Phase comparator using digital and analogue phase detectors

DETAILED DESCRIPTION I claim: 1.
A phase detector comprising: a digital phase detector circuit responsive to a first signal having opposite edges, said circuit comprising: means for receiving a clock pulse signal, means for producing a reference signal synchronized with the clock pulse signal and having at least one edge, means responsive to said clock pulse signal for determining the number of clock pulses that occur in the time interval-between the time of occurrence of a given position between said opposite edges of said first signal and the time of occurrence of the at least one edge of said reference signal, and means responsive to said means49 providing a first digital output signal which represents said number of clock pulses; an analogue phase detector circuit comprising: means responsive to said first signal for producing a second signal having opposite edges which respectively correspond to the opposite edges of said first signal and is synchronized with said clock pulse signal, means for determining the time intervals between the corresponding edges of said first and second signals, means for determining a phase error voltage from the determined time intervals, and means for digitizing said phase error voltage to provide a second digital output signal; the phase detector further comprising means for combining said first and second digital output signals to produce a resultant digital output signal which represents an overall indication of phase difference.
2.
A phase detector as claimed in claim 1, where in said digital phase detector circuit comprises an up/down counter having an `enable ` input to which said first signal is to be applied, a `clock` input to which said clock pulse signal is to be applied, and an `up/down count` input to which a reference signal synchronised with said clock pulse signal is to be applied, together with output means operable for each occurrence of said first signal to output the count attained by said counter as said first digital output signal