Phase-locked loop having separate smoothing and loop filters

Details Phase-locked loop having separate smoothing and loop filters Phase-locked loop having separate smoothing and loop filters

1987-02-26

1988-09-27

Grimm, Siegfried H.

Oscillators

Automatic frequency stabilization using a phase or frequency...

Afc with logic elements

331 8, 331 14, 331 17, 331 27, 331DIG2, H03L 708

Patent

active

047744804

ABSTRACT:
A PLL comprising a phase comparator circuit for detecting the phase of a pulse signal based upon the input signal and the phase of a pulse signal based upon the output signal, a smoothing filter for smoothing the output of the phase comparator circuit, a loop filter for controlling the oscillation frequency on the basis of the smoothing filter, and a voltage controlled oscillator circuit for sending out the output signal having a frequency corresponding to the voltage based upon the output of the loop filter. Since the smoothing filter is separated from the loop filter, time constants of the smoothing filter and the loop filter can be set independently and with precision. If the time constant of the smoothing filter is chosen to be extremely small, for example, the time constant of the phase-locked loop is defined by the time constant of the loop filter. It is thus possible to define the time constant of the phase-locked loop by only selecting the time constant of the loop filter. Further it is possible to both suppress the jitter of the phase-locked loop and reduce the frequency ripple, for example.

REFERENCES:
patent: 4290028 (1981-09-01), Le Grand
patent: 4465982 (1984-08-01), Jernakoff
patent: 4635000 (1987-01-01), Swanberg
Keller et al, "Transmission Design Criteria for a Synchronous Token Ring", IEEE Journal on Selected Areas in Communications, vol. SAC-1, No. 5, Nov. 1983, pp. 721-733.

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