Damping decoupled oscillator using a high impedance crystal
First Claim
1. A damping decoupled crystal oscillator comprising:
- (a) a piezoelectric crystal driven to oscillate close to its resonant frequency, producing a periodic signal, the piezoelectric crystal being connected to a feedback loop providing a feedback signal derived from the periodic signal, to sustain oscillation of the piezoelectric crystal;
(b) a variable gain amplifier connected to amplify the periodic signal produced by the piezoelectric crystal at a gain dependent upon a gain control signal;
(c) variable phase shift means, connected in series relationship with the variable gain amplifier, for introducing a phase shift in the signal produced by the piezoelectric crystal in response to a phase control signal, the series connected variable gain amplifier and phase shift means producing an output signal comprising the feedback signal;
(d) level detecting means connected to receive the output signal and operative to determine the amplitude of the output signal to produce the gain control signal;
(e) damping change compensation means, connected to receive the gain control signal, for producing the phase control signal as a function of the gain control signal, the frequency of said output signal being thus compensated for and decoupled from changes in damping to which the piezoelectric crystal may be subjected.
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Abstract
A crystal controlled oscillator in which changes in damping are compensated and a method for decoupling the output signal of such an oscillator from damping changes. The damping decoupled oscillator includes a quartz crystal (10), which produces a periodic signal, connected in series with a variable gain amplifier (18) and a variable phase shift circuit (22). Feedback from the output of the variable phase shift circuit is provided to sustain oscillation of the crystal. Unity gain in the loop is maintained by adjusting the gain of the variable gain amplifier in accordance with the DC value of the output signal, provided by a precision rectifier (34). As the DC value of the output signal changes due to changes in damping or energy loss of the crystal, an absolute value circuit (38) responds by providing a phase control signal for adjusting the phase of the periodic signal to compensate for changes in damping. The output signal of the oscillator is thus controlled at a constant amplitude, with substantially reduced frequency shift.
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Citations
18 Claims
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1. A damping decoupled crystal oscillator comprising:
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(a) a piezoelectric crystal driven to oscillate close to its resonant frequency, producing a periodic signal, the piezoelectric crystal being connected to a feedback loop providing a feedback signal derived from the periodic signal, to sustain oscillation of the piezoelectric crystal; (b) a variable gain amplifier connected to amplify the periodic signal produced by the piezoelectric crystal at a gain dependent upon a gain control signal; (c) variable phase shift means, connected in series relationship with the variable gain amplifier, for introducing a phase shift in the signal produced by the piezoelectric crystal in response to a phase control signal, the series connected variable gain amplifier and phase shift means producing an output signal comprising the feedback signal; (d) level detecting means connected to receive the output signal and operative to determine the amplitude of the output signal to produce the gain control signal; (e) damping change compensation means, connected to receive the gain control signal, for producing the phase control signal as a function of the gain control signal, the frequency of said output signal being thus compensated for and decoupled from changes in damping to which the piezoelectric crystal may be subjected. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for compensating for changes in damping of a crystal oscillator comprising the steps of
(a) determining the amplitude of an output signal derived from a periodic signal produced by the oscillator to provide a gain control signal; -
(b) amplifying the periodic signal of the oscillator with a gain that is a function of the gain control signal; and (c) varying the phase of the periodic signal as a function of the gain control signal to decouple and compensate for changes in damping to which the crystal may be subjected. - View Dependent Claims (8, 9, 10, 11, 12)
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13. Apparatus for compensating a periodic signal output from a crystal oscillator for changes in damping, comprising:
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(a) a variable gain amplifier having a voltage controlled gain, the variable gain amplifier being connected to amplify the periodic signal output from the oscillator; (b) a variable phase shifting means, connected in series with the variable gain amplifier, for shifting the phase of the periodic signal in response to a phase control signal, the variable phase shifting means and the variable gain amplifier together producing an output signal; (c) a rectifier connected to rectify the output signal and to produce a DC voltage corresponding thereto;
the DC voltage being input to the variable gain amplifier to control its gain; and(d) damping compensation means for producing the phase control signal as a function of the DC voltage produced by the rectifier, the phase control signal causing the variable phase shifting means to vary the phase of the periodic signal to compensate for changes in the oscillator damping. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification