Browse Prior Art Database

VARIABLE FREQUENCY PIXEL CLOCK GENERATOR WITH PHASE LOCK LOOP

IP.com Disclosure Number: IPCOM000026513D
Original Publication Date: 1992-Aug-31
Included in the Prior Art Database: 2004-Apr-06
Document File: 2 page(s) / 121K

Publishing Venue

Xerox Disclosure Journal

Abstract

In general, laser printers employ a pixel clock signal to indicate pixel positions as the laser beam is scanned across a photoresponsive surface by a reflecting polygon. In laser printers which employ an end of scan (EOS) detector, for detecting the end of a raster of pixels, the pixel clock is typically phase locked to the polygon drive motor via an EOS detector in order to compensate for low frequency changes in the motor velocity. In addition, fast-scan magnification, along the raster output direction, is accomplished by varying the spacing or resolution of the pixels placed along a single raster. More specifically, the fast scan magnification is directly related to the pixel clock frequency, as the pixel clock determines the output of individual pixels along the raster.

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XEROX DISCLOSURE JOURNAL

VARIABLE FREQUENCY PIXEL Proposed Classification CLOCK GENERATOR WITH PHASE U.S. C1.307/106 LOCK LOOP Int. C1. H03K 3/00,3/64 Arm Nacman

r-- I

2P I 92

- rl

--

-- PIXEL

CLOCK

+4 *

PRESCALER

+

iMUX

+N

',C.a.l

53 TO 148 MHZ

7

END OF COUNT

DETECTOR

T

INTEGRATOR

SUMMING AMPLIFIER

COMPOSITE SIGNAL

CENTER FREQUENCY VOLTAGE

XEROX DISCLOSURE JOURNAL - Vol. 17,Xo. 4 JulyiAugust 1992 199

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Page 2 of 2

VARIABLE FREQUENCY PIXEL CLOCK GENERATOR WITH PHASE LOCK LOOP(Cont'd)

In general, laser printers employ a pixel clock signal to indicate pixel positions as the laser beam is scanned across a photoresponsive surface by a reflecting polygon. In laser printers which employ an end of scan (EOS) detector, for detecting the end of a raster of pixels, the pixel clock is typically phase locked to the polygon drive motor via an EOS detector in order to compensate for low frequency changes in the motor velocity. In addition, fast-scan magnification, along the raster output direction, is accomplished by varying the spacing or resolution of the pixels placed along a single raster. More specifically, the fast scan magnification is directly related to the pixel clock frequency, as the pixel clock determines the output of individual pixels along the raster.

Traditionally, the adjustment of the fast-scan magnification level has been limited to only a few percent, due to the inability of the phase lock loop to stay locked over a wide range of pixel clock frequencies. The present design eliminates this problem and enables a greater fast-scan magnification range. The relevant portions of the design are illustrated in the figure, and those components that are commonly known, or not essential to the disclosure will not be discussed in detail. Basically, there are three elements of the design that enable the phase lock l...