Frequency and phase-locked two-phase digital synthesizer
First Claim
1. A digital oscillator including an in-phase delay unit and a quadrature delay unit connected in a feedback circuit, said digital oscillator including a roundoff compensation system for computing a corrected value for an output of each delay unit based on a value of a filtered output of the other delay unit when the value of the filtered output of said other delay unit is within predetermined limits, the digital oscillator being of the two phase, that is, in-phase and quadrature phase, state variable type, with at least four multipliers, the roundoff compensation system comprising:
- (a) means for eliminating the accumulation of roundoff error, such means comprising means for causing, when a magnitude of an output value of either phase is below a predetermined threshold, the output value of the other phase to be computed by a Chebyshev approximation;
(b) means for driving two of the four multipliers directly by a control input, x, and the other two multipliers by a Chebyshev approximation to (1-x2).sup. 1/2 ; and
(c) a pair of filters for reducing any noise generated by element (a), namely, an in-phase filter placed between the in-phase delay unit output and an in-phase roundoff compensation unit output, and a quadrature filter placed between the quadrature delay unit output and an quadrature roundoff compensation unit output, the coefficients for the filters being supplied under the direction of the control input x.
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Accused Products
Abstract
For use with a quartz angular rate sensor, a frequency and phase-locked synthesizer recovers a reference signal virtually free of phase noise, and generates a quadrature-phase reference signal for complex demodulation of the angular rate signal. The synthesizer also ensures a precisely adjusted phase shift of approximately zero across the drive tines of the sensor. Moreover, the digital synthesizer provides a precise numerical indication of the drive frequency, which can be used for compensation and automatic tuning of filters, such as a tracking filter, a filter in an automatic gain control, and notch filters in the phase and/or frequency detectors in the digital synthesizer. The tracking filter is used as a pre-filter for the synthesizer, and is responsive to a passband-width control signal generated from the magnitude of the frequency and phase error signal controlling the frequency generated by the synthesizer. Preferably the synthesizer has an oscillator controller for producing a pair of frequency control signals that are the sine and cosine of a frequency control parameter (φ), and one of these control signals is generated from the other by a polynomial approximation. To compensate for roundoff error, when one of the in-phase or quadrature-phase outputs has a magnitude less than a limit value, a compensated value for the other output is computed from an even polynomial of the magnitude.
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Citations
17 Claims
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1. A digital oscillator including an in-phase delay unit and a quadrature delay unit connected in a feedback circuit, said digital oscillator including a roundoff compensation system for computing a corrected value for an output of each delay unit based on a value of a filtered output of the other delay unit when the value of the filtered output of said other delay unit is within predetermined limits, the digital oscillator being of the two phase, that is, in-phase and quadrature phase, state variable type, with at least four multipliers, the roundoff compensation system comprising:
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(a) means for eliminating the accumulation of roundoff error, such means comprising means for causing, when a magnitude of an output value of either phase is below a predetermined threshold, the output value of the other phase to be computed by a Chebyshev approximation; (b) means for driving two of the four multipliers directly by a control input, x, and the other two multipliers by a Chebyshev approximation to (1-x2).sup. 1/2 ; and (c) a pair of filters for reducing any noise generated by element (a), namely, an in-phase filter placed between the in-phase delay unit output and an in-phase roundoff compensation unit output, and a quadrature filter placed between the quadrature delay unit output and an quadrature roundoff compensation unit output, the coefficients for the filters being supplied under the direction of the control input x. - View Dependent Claims (2)
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3. A digital sinusoidal synthesizer comprising:
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(a) a digital oscillator including an in-phase delay unit and a quadrature delay unit connected in a feedback circuit, said digital oscillator including a roundoff compensation system for computing a corrected value for an output of each delay unit based on a value of a filtered output of the other delay unit When the value of the filtered output of said other delay unit is within predetermined limits, the digital oscillator being of the two phase, that is, in-phase and quadrature phase, state variable type, with at least four multipliers, the roundoff compensation system comprising; (1) means for eliminating the accumulation of roundoff error, such means comprising means for causing, when a magnitude of an output value of either phase is below a predetermined threshold, the output value of the other phase to be computed by a Chebyshev approximation; (2) means for driving two of the four multipliers directly by a control input, x, and the other two multipliers by a Chebyshev approximation to (1-x2).sup. 1/2 ; and (3) a pair of filters for reducing any noise generated by element (a), namely, an in-phase filter placed between the in-phase delay unit output and an in-phase roundoff compensation unit output, and a quadrature filter placed between the quadrature delay unit output and a quadrature roundoff compensation unit output, the coefficients for the filters being supplied under the direction of the control input x; (b) a discriminator having a reference input; (c) a controller including a first accumulator, a saturating element, and a scaling multiplier, connected to take signals from the discriminator and pass them to the oscillator; and (d) a feedback loop, including a filter whose parameters are set by the oscillator, from the output of the oscillator to the reference input of the discriminator. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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Specification