Patent ID: 7084810
Filing Date: 2006-08-01
Classification: G01S

Abstract:
1. A portable terminal comprising: a GPS processing unit which receives a radio wave from a GPS satellite and specifies a current position; and an RTC oscillator which continuously generates and outputs real time clocks even in a power saving mode, wherein said GPS processing unit comprises a free run RTC counter which continuously counts real time clocks generated by said RTC oscillator even in the power saving mode, a time maintenance processing unit which compnses a memory storing a count value of the free run RTC counter and a notified GPS time upon a shift from a normal power mode to the power saving mode, calculates a duration of the power saving mode from a difference between the count value stored in the memory and the count value read from the free run RTC counter upon return from the power saving mode to the normal power mode, and calculates a current GPS time by adding the calculated duration of the power saving mode to the GPS time stored in the memory upon a shift from the normal power mode to the power saving mode, and a position measurement processing unit which performs position measurement by receiving a radio wave from the GPS satellite in the normal power mode, also notifies the time maintenance processing unit of a GPS time acquired when position measurement is performed, and performs position measurement by using the GPS time notified from the time maintenance processing unit upon a shift from the power saving mode to the normal power mode; and wherein the time maintenance processing unit calculates in advance an error in a frequency of the real time clock.