Pixel clock generator, optical scanner and image forming device incorporating same
A pixel clock generator device includes a high frequency clock generator, a phase shift data generator to generate phase shift data for controlling a phase shift amount of a pixel clock, a phase shift data pattern generator to read the phase shift data from the phase shift data generator, generate a pattern of the phase shift data for output, and when outputting a same phase shift data pattern for consecutive scan lines, generate, for a next scan line, a phase shift data pattern in which a pixel clock at a position moved by a random number of pixel clocks from a phase-shift position of a pixel clock in a phase shift data pattern for a current scan line is phase-shifted, and a pixel clock generator to generate, on the basis of a high frequency clock, a pixel clock phase-shifted in accordance with the generated phase shift data pattern.
1. A pixel clock generator device, comprising:
a high frequency clock generator to generate a high frequency clock;
a phase shift data generator to generate phase shift data for controlling a phase shift amount of a pixel clock;
a phase shift data pattern generator to read the phase shift data from the phase shift data generator, generate a pattern of the phase shift data for output, and when outputting a same phase shift data pattern for consecutive scan lines, generate, for a next scan line, a phase shift data pattern in which a pixel clock at a position moved by a random number of pixel clocks from a position of a pixel clock phase-shifted in a phase shift data pattern for a current scan line is shifted in phase;
a pixel clock generator to generate, on the basis of the high frequency clock, a pixel clock phase-shifted in accordance with the generated phase shift data pattern, and
a pseudo random pattern generator to output a pseudo random pattern as a number of the random number of pixel clocks.
2. The pixel clock generator device according to claim 1 , wherein the pseudo random pattern is generated by Modulo-2 division.
3. The pixel clock generator device according to claim 1 , wherein the pseudo random pattern generator is configured to apply, for the next scan line, a pseudo random pattern for a scan line after the next scan line when a difference in the pseudo random patterns for the current and next scan lines matches an integral multiple of a phase-shift cycle of a pixel clock.
4. The pixel clock generator device according to claim 1 , wherein the pseudo random pattern generator uses a primitive polynomial.
5. The pixel clock generator device according to claim 1 , wherein the pseudo random pattern generator includes a dedicated lookup table containing the pseudo random pattern.
6. The pixel clock generator device according to claim 1 , wherein a cycle of the pseudo random pattern is selectable.
7. The pixel clock generator device according to claim 6 , further comprising
a plurality of pseudo random pattern generators with different cycles, wherein
a minimal-order pseudo random pattern generator satisfying a cycle into which a pixel clock is inserted for phase shift is operated while the other-order pseudo random pattern generators are placed in sleep state.
8. An optical scanner, comprising:
a light source;
a deflector to deflect a light beam output from the light source;
an optical guide to guide the light beam deflected by the deflector to a target medium; and
the pixel clock generator device according to claim 1 , wherein
the light source is driven in synchronization with the pixel clock generated by the pixel clock generator.
9. An image forming device comprising the optical scanner according to claim 8 .