“Pulse Insert”
Abstract
A noise reduction circuit useful as a clock restoration circuit includes a DC removal circuit for removing a DC level from an input pulse train. An integrator integrates the input pulse train after a DC level has been removed and a comparator compares the integrator output with a threshold value (Vmp) to detect for a missing pulse. A pulse generator inserts into the input pulse train an additional pulse delayed with respect to any missing pulse and an output pulse train having reduced noise is derived from the integrator output. In another noise reduction circuit blanking pulses are generated and are used to cancel additional spurious pulses in the input pulse train. A phase noise reduction circuit producing a pulse train having a predetermined phase relationship and/or duty cycle relative to an input signal or a clock signal is also described. Also described is the application of such circuits to a fractional rate multiplier circuit and a fractional-N phase-locked loop synthesiser.
Commentary
This patent principally addresses clock jitter suppression and ‘skew’ removal, which is a major bottleneck in large integrated circuits. It also teaches means for extracting and restoring a clock from a digital data stream that has no associated clock, or one having excessive jitter. The following are the four principal aspects of this invention:
- pulse doubler – this provides a means for inserting missing pulses, giving a clock restoration capability.
- pulse deleter – this allows the deletion of spurious pulses, which also helps with clock restoration.
- multiphase output, dual comparator / latch output – these have applicability in many digital systems incorporating multiphase clocks. The dual comparator / latch output is an alternative to the monostable output.
- fractional-n synthesiser – AJCs can be used to reduce noise in many sorts of synthesizer of which the most important is the fractional-n type.
PCT filing
Filed on 6th July 1998 as PCT application PCT/GB98/02001 with priority date 7th July 1997.