Apparatus for generating a common output signal as a function of

Details Apparatus for generating a common output signal as a function of Apparatus for generating a common output signal as a function of

1982-08-30

1985-04-16

LaRoche, Eugene R.

Oscillators

Automatic frequency stabilization using a phase or frequency...

Plural a.f.s. for a single oscillator

331 14, 331 25, H03L 722

Patent

active

045118590

ABSTRACT:
A circuit for generating a common signal as a function of either of two reference signals comprises a pair of phase-locked loops which share an oscillator. Each phase-locked loop generates a control signal as a function of one of the reference signals. One or the other of the control signals is coupled to the oscillator which generates the common signal. A comparator compares the two control signals and generates a signal indicative of their difference. While the control signal generated by the first phase-locked loop is coupled to the oscillator, the difference signal is applied to the second phase-locked loop where it controls the generation of the second control signal to minimize the difference between the two control signals. While the control signal generated by the second phase-locked loop is coupled to the oscillator, the second phase-locked loop is nonresponsive to the difference signal. Thus when a switch of reference signals occurs even if they are of different phase and even if that phase is slowly time-varying, the circuit can lock to the new reference signal at a phase dictated by the phase difference between the two references at the instant of the switch without causing the oscillator output to undergo significant frequency or phase changes.

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The Bell System Technical Journal, vol. 10, No. 6, Jul.-Aug. 1981, R. Metz et al.: "Network Clock Synchronization", pp. 1109-1129.
International Switching Symposium, Montreal, Sep. 21-25, 1981, IEEE, New York (US) C. C. Probert: Synchronization Between DMS Exchanges", Session 42A, Paper 5, pp. 1-6.
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