Thermal inkjet printhead warming circuit

摘要

For each printhead nozzle, nozzle circuitry includes a warming transistor, drive transistor and heating resistor. To maintain a threshold temperature at the printhead, a warming pulse is sent from the warming transistor to the heating resistor of one or more nozzles when the temperature falls below a prescribed temperature. To fire a nozzle a firing pulse is output from the drive transistor to the heating resistor. The warming transistor is laid out as a segmented portion of the drive transistor layout area. No layout penalty is incurred by including the warming transistor for each nozzle. The source of a warming transistor is coupled in common to the source of a drive transistor. The drain of the warming transistor is coupled in common to the drain of the drive transistor. The gates are separate. The gates receive respective warming or firing control signals. The drains are coupled to the heating resistor.