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Abstract

A technique for activating an active-mode high frequency clock following a sleep period for use within a mobile station wherein selected components of the mobile station operate using a low power, low frequency sleep-mode clock during the sleep period and the faster high frequency active-mode clock during non-sleep periods. In one embodiment, the technique is implemented by a device having a wake-up estimation unit for estimating a wake up time using the sleep-mode clock and a frequency drift compensation unit for compensating for any error in the estimated wake up time caused by frequency drift in the sleep-mode clock. An off-set time compensation unit is also provided for compensating for a lack of precision in the low frequency sleep-mode clock resulting in a possible error in the estimated wake up time. The lack of precision can result in an initial timing off-set error at the beginning of the sleep period and an final timing off-set error at the end of the sleep period. Both the frequency drift compensation unit and the off-set time compensation unit employ a high frequency transition-mode clock signal for use in calculating the time required to adjust the wake-up time. The transition-mode clock, which may have the same frequency as the active-mode clock, is employed only at the beginning and end of the sleep period and is deactivated throughout most of the sleep period to reduce power consumption.

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