Oscillators – Automatic frequency stabilization using a phase or frequency... – Afc with logic elements
Reexamination Certificate
1999-02-24
2001-06-12
Kinkead, Arnold (Department: 2817)
Oscillators
Automatic frequency stabilization using a phase or frequency...
Afc with logic elements
C331S046000, C370S350000, C375S356000, C375S354000, C327S141000, C327S151000, C327S160000
Reexamination Certificate
active
06246291
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of synchronizing a local oscillator signal to a main oscillator signal in a network.
The present invention also relates to a device for performing a method of the invention, and a communication device comprising such a device.
2. Description of the Related Art
Such a method and device are known from European Patent Application EP-A-0613276. The known method and device perform synchronisation between a central unit and several base stations by means of transferring synchronisation information possibly including sync opportunity information and time delay information. This enables a base station receiving the synchronisation information to detect with which time delay after receipt of the sync opportunity information synchronisation of its clock is actually to be carried out. A clock counter in each respective base station is preloaded to a respective value defined by the transmitted delay information. At zero count all base station clocks synchronize momentarily. Similar synchronization may take place with a given reference signal. It is a disadvantage of the known method and device that, if handsets coupled to respective base stations are communicating with one another, synchronisation after a temporary disruption of information from the central unit and performed in a way as indicated above, will lead to a possible loss of synchronisation of mutually communicating handsets upon reappearance of the sync information. Such a situation can similarly arise in a DECT (Digital European Cordless Telephone) protocol system, where a connection to an ISDN network may be subjected to a temporarily disappearing and/or reappearing reference signal given by the ISDN network. Neither case may, however, lead to an interruption, or disturbance of or a phase jump in ongoing communication between, for example, the handsets.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a method and device presenting a solution to the general problem of resynchronising clocks in devices of a network.
To this end, in a method of the invention, the phase shift is being used as an at least initially fixed reference phase shift between the thus synchronized local oscillator signal and the main oscillator signal. In a device of the invention, the synchronizing means comprise means for fixing the phase shift and synchronizing the future oscillator signal based on said fixed phase shift. It is an advantage of the method and device according to the invention that the phase shift experienced after reappearance of the main oscillator signal is simply being used to base the synchronised local oscillator signal thereon, as a result of which no interruption or phase jumps will occur. Synchronisation now takes place in a way that an initially fixed phase shift is maintained between the main oscillator signal and the local oscillator signal. Thus after applying the method according to the invention, processing based on the synchronised local oscillator signal in the device has a fixed delay relative to processing based on the main oscillator signal. In a DECT environment this has the additional advantage that handsets communicating through the base station, where a further handset starts communication through the ISDN network which makes the main oscillator signal reappear, will now not be disturbed by the smooth synchronisation method according to the invention.
In an embodiment of the method according to the invention the initial phase shift is being determined upon reappearance of the main oscillator signal, whereafter the initial phase shift is substantially maintained for a period of time. Easy control is possible in a further embodiment according to the present invention, wherein the initial phase shift is being controlled step-by-step by influencing the dividing ratio of a reference counter.
In a further embodiment of the method according to the present invention, wherein the initially fixed reference phase shift is being diminished by gradually controlling the frequency of the local oscillator accordingly, timing margins can be recovered and gained in order to be capable of accommodating time delays or time shifts caused by data, cable or air delays.
REFERENCES:
patent: 4803705 (1989-02-01), Gillingham et al.
patent: 5684788 (1997-11-01), Krech
patent: 0613276A1 (1994-08-01), None
Schuur Cornelis C. M.
Vos Hermanus J. M.
Kinkead Arnold
U.S. Philips Corporation
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