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Phase-Locked Loop Pel Clock Filter

IP.com Disclosure Number: IPCOM000046121D
Original Publication Date: 1983-Jun-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Johnson, M: AUTHOR

Abstract

A phase-locked loop can be used to stabilize mechanically derived clock signals in an optical scanner such as is used in a laser printer.

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Phase-Locked Loop Pel Clock Filter

A phase-locked loop can be used to stabilize mechanically derived clock signals in an optical scanner such as is used in a laser printer.

Polygon mirror facet skew errors and angular velocity variations necessitate a dynamic correction of the write clock in scanning laser printers. This is very effectively done using a continuous grating. The laser intensity transmitted through the grating is used to directly clock each pel (print element), and hence it must be both lithographically perfect and, also, free from contamination. Both these demands are expensive to arrange. A conventional phase-locked filter may generate a pel clock independent of grating errors, regions of contamination, defects, etc.

The grating signal is applied to a phase-locked loop (PLL) filter 10 of a time constant chosen to average over a number of grating periods. Single chips containing a voltage-controlled oscillator (VCO) 12, a phase detector 14, a loop filter 10, and amplifier (the whole circuit in fact) are available from many manufacturers at low cost.

The inclusion of such a filter in a laser printer greatly reduces the perfection demanded of a clock grating, obviates the need for expensive sealing and pressurizing of the printhead, and allows use of a full scan grating for accurate clocking, thereby, also, reducing the demands on polygon angular velocity accuracy.

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