Dual loop phase locked circuit with sweep generator and compensation for drift
AssigneeUnisys Corporation
InventorsRoy E. Greeff, Bruce H. Williams, Mark B. Falslev
Life of this patent
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Abstract
A dual loop phase locked circuit is disclosed in which a first loop includes a phase detector, a filter, and a VCO; as a second loop includes a sweep voltage generator, a compensation circuit, and the filter of the first loop. Due to the compensation circuit, the VCO accurately tracks a signal from the sweep voltage generator, even though the filter has an electrical parameter that drifts with time and/or age and/or component selection.
Claims10
A dual loop phase locked circuit comprising a first loop which includes a phase detector having an input for receiving an external signal, a filter having an input connected to receive an error signal from said phase detector, and a VCO having an input connected to receive a control voltage from said filter plus an output connected to another input of said phase detector;
- and a second loop which includes:
- a sweep voltage generator which generates an analog sweep voltage, separate from said control voltage, for said VCO to track;
- A compensation circuit having one input connected to receive said sweep voltage, having another input connected to receive said control voltage, and having a feedback coupling that sends a feedback current to a node in said filter which increases said control voltage as said analog current increases, and vice-versa;
- said filter including a non-ideal circuit component with a parameter that drifts and thereby produces variations in said control voltage;
- and,
- said compensation circuit including a comparator which neutralizes said variations by increasing said feedback current if said control voltage is less than said sweep voltage, and decreasing said feedback current if said control voltage is more than said sweep voltage.
Dependencies are inferred from the claim text.