Low-noise high-stability crystal oscillator
First Claim
1. An integrated circuit comprising:
- a gain element configured to drive a crystal;
a DC control loop configured to adjust a DC level of a signal at an output of the gain element; and
an amplitude control loop configured to adjust an amplitude of the signal at the output of the gain element,wherein the DC control loop comprises an amplifier in communication with the gain element, the amplifier separate from the amplitude control loop.
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Accused Products
Abstract
Circuits, methods, and apparatus that provide low-noise, high-stability crystal oscillators having controlled-amplitude differential output signals and DC level control. A crystal oscillator circuit has two feedback loops, one for setting the DC level of its signals, the other for adjusting the amplitude of those signals. The DC level feedback loop can set the DC component of the oscillator signals to a voltage midway between two supply voltages. The amplitude control loop sets the amplitude of the output of the crystal oscillator signal to be within a range. The amplitude can be set to provide a maximum swing without clipping the supply voltages in order to provide high-stability and minimal jitter. The amplitude control circuit can also be digital for improved noise performance. The time constants of these two loops can be separated such that instabilities are avoided.
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Citations
34 Claims
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1. An integrated circuit comprising:
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a gain element configured to drive a crystal; a DC control loop configured to adjust a DC level of a signal at an output of the gain element; and an amplitude control loop configured to adjust an amplitude of the signal at the output of the gain element, wherein the DC control loop comprises an amplifier in communication with the gain element, the amplifier separate from the amplitude control loop. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 16)
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11. An integrated circuit comprising:
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a gain element configured to drive a crystal; a DC control loop configured to adjust a DC level of a signal at an output of the gain element; and an amplitude control loop configured to adjust an amplitude of the signal at the output of the gain element, wherein the amplitude control loop comprises an amplitude measurement circuit configured to provide a measurement of an amplitude of the signal at the input of the gain element and a comparator configured to compare the measurement of the amplitude of the signal at the input of the gain element with a high threshold and a low threshold, the comparator further configured to provide one or more signals in response to the comparisons. - View Dependent Claims (12, 13, 14)
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17. A method of generating a first oscillator signal comprising:
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driving a resonant element to generate a first oscillator signal; adjusting a DC level of the first oscillator signal; and adjusting an amplitude of the first oscillator signal, wherein adjusting the DC level comprises using an amplifier separate from a control loop for adjusting the amplitude of the first oscillator signal. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 31, 32)
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27. A method of generating a first oscillator signal comprising:
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driving a resonant element to generate a first oscillator signal; adjusting a DC level of the first oscillator signal; and adjusting an amplitude of the first oscillator signal by; measuring an amplitude of a second oscillator signal; providing a measurement of the amplitude of the second oscillator signal; comparing the measurement of the amplitude of the second oscillator signal with a high threshold and a low threshold; and providing one or more signals in response to the comparison. - View Dependent Claims (28, 29, 30)
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33. An integrated circuit comprising:
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a gain element configured to drive a resonant element; a DC control loop configured to adjust a DC level of a signal at an output of the gain element; and an amplitude control loop configured to adjust an amplitude of the signal at the output of the gain element, wherein the DC control loop comprises an amplifier in communication with the gain element, the amplifier separate from the amplitude control loop. - View Dependent Claims (34)
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Specification