Integrated, digitally-controlled crystal oscillator
First Claim
1. A variable frequency oscillator circuit, comprising:
- a resonant component;
a sustaining amplifier connected to said resonant component and generating an output signal, a first feedback loop connected to said sustaining amplifier for an in-phase component of said output signal, said first feedback loop including a limiter having an output amplitude signal that is substantially independent of its input amplitude signal; and
a second feedback loop connected to said sustaining amplifier for a quadrature signal component of said output signal bypassing said limiter, wherein the output frequency of said oscillator circuit is varied by altering said quadrature signal component.
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Abstract
A quartz crystal oscillator comprises a balanced circuit with a quartz crystal resonator device connected in series resonance across a balanced, low-impedance node within a sustaining amplifier. A phase modulator such as a quadrature modulator is included in the feedback loop to allow programming of the loop phase shift thereby to alter the frequency point on the crystal resonance curve at which the circuit oscillates. The in-phase loop signal is hardlimited while the quadrature loop signal component is not hardlimited with the effect that the frequency control curve slope is more accurately defined. An active neutralization of the crystal'"'"'s parasitic shunt capacitance is disclosed for obtaining a linear frequency control curve.
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Citations
33 Claims
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1. A variable frequency oscillator circuit, comprising:
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a resonant component;
a sustaining amplifier connected to said resonant component and generating an output signal, a first feedback loop connected to said sustaining amplifier for an in-phase component of said output signal, said first feedback loop including a limiter having an output amplitude signal that is substantially independent of its input amplitude signal; and
a second feedback loop connected to said sustaining amplifier for a quadrature signal component of said output signal bypassing said limiter, wherein the output frequency of said oscillator circuit is varied by altering said quadrature signal component. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A variable frequency oscillator circuit, comprising:
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a balanced, sustaining amplifier having differential inputs and outputs;
a crystal oscillator connected across said balanced, sustaining amplifier; and
a feedback loop comprising a first balanced phase shift component having a differential input connected to said balanced, sustaining amplifier differential output, and a differential output;
a balanced phase shifter having a differential input connected to said first balanced phase shift component differential output, a control input operative to alter the amount of phase shift, and a differential output;
a balanced limiter having a differential input connected to said balanced phase shifter differential output, and a differential output whose signal amplitude is substantially independent of the signal amplitude of its differential input; and
a second balanced phase shift component having a differential input connected to said balanced limiter differential output, and a differential output connected to said balanced, sustaining amplifier differential input; and
a control signal connected to said balanced phase shifter control input, whereby the output frequency of said variable frequency oscillator circuit varies in response to said control signal. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32)
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33. A variable frequency oscillator circuit having shunt capacitance neutralization, comprising:
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a balanced amplifier having differential inputs and outputs, comprising a first pair of transistors, each transistor having a gate, a collector, and an emitter, said differential inputs connected to the gates of said transistors and said differential outputs comprising the collectors of said transistors;
a crystal oscillator having a shunt capacitance connected between the emitters of said balanced amplifier transistors;
a second pair of transistors, each transistor having a gate, a collector, and an emitter, the collectors of said second pair of transistors cross-connected to the collectors of said first pair of transistors; and
a neutralizing capacitor connected between the emitters of said second pair of transistors, whereby current flow through said first pair of transistors due to the shunt capacitance of said crystal oscillator is cancelled by current flow through said second pair of transistors due to said neutralizing capacitor.
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Specification