A disciplined clock provides a disciplined time and a disciplined frequency synchronous with a reference clock. The disciplined clock includes: a time receiver to: receive a common view signal from the common view clock; and produce a receiver timing signal; a local clock to: receive a frequency correction; and produce a local timing signal; a time interval counter to: receive the receiver timing signal from the time receiver; receive the local timing signal from the lock clock; and determine a time difference between the receiver timing signal and the local timing signal; and a controller to: receive the time difference from the time interval counter; and communicate the frequency correction, based on the time difference, to the local clock.
Disciplined clocks work by using an external reference source to synchronize the time of their local clock, and to control the frequency of the clock’s local oscillator so that the clock is continuously kept on time. The external reference source for a disciplined clock is typically an radio frequency (RF) signal that originates from a global navigation satellite system (GNSS), such as the U.S. Global Positioning System (GPS), the Russian lobal Navigation Satellite System, or the European Galileo system. Each GNSS system is referenced to a specific time scale that does not meet the legal and/or technical requirements of all applications. This problem is solved by the invention of the multi-source, common-view disciplined clock (MSCVDC) with fail-safe redundancy.
The MSCVDC obtains time synchronization by utilizing the common-view technique to discipline itself to a remote reference time scale. The method involves a common-view signal (CVS) that must be recivable at the location where the reference time scale is located and at all of the locations where MSCVDCs are located. This description utilizes multiple GNSS satellites as the source of the CVS, but signals from other sources could be used as long as they are accessible from all sites. The CVS is simply a vehicle used to transfer time from one site to another, and its own time accuracy is unimportant.
Figure 1 below is a disciplined clock system 200 that includes common view clock 102 to provide common view signal 108, disciplined clock 100 in communication with common view clock 102 to receive common view signal 108 from common view clock 102, reference clock 104 to receive common view signal 110 from common view clock 102 and to communicate reference signal 116, and remote timing analyzer 106 in communication with reference clock 104 to receive reference signal 116 from reference clock 104. Remote timing analyzer 106 produces analyzer signal 114 based on reference signal 116 and communicates analyzer signal 114 to disciplined clock 100. Reference signal 116 can include reference time difference RTD, and analyzer signal 114 can include reference time difference RTD, remote time difference RemTD, and the like, or a combination of the RTD and RemTD. In this manner, disciplined clock 100 can produce disciplined frequency 30 or disciplined time 32 based on reference time difference RTD or remote time difference RemTD.
This clock is more versatile than a GNSS disciplined clock because it allows the user to select the time scale that is used to discipline the clock. For example, for some applications, NIST time (and not GPS time) is required for legal and/or technical reasons. This clock can synchronize to the time kept by NIST, or by any other timing laboratory, through the common-view approach. This clock also provides fail-safe layers of redundancy that a GNSS disciplined clock does not provide. For example, if the network link to common-view data is unavailable, the clock can automatically switch to time obtained through GNSS satellites to provide holdover until the network connection is restored. If the reference time scale is unavailable, the clock can automatically switch to another time scale simply by accessing common-view data from that time scale.