Pixel clock generation apparatus, pixel clock generation method, and image forming apparatus capable of correcting main scan dot position shift with a high degree of accuracy

A pixel clock generation apparatus, comprising:

• a detecting circuit detecting a time interval between each two adjacent horizontal synchronization signals among three or more of the horizontal synchronization signals;
• a comparing part comparing each time interval detected by said detecting circuit with a target value and outputting each difference therebetween;
• a phase shift data generation part having at least one lookup table storing a pattern of phase shift data for controlling a phase shift amount of a pixel clock, and reading and outputting the phase shift data from the lookup table based on each difference that is output from said comparing part;
• a high frequency clock generation part generating a high frequency clock;
• and
• a pixel clock generation part generating a pixel clock whose phase is controlled in accordance with the phase shift data that are output from said phase shift data generating part based on the high frequency clock that is generated by said high frequency clock generating part.

A pixel clock generation method, comprising the steps of:

• detecting a time interval between two horizontal synchronization signals;
• reading phase shift data from a lookup table based on a difference between the detected time interval and a target value;
• and
• controlling phase of a pixel clock in accordance with the phase shift data.

A pixel clock generation method, comprising the steps of:

• detecting a time interval between each two adjacent horizontal synchronization signals among three or more of the horizontal synchronization signals;
• reading phase shift data from a lookup table based on each difference between the detected time interval and a target value;
• and
• controlling phase of a pixel clock in accordance with the phase shift data.

An image forming apparatus, comprising:

• a medium to be scanned;
• a light beam source outputting a light beam;
• a deflecting part deflecting the light beam output from said light beam source so that the deflected light beam scans said medium to be scanned and forms an image on said medium to be scanned;
• a pixel clock generation apparatus generating a pixel clock;
• and
• a horizontal synchronization detector detecting scan timings at which the light beam scans two or more specific horizontal scan positions, so as to generate two or more horizontal synchronization signals supplied to said pixel clock generation apparatus,
• said pixel clock generation apparatus including:
• a detecting circuit detecting a time interval between two of the horizontal synchronization signals;
• a comparing part comparing the time interval detected by said detecting circuit and a target value, and outputting a difference therebetween;
• a phase shift data generation part having a lookup table storing a pattern of phase shift data for controlling a phase shift amount of the pixel clock, and reading and outputting the phase shift data from the lookup table based on the difference that is output from said comparing part;
• a high frequency clock generation part generating a high frequency clock;
• and
• a pixel clock generation part generating the pixel clock whose phase is controlled in accordance with the phase shift data that are output from said phase shift data generating part based on the high frequency clock that is generated by said high frequency clock generating part,
• wherein said light beam source is driven in synchronization with the pixel clock generated by said pixel clock generation apparatus.

An image forming apparatus, comprising:

• a medium to be scanned;
• a light beam source outputting a light beam;
• a deflecting part deflecting the light beam output from said light beam source so that the deflected light beam scans said medium to be scanned and forms an image on said medium to be scanned;
• a pixel clock generation apparatus generating a pixel clock;
• and
• a horizontal synchronization detector detecting scan timings at which the light beam scans two or more specific horizontal scan positions, so as to generate two or more horizontal synchronization signals supplied to said pixel clock generation apparatus,
• said pixel clock generation apparatus including:
• a detecting circuit detecting a time interval between each two adjacent horizontal synchronization signals among three or more of the horizontal synchronization signals;
• a comparing part comparing each time interval detected by said detecting circuit with a target value and outputting each difference therebetween;
• a phase shift data generation part having one or more lookup tables each storing a pattern of phase shift data for controlling a phase shift amount of a pixel clock, and reading and outputting the phase shift data from one of the lookups table based on each difference that is output from said comparing part;
• a high frequency clock generation part generating a high frequency clock;
• and
• a pixel clock generation part generating a pixel clock whose phase is controlled in accordance with the phase shift data that are output from said phase shift data generating part based on the high frequency clock that is generated by said high frequency clock generating part,
• wherein said light beam source is driven in synchronization with the pixel clock generated by said pixel clock generation apparatus.

A tandem-type image forming apparatus, comprising:

• a plurality of color stations corresponding to respective colors, each including a light beam source for image writing, a pixel clock generation apparatus, and a horizontal synchronization detector for generating two or more horizontal synchronization signals supplied to said pixel clock generation apparatus,
• said pixel clock generation apparatus including:
• a detecting circuit detecting a time interval between two of the horizontal synchronization signals;
• a comparing part comparing the time interval detected by said detecting circuit and a target value, and outputting a difference therebetween;
• a phase shift data generation part having a lookup table storing a pattern of phase shift data for controlling a phase shift amount of a pixel clock, and reading and outputting the phase shift data from the lookup table based on the difference that is output from said comparing part;
• a high frequency clock generation part generating a high frequency clock;
• and
• a pixel clock generation part generating the pixel clock whose phase is controlled in accordance with the phase shift data that are output from said phase shift data generating part based on the high frequency clock that is generated by said high frequency clock generating part,
• wherein, in each of the color stations, said light beam source for image writing is driven in synchronization with the pixel clock generated by the pixel clock generation apparatus corresponding to the color station.

A tandem-type image forming apparatus, comprising:

• a plurality of color stations corresponding to respective colors, each including a light beam source for image writing, a pixel clock generation apparatus, and a horizontal synchronization detector for generating two or more horizontal synchronization signals supplied to said pixel clock generation apparatus,
• said pixel clock generation apparatus including:
• a detecting circuit detecting a time interval between each two adjacent horizontal synchronization signals among three or more of the horizontal synchronization signals;
• a comparing part comparing each time interval detected by said detecting circuit with a target value and outputting each difference therebetween;
• a phase shift data generation part having one or more lookup tables each storing a pattern of phase shift data for controlling a phase shift amount of a pixel clock, and reading and outputting the phase shift data from one of the lookup tables based on each difference that is output from said comparing part;
• a high frequency clock generation part generating a high frequency clock;
• and
• a pixel clock generation part generating a pixel clock whose phase is controlled in accordance with the phase shift data that are output from said phase shift data generating part based on the high frequency clock that is generated by said high frequency clock generating part,
• wherein, in each of the color stations, said light beam source for image writing is driven in synchronization with the pixel clock generated by the pixel clock generation apparatus corresponding to the color station.