Patent
Linearized three state phase detector
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TLDR
In this article, a linearized three state phase detector (300) exhibits a linear transfer function of phase to current or charge at and around the zero phase error region, where inputs to the D flip-flops (301 and 302) are tied to a logic high.Abstract:
A linearized three state phase detector (300) that exhibits a linear transfer function of phase to current or charge at and around the zero phase error region. The inputs to the D flip-flops (301 and 302) are tied to a logic high. The first flip-flop (301) is clocked with reference signal F r while the other flip-flop (302) is clocked with a variable frequency feedback signal F v . F v is typically from a voltage controlled oscillator in a phase locked loop. The outputs of the flip-flops are ANDed together with the result of this operation going through a delay element (304) before reseting one of the flip-flops (301). The other flip-flop (302) is reset by the output of the AND gate (304) without the delay element (304). Each flip-flop output enables a charge pump - one negative polarity (306) and one positive polarity (305). The present invention (300) will maintain a lock condition in a phase locked loop by extending the DOWN pulse enabling the negative polarity charge pump (306) to the same width as the UP pulse that enables the positive pump (305). This will create a net zero charge from the present invention (300).read more
Citations
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References
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TL;DR: In this article, the phase and frequency comparator is used to eliminate non-linearities which would otherwise be inherent in its transfer function and thereby degrade performance of phase-locked systems employing the comparator.
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