A generic navigation satellite system (GNSS) signal receiver having a fast
time to first fix by calibrating a low power always-on real time clock
(RTC). The receiver includes an RTC calibrator having a fraction
calculator. The RTC calibrator may also include a time expander. Before
the receiver is powered off, the fraction calculator uses the fine
resolution of GNSS time for determining a time fraction for RTC time.
When the receiver is powered back on, the time expander uses an estimate
of RTC time drift during the time that GNSS receiver had power off and
the time fraction for calibrating and increasing the resolution of the
RTC time for an RTC time tick. A signal navigation processor uses the
calibrated RTC time for assisting a first fix with code phase search,
integration time periods, resolution of epoch integer and/or
location-in-space of GPS satellites.