Horology: time measuring systems or devices – Chronological – With auxiliary illumination for display
Patent
1995-06-15
1996-07-23
Miska, Vit W.
Horology: time measuring systems or devices
Chronological
With auxiliary illumination for display
368227, 3151693, 345102, G04B 1930, G09G 310, G09G 336
Patent
active
055397077
ABSTRACT:
An electroluminescent lamp driver system for driving or powering an electroluminescent lamp to illuminate the display in an electronic watch, such as a quartz analog watch, uses the counter in a CMOS timekeeping chip which counts down the quartz oscillator frequency to one Hz for an analog quartz watch. The counter provides a plurality of pulse trains which are combined in digital logic to provide switching signals. The digital logic is included in the timekeeping chip and is implemented in low voltage bulk CMOS. A high voltage is required to drive the lamp and it is provided in a separate chip containing a high voltage inverter in which current is switch through an inductor in response to the switching signals from the timekeeping chip. The efficiency of the inverter is improved by generating, in the timekeeping chip, switching signals in the form of pulse trains which are asymmetric and have a duty cycle of greater than 50% to operate the switch when the output voltage from the bridge is in one-half of the AC output voltage across the lamp (the capacitance of the lamp is being charged) and has a duty cycle of less than 50% during the second half of the AC cycle when the capacitance of the lamp is being discharged. The system architecture segregates the high voltage and low voltage circuitry, eliminates redundant elements (a separate low frequency oscillator) and the digital logic for providing the pulse trains which produce switching in the inverter is located in the timekeeping chip where it may be implemented at lower cost than in the high voltage inverter chip.
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Harris Corporation
Miska Vit W.
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