Gradual charge pump technique for optimizing phase locked loop (PLL) function in sub-pixel generation for high speed laser printers switching between different speeds
AssigneeXerox Corporation
InventorMostafa R. Yazdy
Life of this patent
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Abstract
Methods and apparatus for optimizing the phase lock loop circuitry of sub-pixel clock generators for situations where frequent switching between different system printing speeds, and hence clock frequencies are required. A timing control logic circuitry is associated with the sub-pixel clock generator for a graduated change in charge pump current. The timing control logic circuitry comprises a plurality of current generators serially connected with the charge pump current via associated switches for the selective adjustment of charge pump current in a graduated manner.
Claims7
A switchable ROS driver circuit for an electrophotographic system for:
- selective switching between a plurality of system printing speeds comprising:
- a sub-pixel clock generator tuned to a first reference signal corresponding to a first printing system speed and including a phase locked loop circuit and a charge pump circuit for setting an input voltage at a VCO to generate a desired frequency corresponding to the first system printing speed;
- a control circuit associated with the sub-pixel clock generator for selective and incremental adjustment of the input voltage to the VCO for generating an other desired frequency corresponding to a second system printing speed;
- and
- an ROS light source in operative communication with the sub-pixel clock generator for sub-pixel control of an ROS light source.
A method for switching an ROS driver circuit for an electrophotographic system for selective switching of system printing speeds, comprising:
- applying a first reference signal corresponding to a first system printing speed to a pixel clock generator disposed to set an input voltage at a VCO in communication with an ROS light source for generating a first desired frequency corresponding to the first system printing speed, wherein the input voltage to the VCO comprises an output from a charge pump circuit;
- adjusting the output of the charge pump circuit in graduated adjustments for generating a second input voltage to the VCO for generating a second desired frequency corresponding to a second system printing speed, and
- communicating the VCO output frequency corresponding to the second system printing speed to the ROS light source.
Dependencies are inferred from the claim text.