US 5,493,256 AGranted

Phase locked signal generator to produce a clock signal in phase with a trigger

AssigneeCanon Kabushiki Kaisha

InventorsSomei Kawasaki, Masami Iseki, Hironari Ebata

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Abstract

A phase-locked signal generator which performs phase-locked control of the output of a triangular-wave VCO when a trigger signal is not inputted, and which performs, when the trigger signal is inputted, short interval suspension of oscillation of the triangular-wave VCO, and detection of a phase difference between the trigger signal and the reference clock signal by a successive phase measuring portion after the short interval by using the triangular-wave signal, thereby obtaining phase data. The measured phase data is held until the next trigger signal, and the phase of the triangular-wave VCO is controlled in accordance with the phase data so that the triangular-wave signal has a fixed phase with respect to the reference clock signal. A square-wave signal outputted from the triangular-wave VCO is used as the phase-locked clock signal. This makes it possible to generate the phase-locked clock signal at higher stability than a conventional circuit, and to improve jitter without using the multiplied frequency of the phase-locked clock signal.

Claims13

Dependent claims

A phase-locked signal generator producing a phase-locked clock signal in phase with a trigger signal, comprising:

reference clock signal generating means for generating a reference clock signal having the same frequency as the phase-locked clock signal;
reset pulse generating means for generating a reset pulse in response to the trigger signal;
triangular-wave generating means for generating a triangular-wave signal, whose frequency is identical to that of the phase-locked clock signal, from a particular phase after a predetermined time has elapsed from the input of the trigger signal, said triangular-wave generating means suspending its oscillation for the predetermined time in response to the reset pulse;
phase detecting means for detecting a phase difference between the triangular-wave signal and the reference clock signal, and for holding the detected phase difference;
and
phase control means for controlling said triangular-wave generating means after the phase detection by said phase detecting means, so that the phase difference between the reference clock signal and the triangular-wave signal is maintained at the phase difference held by the phase detecting means,
wherein said phase detecting means comprises:
a first comparator comparing the triangular-wave signal with reference voltage, and outputting the comparison result in the form of a digital signal;
holding means for sequentially holding the digital signal outputted from said first comparator at a particular phase of the reference clock signal during a phase detecting period, and for outputting held digital signals as a digital reference voltage;
and
a D/A converter converting the digital reference voltage outputted from the holding means into an analog signal, and outputting the analog signal as the reference voltage,
wherein the reference voltage is controlled to successively approximate a voltage of the triangular-wave signal at the particular phase of the reference clock signal.

9 more elements

An apparatus for generating a clock signal whose phase is synchronized with a trigger signal, said apparatus comprising:

means for generating a reference clock signal;
means for generating a first clock signal whose frequency is variably controlled, and whose phase is in phase with said trigger signal;
phase detecting means for detecting a phase difference between the first clock signal and the reference clock signal in response to the trigger signal;
means for generating a second clock signal, a phase difference of said second clock signal from that of the first clock signal being variably set;
means for setting the phase difference of the second clock signal from the first clock signal in accordance with the phase difference detected by said phase detecting means;
and
means for comparing the phase of the second clock signal, with which the phase difference from said first clock signal is set, with the phase of the reference clock signal, and for controlling the frequency of the first clock signal.

4 more elements

Dependencies are inferred from the claim text.