HIGH-STABILITY CLOCK SIGNAL REGENERATOR WITH A STABLE FIXED FREQUENCY BACKUP CLOCK GENERATOR

A clock signal regenerator comprising a frequency control loop (1, 2, 3, 4) which comprises a variable-frequency clock signal generator (2) used in digital telephone exchanges, when a local clock signal must be generated from incoming clock signals (1-1, 1-N). The clock signal regenerator comprises a very stable auxiliary signal generator (9) and a first difference signal producer (11) for determining the frequency difference between the generated clock signal and the auxiliary signal. This frequency difference is determined periodically and written into a storage device (13). In addition, the regenerator comprises a second difference signal producer (14) in which the difference is determined between a new frequency difference determined in the first difference signal producer (11) and the preceding frequency difference stored in the storage arrangement (13). After the incoming clock signals (1-1, . . . 1-N) have dropped out the difference signal produced in the second difference signal producer (14) is applied as a control signal to the clock signal generator (2), and the content of the storage device ( 13) is not changed. This has the advantage that the stability of the clock signal regenerator is then the same as the stability of the auxiliary signal generator.