Browse Prior Art Database

THERMAL BRIDGE CIRCUIT ONBOARD INK-JET HEATER DIE

IP.com Disclosure Number: IPCOM000026788D
Original Publication Date: 1993-Aug-31
Included in the Prior Art Database: 2004-Apr-06
Document File: 4 page(s) / 145K

Publishing Venue

Xerox Disclosure Journal

Abstract

Two thermally sensitive NMOS devices are combined in a bridge circuit on board a thermal ink jet (TIJ) heater chip to sense printhead temperature and to provide a signal to circuits which provide compensation for a temperature rise, thereby maintaining conditions necessary for high quality printing. The spot-size generated by a TIJ printer must be constant regardless of changes in printhead temperature when certain applications require a high-quality output.

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XEROX DISCLOSURE JOURNAL

THERMAL BRIDGE CIRCUIT Proposed Classification ONBOARD INK-JET HEATER DIE
Joseph J. Wysocki Thomas A. Tellier Int. C1. HOll23/02 William G. Hawkins Gary A. Kneezel
Joseph F. Stephany Richard LaDonna
Michael Poleshuk
Thomas E. Watrobski

U.S. C1.357/081

+V

XEROX DISCLOSUm JOURNAL - VO~. 18, NO. 4 July/August 1993 443

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THERMAL BRIDGE CIRCUIT ONBOARD INK-JET HEATER DIE

(Cont'd)

Two thermally sensitive NMOS devices are combined in a bridge circuit on board a thermal ink jet (TIJ) heater chip to sense printhead temperature and to provide a signal to circuits which provide compensation for a temperature rise, thereby maintaining conditions necessary for high quality printing. The spot-size generated by a TIJ printer must be constant regardless of changes in printhead temperature when certain applications require a high-quality output. There are two distinct approaches for achieving constant spot size, one in which the temperature of a printhead is maintained constant and the other in which the temperature of a printhead is not controlled but the heater pulsing conditions (pulse width and burn voltage) are changed to accommodate the printhead's change in temperature. Regardless of the approach, a suitable sensor is required to sense chip temperature, one which is sensitive to changes which affect drop size and yet are immune to fluctuations in ambient temperature. A bridge circuit is the favored basic sensor design since it has particular advantages when placing as much of the thermal sensing and control devices as possible on a single heater chip. For example a full-width TIJ printer array that is composed of a multiplicity of heater chips, requires the bridge elements and control circuitry to be compatible with NMOS technology.

The bridge circuit shown in Figure 1 comprises thermistors Rp and Rt which for sake of discussion are assumed to be equal in value at room temperature. The defining equation for the effective thermal coefficient,

is defined in terms of temperature T and the thermal coefficients a of the thermistors R and Rt. It is clear that the thermal coefficients must be different and tiat the highest sensitivity occurs when the thermal coefficients are as different as possible, including different sign.

Two thermistors which are compatible with printhead fabrication have been adapted for use in TIJ devices, both of which are suitable for th...