Digital PLL circuit
AssigneeFujitsu Limited
InventorsSyouji Ohishi, Masaya Tamamura, Koichi Hatta
Life of this patent
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Abstract
A digital PLL circuit recovers a clock signal from an analog baseband signal. The PLL circuit has a phase comparator. The phase comparator provides a loop filter with a control value for a period of the recovered clock signal after a determination is made. If the determination is that the baseband signal has crossed a transition level, the control value corresponds to a time difference between a sampling point and a transition-level crossing point of the baseband signal. If the determination is that the baseband signal has not crossed the transition level, the control value is 0. The PLL circuit shortens a lockup time and provides stable operation even if the baseband signal involves an offset.
Claims4
A digital PLL circuit for recovering a clock signal from an analog baseband signal whose frequency band is limited due to removal of high-frequency components, having an A/D converter for sampling the baseband signal according to the recovered clock signal, a phase comparator for detecting a phase difference between the output of the A/D converter and the recovered clock signal, a loop filter for integrating the phase difference, and a voltage-controlled oscillator (VCO) for changing the oscillation frequency of itself in response to the output of the loop filter and providing the recovered clock signal, the phase comparator comprising:
- transition level crossing device for determining whether or not the base band signal has crossed a transition level;
- and
- control value providing device for providing the loop filter with a control value for a period of the recovered clock signal after said determination is made, the control value corresponding to a time difference between a sampling point and a transition-level crossing point of the baseband signal when the determination is that the baseband signal has crossed the transition level, and the control value corresponding to 0 when the determination is that the baseband signal has not crossed the transition level.
Dependencies are inferred from the claim text.