Title: Digital watch with oscillator/divider power selection circuitry

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Abstract: A digital watch with oscillator/divider power selection circuitry. The selection circuitry selects the source of the voltage to be supplied to the crystal oscillator and initial divider circuits. If battery voltage is low because battery current is high, as when the light emitting diodes (LED's) are illuminated in an LED digital watch or when the illumination light is on in a liquid crystal display (LCD) digital watch, the crystal oscillator and initial divider would be powered by two batteries; and when battery voltage is high because battery current is low, the crystal oscillator would be powered by only one battery. Therefore, the power selection circuitry determines whether one or two batteries are used to power the oscillator depending upon the particular operating conditions. There are two advantages of this technique: (1) current is reduced so battery life is increased, and (2) the voltage never goes so low that circuit production yields are adversely affected. The power selection circuitry includes a plurality of metal oxide semiconductor field effect transistors (MOSFET's) and an input signal, which determines whether one battery is needed to power the oscillator because the LED's are not illuminated or two batteries are needed to power the oscillator because the LED's are illuminated.


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