Electrical computers and digital processing systems: support – Clock – pulse – or timing signal generation or analysis – Correction for skew – phase – or rate
Patent
1998-03-13
2000-06-27
Heckler, Thomas M.
Electrical computers and digital processing systems: support
Clock, pulse, or timing signal generation or analysis
Correction for skew, phase, or rate
327147, 331 25, G06F 104
Patent
active
060819057
ABSTRACT:
A PLL circuit for selecting a clock signal from among a plurality of clock signals having different phases is disclosed. The PLL circuit includes a selector for selecting at least one of the plurality of clock signals. Duty cycle distortion is avoided by ensuring that at least one of the clock signals is always selected to drive the output of the PLL circuit, P.sub.out. In one implementation, at least two of the clock signals are selected at a given time, so that at least one of the selected signals is always driving the output during a transition from one set of selected clock signals to another set of selected clock signals. In another implementation, the selector activates a desired clock signal before deactivating the currently selected clock signal, so that at least one of the clock signals is always selected. More than two phases can be simultaneously selected, for example, if there is a large capacitive load on the output signal, P.sub.out. The PLL circuit can be programmed to select only one clock phase at lower clock speeds.
REFERENCES:
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patent: 5574757 (1996-11-01), Ogawa
patent: 5646968 (1997-07-01), Kovacs et al.
patent: 5663687 (1997-09-01), Kozu
J. Sonntag & R.H. Leonowich, "A Monolithic CMOS 10MHz DPLL for Burstmode Data Retiming", pp. 194-195, International Solid-State Circuits Conference (1990).
Larsson Patrik
O'Neill Jay Henry
Heckler Thomas M.
Lucent Technologies - Inc.
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