Patent
1976-07-23
1977-08-16
Robinson, Thomas A.
H04J 306
Patent
active
040427811
ABSTRACT:
A circuit arrangement is disclosed for synchronizing the oscillators of a digital telecommunications network. The network nodes of a PCM t.d.m. telecommunications network contain mutually synchronizing exchange pulse train oscillators. In each of the network nodes, a first pulse sequence is formed from the line pulse trains of the digital telecommunications lines in accordance with a pulse train frequency reduction factor. A second pulse sequence is formed in each of the network nodes by the exchange pulse train oscillator in accordance with the pulse train frequency reduction factor. Phase discriminators formed by logic-linking circuits are individually assigned and connected to the digital telecommunications lines. Phase differences between the first pulse sequence associated with the line pulse train and the second pulse sequence associated with the relevant exchange pulse train are detected by the phase discriminator. These detected phase difference signals can be combined in a sum or mean value circuit. As a result of these phase difference signals, a frequency regulating signal is generated which regulates the frequency of the exchange pulse train oscillator in each of the network nodes. In the circuit arrangement of this invention, the phase discriminator signal is maintained within a constant zone on both sides of a linear range. Each overshooting and undershooting of a .+-. n2 .pi.stage (n = 0, 1, 2, . . . N) of the phase difference between the first sequence (the line pulse train pulse sequence) and the second sequence (the exchange pulse train pulse sequence) is digitally counted in a counting device with a counting volume N. A first special control input of the phase discriminator receives a first special control input which maintains the phase discriminator in a starting state corresponding to a phase difference of +2.pi.. This first special control signal is generated when the counting device indicates that the count of the overshooting of the +n2.pi. stages exceeds the count of the undershooting of +n2.pi. stages. In like manner, second special control input of the phase discriminator receives a second special control signal which maintains the phase discriminator in a starting state corresponding to a phase difference of -2.pi.. This second special control signal is generated when the counting device indicates that the count of the undershooting of -n2.pi. stages exceeds the count of the overshooting -n2.pi. stages.
REFERENCES:
patent: 3869579 (1975-03-01), Karl
patent: 3970796 (1976-07-01), Gyurki
patent: 4002839 (1977-01-01), Karl et al.
Robinson Thomas A.
Siemens Aktiengesellschaft
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