Phase locked loop variable frequency generator

Details Phase locked loop variable frequency generator Phase locked loop variable frequency generator

1978-11-09

1980-05-20

Grimm, Siegfried H.

Oscillators

Automatic frequency stabilization using a phase or frequency...

Plural a.f.s. for a single oscillator

331 14, 331 16, 331 25, H03B 304

Patent

active

042041740

ABSTRACT:
The invention relates to phase locked loops in which a variable-frequency voltage-controlled oscillator (VCO) feeds a phase comparator via an adjustable divider having a division factor N. The comparator compares the phases of the divided frequency (Fd) and a reference frequency (Fr), and adjusts the VCO to produce phase equality. To enable the VCO frequency (FO) to be adjusted in smaller steps than Fr and yet maintain a loop bandwidth greater than the step size with good spurious performance (thus providing a "fractional N synthesizer"), Fo is made slightly more than N.Fr. The phase detector thus produces a phase error signal. At periodic instants, determined by the period of the frequency difference between Fo and N.Fr, a control unit temporarily increases N by unity so as to bring Fd and Fr into phase. To eliminate the sawtooth waveform that would otherwise be produced on the phase error signal, the control unit also produces unit increases in N during each such period so as to produce a phase difference between Fd and Fr which is opposite in sign to, and substantially offsets, the integrated value of the phase differences up to that instant. The phase error signal therefore undergoes only residual variations, and these are backed off by an analogue output derived from the control unit.

REFERENCES:
patent: 3516007 (1970-06-01), Bos et al.
patent: 3872397 (1975-03-01), Hanneman
patent: 3928813 (1975-12-01), Kingsford-Smith

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