US 5,331,342 A · Video clock generating circuit and horizontal synchronizing signal generating device in image forming apparatus using laser beam

Abstract

A basic clock generated from a crystal oscillator is delayed by a constant time in each of a plurality of delay elements connected in series. Consequently, internal clocks which differ in phase by a predetermined amount are outputted from the delay elements. Output signals of the delay elements are inputted to a clock selector. The clock selector selects any one of the internal clocks on the basis of a beam detection signal indicating the timing of the scanning of a photoreceptor by a laser beam to output the same as a video clock. The clock selector selects any one internal clock whose phase difference from the beam detection signal is closest to a predetermined phase difference out of the internal clocks, the phase difference from the beam detection signal meaning the time difference between the time when the beam detection signal has a predetermined phase angle and the time when the internal clock has a predetermined phase angle. A horizontal synchronizing signal is generated by counting a video clock at the timing based on the beam detection signal. The video clock outputted from the clock selector is synchronized with the beam detection signal with high precision. As a result, the horizontal synchronizing signal generated can be synchronized with the beam detection signal with high precision.

Claims12

Dependent claims

A video clock generating circuit for generating a video clock for defining a data processing operation for each pixel in an image forming apparatus which uses a laser beam, said circuit comprising:

beam detection signal generating means for generating a beam detection signal corresponding to the timing of laser beam scanning;
reference frequency signal generating means for generating a reference frequency signal;
a plurality of phase shifting means for shifting the phase of the reference frequency signal from the reference frequency signal generating means to generate a plurality of output signals which differ in phase by a predetermined amount;
a plurality of inverting means for respectively inverting output signals from the plurality of phase shifting means to provide a plurality of inverted output signals,
selecting means receiving respective output signals of the plurality of phase shifting means and the plurality of inverting means for selecting any one output signal whose phase difference from said beam detection signal is closest to a predetermined phase difference from among the output signals of said plurality of phase shifting means and said plurality of inverting means, the phase difference from the beam detection signal being the time difference between the time when the beam detection signal has a predetermined phase angle and the time when the respective output signals of the phase shifting means and the inverting means have a predetermined phase angle, to output the selected output signal as a video clock.

2 more elements

A horizontal synchronizing signal generating device for generating a horizontal synchronizing signal for synchronizing laser beam scanning and image data processing in an image forming apparatus using a laser beam, said device comprising:

beam detection signal generating means for generating a beam detection signal corresponding to the timing of laser beam scanning:
reference frequency signal generating means for generating a reference frequency signal;
a plurality of phase shifting means for shifting the phase of the reference frequency signal from the reference frequency signal generating means to generate a plurality of output signals which differ in phase by a predetermined amount;
selecting means receiving respective output signals of the plurality of phase shifting means for selecting any one output signal whose phase difference from said beam detection signal is closest to a predetermined phase difference from amount the output signals of the plurality of phase shifting means, the phase difference from the beam detection signal being the time difference between the time when the beam detection signal has a predetermined phase angle and the time when the output signal of the phase shifting means has a predetermined phase angle, to output the selected output signal as a video clock;
a horizontal synchronizing signal generating circuit receiving said beam detection signal and the video clock from said selecting means for generating a horizontal synchronizing signal which is synchronized with said beam detection signal by counting said video clock on the basis of said beam detection signal;
and
clock control means for preventing said video clock from being inputted to said horizontal synchronizing signal generating circuit in a time period immediately before and after selecting the signal to be the video clock in said selecting means.

4 more elements

beam detection signal generating means for generating a beam detection signal corresponding to the timing of laser beam scanning;
reference frequency signal generating means for generating a reference frequency signal;
a plurality of phase shifting means for shifting the phase of the reference frequency signal from the reference frequency signal generating means to generate a plurality of output signals which differ in phase by a predetermined amount;
a plurality of inverting means for respectively inverting the output signals of the plurality of phase shifting means to provide inverted output signals;
selecting means receiving respective output signals of the plurality of phase shifting means and the plurality of inverting means for selecting any one output signal whose phase difference from said beam detection signal is closest to a predetermined phase difference from among the output signals of the plurality of phase shifting means and the plurality of inverting means, the phase difference from the beam detection signal being the time difference between the time when the beam detection signal has a predetermined phase angle and the time when the output signal of the respective output signals of the phase shifting means and the inverting means have a predetermined phase angle, to output the selected output signal as a video clock;
and
a horizontal synchronizing signal generating circuit receiving said beam detection signal and the video clock from said selecting means for generating a horizontal synchronizing signal which is synchronized with said beam detection signal by counting said video clock on the basis of said beam detection signal.

4 more elements

Dependencies are inferred from the claim text.

Video clock generating circuit and horizontal synchronizing signal generating device in image forming apparatus using laser beam

Life of this patent

Video clock generating circuit and horizontal synchronizing signal generating device in image forming apparatus using laser beam

Life of this patent

Abstract

Claims12