Reducing metastable-induced errors from a frequency detector that is used in a phase-locked loop
AssigneeAgilent Technologies, Inc.
InventorThomas A. Knotts
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Abstract
A technique for reducing the likelihood that a frequency detector will incorrectly assert control over a VCO because of metastable-induced errors involves qualifying frequency detector control signals by requiring multiple consecutive control signals that indicate the frequency detector should assert control over the VCO before the frequency detector is allowed to assert control over the VCO. In an embodiment, the frequency detector control signals are qualified by a series of full-swing library cell flip-flops.
Claims20
A method for operating a phase-locked loop that includes a frequency detector, the method comprising:
- measuring the frequency of a voltage controlled oscillator (VCO) signal;
- determining whether the frequency detector should assert control over the VCO signal in response to the frequency measurement;
- qualifying the determination before the frequency detector is allowed to assert control over the VCO signal.
A frequency detector for use in a phase-locked loop, the frequency detector comprising:
- a counter for measuring the frequency of a signal from a voltage controlled oscillator (VCO) over a known sampling interval;
- an error detector, in signal communication with the counter, configured to determine if the frequency detector should assert control over the VCO in response to a frequency measurement from the counter;
- and
- a qualifier unit, in signal communication with the error detector, configured to qualify the determination that is made by the error detector before the frequency detector is allowed to assert control over the VCO.
A frequency detector for use in a phase-locked loop, the frequency detector comprising:
- a controller configured to receive a reference clock signal and to generate a counter enable signal;
- a synchronizer configured to receive a voltage controlled oscillator (VCO) signal and the counter enable signal and to generate a synchronized counter enable signal;
- a counter operating in response to the synchronized counter enable signal to measure the frequency the VCO signal over a known sampling interval;
- an error detector, in signal communication with the counter, configured to determine whether the frequency detector should assert control over the VCO in response to a frequency measurement from the counter;
- and
- a qualifier unit, in signal communication with the error detector, configured to qualify the determination made by the error detector before the frequency detector is allowed to assert control over the VCO.
Dependencies are inferred from the claim text.