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US 6,636,122 B2Granted
Analog frequency locked loop with digital oversampling feedback control and filter
AssigneeZilog, Inc.
InventorAnatoliy V. Tsyrganovich
Life of this patent
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Abstract
A filter using analog to digital conversion, digital filtering and oversampling noise reshaping is disclosed. Application of such a filter to a frequency locked oscillator is disclosed. Application of such a filter to an oscillator having a capability to synchronize with an external stimulus is disclosed.
Claims19
A feedback comprising:
- at least one ramp generator for generating a first ramp-like signal in response to a first edge of a first input pulse signal having a first duration, the at least one ramp generator further generating a second ramp-like signal in response to a second edge of the first input pulse signal;
- a clocked analog to digital converter circuit located downstream of the ramp generator and being actuated by a first edge of a second input signal having a second duration to produce a first digital sample, the clocked analog to digital converter circuit further being actuated by a second edge of the second input pulse signal to produce a second digital sample;
- a conversion circuit for generating a digital correction signal by differencing the first digital sample from the second digital sample wherein the digital correction signal represents a difference between the first duration and the second duration;
- and
- a digital low pass filter for filtering the digital correction signal to produce a filtered correction signal.
2 more elements
A synchronized oscillator comprising:
- a reference clock input adapted to receive a reference clock signal;
- a synchronizing signal input adapted to receive a synchronizing edge;
- a voltage-controlled oscillator for generating an output clock signal at an output clock frequency, the voltage-controlled oscillator resetting in response to the synchronizing edge, the voltage-controlled oscillator having a correction input to receive a correction signal for controlling the output clock frequency;
- and
- a feedback circuit adapted to receive the output clock signal and the reference clock signal, the feedback circuit generating the correction signal,
- wherein the correction signal is generated by the acts of:
- a) digitizing a first difference between leading edges of a first pulse having a first duration in proportion to frequency of the output clock signal and of a second pulse having a second duration in proportion to a frequency of the reference clock,
- b) digitizing a second difference between trailing edges of the first pulse and the second pulse,
- c) differencing the first difference and the second difference to produce a third difference, and
- d) performing digital to analog conversion upon a signal derived from the third difference.
7 more elements
A method for generating a feedback signal comprising the acts of:
- a) digitizing a first difference between leading edges of a first pulse having a first duration in proportion to a frequency of an output clock signal and of a second pulse having a second duration in proportion to a frequency of a reference clock,
- b) digitizing a second difference between trailing edges of the first pulse and the second pulse,
- c) differencing the first difference and the second difference to produce a third difference, and
- d) performing digital to analog conversion upon a signal derived from the third difference.
1 more element
A filter comprising:
- an analog to digital converter adapted to receive an input analog signal and further adapted to generate a corresponding unfiltered digital signal;
- a digital filter adapted to receive the unfiltered digital signal and further adapted to produce a corresponding filtered digital signal;
- an oversampling modulator adapted to receive the filtered digital signal and further adapted to produce a corresponding modulated digital signal wherein the modulated digital signal has lower precision than the filtered digital signal;
- a digital to analog converter adapted to receive the modulated digital signal and further adapted to produce a corresponding filtered analog signal;
- and
- an analog low pass filter adapted to receive the filtered analog signal and further adapted to produce a corresponding smoothed analog signal.
3 more elements
Dependencies are inferred from the claim text.