Sub-pixel generation for high speed color laser printers using a clamping technique for PLL (phase locked loop) circuitry
AssigneeXerox Corporation
InventorMostafa R. Yazdy
Life of this patent
Estimating the term…
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. An optimizing circuit is associated with a sub-pixel clock generator for clamping an input voltage to a voltage controlled oscillator controlling clock frequency between a desired range. The clamping circuitry comprises a comparator for detecting when the voltage has moved out of the desired range and then charges or discharges a loop filter circuit controlling the input voltage to the VCO to keep the input voltage within the desired range.
Claims14
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, a charge pump circuit and a loop filter disposed to set an input voltage at a VCO to generate a desired frequency corresponding to the first system printing speed;
- a clamping circuit associated with the sub-pixel clock generator for settling jitter and avoiding saturation of the input voltage to the VCO upon applying a second reference signal corresponding to a second system printing speed to the sub-pixel clock generator;
- and
- an ROS light source in operative communication with the sub-pixel clock generator for sub-pixel control of the 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;
- switching the first reference signal to a second reference signal corresponding to a second system printing speed;
- clamping the input voltage to the VCO during the switching for settling jitter and avoiding saturation of the input voltage to the VCO;
- and
- communicating the VCO output frequency corresponding to the second system printing speed to the ROS light source.
A xerographic printing 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, a charge pump circuit and a loop filter disposed to set an input voltage at a VCO to generate a desired frequency corresponding to the first system printing speed;
- and
- a clamping circuit associated with the sub-pixel clock generator for settling jitter and avoiding saturation of the input voltage to the VCO upon applying a second reference signal corresponding to a second system printing speed to the sub-pixel clock generator.
Dependencies are inferred from the claim text.