Patent ID: 7551911

Claim:
A battery operated wireless communication device comprising: a wireless receiver operable to receive radio signals carrying digital messages and to extract the digital messages there from; a reference oscillator operable to produce a reference oscillator clock; a sleep oscillator operable to produce a sleep oscillator clock; and a dual mode timer for continually maintaining system time based upon a reference counter output while operating in an active mode and based upon a sleep counter output when operating in a sleep mode, the dual mode timer including: a reference counter operable to produce the reference counter output based upon the reference oscillator clock and a reference counter modulus when in the active mode; a sleep counter operable to produce the sleep counter output based upon the sleep oscillator clock and a sleep increment value, wherein the sleep increment value is based upon an estimated number of frames per sleep clock cycle; and calibration circuitry operable to set the sleep increment value prior to the dual mode timer transitioning from the active mode to the sleep mode.