Phase locked loop
First Claim
1. A phase locked loop, comprising:
- reference oscillator means for generating a low phase noise reference frequency signal;
a voltage controlled oscillator for producing a desired output frequency signal;
a phase detector for comparing a phase of the low phase noise reference frequency signal to the desired output frequency signal; and
a loop filter for suppressing components of the low phase noise reference frequency signal;
wherein the reference oscillator means has a differential crystal oscillator circuit with a resonating crystal across differential outputs.
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Accused Products
Abstract
A periodic signal generation circuit includes a differential crystal oscillator suitable for integration on a semiconductor substrate. The oscillator utilizes an external crystal as a resonator. The circuit is designed such that differential sinusoidal signals are present on the resonator leads to provide superior noise rejection of interfering signals. Differential signal transmission is maintained throughout the oscillator to reject noise generated by other circuitry that may be present on the substrate. Noise radiated out from the oscillator through the power supply, substrate, bond wires and pads is reduced due to the generation of differential signals of controlled sinusoidal amplitude and low harmonic content. The oscillator produces low phase noise so that the oscillator may be used in applications, such as TV receivers, that are sensitive to distortion. The circuit is a square wave that has low jitter, thus reducing jitter produced in digital circuits that, would utilize this square wave clock signal.
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Citations
20 Claims
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1. A phase locked loop, comprising:
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reference oscillator means for generating a low phase noise reference frequency signal;
a voltage controlled oscillator for producing a desired output frequency signal;
a phase detector for comparing a phase of the low phase noise reference frequency signal to the desired output frequency signal; and
a loop filter for suppressing components of the low phase noise reference frequency signal;
wherein the reference oscillator means has a differential crystal oscillator circuit with a resonating crystal across differential outputs. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A phase locked loop, comprising:
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a reference oscillator configured to produce a differential low phase noise signal having a reference frequency;
a phase detector coupled to the reference oscillator;
a loop filter coupled to the phase detector; and
a voltage controlled oscillator coupled to the loop filter and configured to produce a signal having a desired frequency;
wherein the reference oscillator has a differential crystal oscillator circuit with a resonating crystal across differential outputs. - View Dependent Claims (16, 17)
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18. A phase locked loop, comprising:
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a reference oscillator configured to produce a differential low phase noise signal having a reference frequency;
a voltage controlled oscillator configured to produce a signal having a desired frequency;
a phase detector coupled between the reference oscillator and the voltage controlled oscillator; and
a loop filter coupled between the reference oscillator and the voltage controlled oscillator;
wherein the reference oscillator has a differential crystal oscillator circuit with a resonating crystal across differential outputs. - View Dependent Claims (19, 20)
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Specification