1. Technical Field
The present invention relates to a reference signal generation device, an electronic device, a moving object, a data communication device, and a terrestrial digital communication network.
2. Related Art
A global positioning system (GPS) which is one of global navigation satellite systems (GNSS) using a satellite has been widely known. An atomic clock having significantly high precision is mounted in a GPS satellite used in the GPS. A satellite signal on which orbit information, accurate time information, or the like of a GPS satellite is superimposed is transmitted to the ground. The satellite signal transmitted from the GPS satellite is received by a GPS receiver. The GPS receiver performs processing of calculating the current position or the current time information of the GPS receiver, processing of generating an accurate timing signal (1 PPS) synchronized with the coordinated universal time (UTC), or the like based on the orbit information or the time information superimposed on the satellite signal.
As such a GPS receiver, a GPS receiver in which a normal positioning (position estimation) mode in which a position and time are provided, and a position fixed mode in which time is provided through fixed location positioning at a known position, are provided based on positioning calculation is generally used.
In the normal positioning mode, satellite signals from the predetermined number or more (three is the minimum if being used for two-dimensional positioning, and four is minimum if being used for three-dimensional positioning) of GPS satellites are required. As the number of GPS satellites which enable reception of the satellite signal is increased, the accuracy of the positioning calculation becomes more improved.
In the position fixed mode, if position information of the GPS receiver is set, 1 PPS can be generated as long as the satellite signal can be received from at least one GPS satellite.
Here, in terrestrial digital broadcasting, a reference signal generation device including the GPS receiver and an atomic oscillator is used. Because the terrestrial digital broadcasting is public broadcasting, suspension of the broadcasting occurring due to failure in the atomic oscillator is not permitted. Thus, generally, two reference signal generation devices are prepared, and one thereof is used. In a case where the reference signal generation device which is being used fails, switching to another reference signal generation device is performed.
JP-A-2011-155367 discloses a reference frequency generation device which includes a GPS receiver, an atomic oscillator, a crystal oscillator, and a phase locked loop (PLL), and outputs the 1 PPS. The reference frequency generation device is configured such that, firstly, the atomic oscillator is used, and in a case where the atomic oscillator fails, switching to the crystal oscillator is performed.
However, in the device disclosed in JP-A-2011-155367, switching to the crystal oscillator is performed after the atomic oscillator fails. Thus, using such a device for satisfying a strict request as in the terrestrial digital broadcasting is difficult.