periodic signal by a feedback loop including said resonator;

(b) exciting said resonator with a periodic signal across said pair of terminals, said periodic signal having a frequency approximately equal to said resonant frequency;

(c) determining phase shift of said periodic signal across said pair of terminals; and

(d) adjusting said frequency of said periodic signal in response to said phase shift, by adjusting a phase shift of said periodic signal through said feedback loop, so that said phase shift is approximately zero, wherein said phase shift of said periodic signal through said feedback loop is adjusted by passing said periodic signal through a Hilbert transformer to produce an in-phase signal and a quadrature-phase signal, and combining a selected amount of said quadrature-phase signal with said in-phase signal to produce a result shifted by a selected amount (a) of phase, wherein said selected amount of said quadrature signal is combined with said in-phase signal by computing the sum of cos(a) times the in-phase signal and sin(a) times the quadrature-phase signal to produce said result that is shifted in phase by said selected amount (a) of phase.

2. A method of exciting a resonator at a resonant frequency of said resonator, said resonator having a pair of terminals, said method comprising the steps of:

(a) generating a periodic signal by a feedback loop including said resonator;

(b) exciting said resonator with a periodic signal across said pair of terminals, said periodic signal having a frequency approximately equal to said resonant frequency;

(c) determining, from phase shift of said periodic signal through a predetermined time delay, a phase shift of said periodic signal across said pair of terminals, said predetermined time delay being approximately a total delay of said periodic signal through a digital-to-analog converter, an analog-to-digital converter in series in said feedback loop, and an analog portion of said feedback loop situated between said digital-to-analog converter and said analog-to-digital converter; and

(d) adjusting said frequency of said periodic signal in response to said phase shift, by adjusting the phase shift of said periodic signal through said feedback loop, so that said phase shift of said periodic signal across said pair of terminals is approximately zero.

3. A drive circuit for exciting a resonator at a resonant frequency of said resonator, said resonator having a pair of terminals, said drive circuit comprising:

(a) an adjustable phase shifter connected in a feedback loop including said resonator for adjusting a phase shift of a periodic signal circulating in said feedback loop, said adjustable phase shifter including a Hilbert transformer for producing an in-phase signal and a quadrature-phase signal, and a combiner circuit connected to said Hilbert transformer for combining a selected amount of said quadrature-phase signal with said in-phase signal to produce a result shifted by a selected amount (a) of phase, wherein said combiner circuit includes a first multiplier connected to said Hilbert transformer for multiplying said in-phase signal by cos(a), a second multiplier connected to said Hilbert transformer for multiplying said quadrature-phase signal by sin(a), and a summing node connected to said first multiplier and said second multiplier for producing said result shifted by said selected amount (a) of phase; and

(b) a phase detector responsive to a phase shift across said pair of terminals and connected to said adjustable phase shifter for adjusting said adjustable phase shifter for obtaining a phase shift of said periodic signal of approximately zero across said pair of terminals.

4. A drive circuit for exciting a resonator at a resonant frequency of said resonator, said resonator having a pair of terminals, said drive circuit comprising:

(a) an adjustable phase shifter connected in a feedback loop including said resonator for adjusting a phase shift of a periodic signal circulating in said feedback loop; and

(b) a phase detector responsive to phase shift across said terminals and connected to said phase shifter for adjusting said phase shifter for obtaining a phase shift of said periodic signal of approximately zero across said terminals; and

(c) an adaptive circuit connected to said adjustable phase shifter and said phase detector for canceling a component of said periodic signal passing through shunt capacitance of said resonator between said terminals, wherein said adaptive circuit includes;

(1) a test oscillator connected in said feedback loop for exciting said resonator with a test signal;

(2) a multiplier connected to said adaptive circuit for generating a cancellation signal proportional to said periodic signal and a shunt capacitance estimating signal;

(3) a combiner connected in said feedback loop and connected to said multiplier for canceling said component of said periodic signal passing through said shunt capacitance of said resonator; and

(4) a shunt capacitance estimator connected to said combiner and said multiplier for adjusting said shunt capacitance estimating signal in order to minimize the presence of said test signal passing in said feedback loop from said combiner by the steps of;

(A) multiplying an estimate of the shunt capacitance by the test signal to produce a product signal;

(B) scaling and delaying the product signal to produce the cancellation signal;

(C) demodulating the combined signal by the test signal produce a residual;

(D) calculating the difference between;

(1) a scaled and delayed residual and

(2) the sum of a delayed residual and a double delayed residual;

(E) increasing the estimate of shunt capacitance if the difference is positive; and

(F) decreasing the estimate of shunt capacitance if the difference is negative.

5. The drive circuit as claimed in claim 4, further comprising an automatic gain control circuit connected to said adjustable phase shifter and said combiner in said feedback loop for adjusting the amplitude of said periodic signal to obtain a constant amplitude of said periodic signal passing from said combiner.

6. A drive circuit for exciting a resonator at a resonant frequency of said resonator having a pair of terminals, said drive circuit comprising:

(a) and adjustable phase shifter connected in a feedback loop including said resonator for adjusting a phase shift of a periodic signal circulating in said feedback loop, said adjustable phase shifter including;

(1) a Hilbert transformer for producing an in-phase signal and a quadrature-phase signal; and

(2) a combiner circuit connected to said Hilbert transformer for combining a selected amount of said quadrature-phase signal with said in-phase signal to produce a result shifted by a selected amount (α

) of phase, said combiner circuit including;

(A) a first multiplier connected to said Hilbert transformer for multiplying said in-phase signal by cos(α

);

(B) a second multiplier connected to said Hilbert transformer for multiplying said quadrature-phase signal by sin(α

); and

(C) a summing note connected to said first multiplier and said second multiplier for producing said result shifted by said selected amount (α

) of phase;

(b) a phase detector responsive to the phase shift across said pair of terminals and connected to said adjustable phase shifter for adjusting said adjustable phase shifter for obtaining a phase shift of said periodic signal of approximately zero across said pair of terminals;

(c) an automatic gain control connected to said adjustable phase shifter in said feedback loop for obtaining a constant level of excitation of said resonator by said periodic signal; and

(d) an adaptive circuit connected to said adjustable phase shifter and said phase detector for canceling a component of said periodic signal passing through the shunt capacitance of said resonator between said pair of terminals, said adaptive circuit including;

(1) a test oscillator connected in said feedback loop for exciting said resonator with a test signal;

(2) a multiplier having a first input which is connected to said adaptive circuit for generating a cancellation signal proportional to said periodic signal and a shunt capacitance estimating signal;

(3) a combiner connected in said feedback loop and connected to an output of said cancellation-signal-generating multiplier for canceling said component of said periodic signal passing through said shunt capacitance of said resonator; and

(4) a shunt capacitance estimator connected to an output of said combiner and to a second input of said cancellation-signal-generating multiplier for adjusting said shunt capacitance estimating signal in order to minimize the presence of said test signal passing in said feedback loop from said combiner by the steps of;

(A) multiplying, in said cancellation-signal-generating multiplier, an estimate of the shunt capacitance by the test signal to produce a product signal;

(B) scaling and delaying the product signal to produce the cancellation signal applied to said combiner;

(C) demodulating, in said shunt capacitance estimator, the combined signal by the test signal to produce a residual;

(D) calculating, in said shut capacitance estimator, the difference between;

(1) a scaled and delayed residual and

(2) the sum of a delayed residual and a double delayed residual;

(E) increasing, in said shut capacitance estimator, the estimate of shunt capacitance if the difference is positive; and

(F) decreasing, in said estimator, the estimate of shunt capacitance if the difference is negative.