Phase locked loop frequency and phase modulators
AssigneeMarconi Instruments Limited
InventorDavid P. Owen
Life of this patent
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Abstract
A signal generator is arranged to produce frequency or phase modulation at frequencies which extend from a high value down to zero, i.e. to a d.c. level shift. The output oscillator forms part of a phase locked loop which also includes a variable frequency divider. A modulation signal is applied to the loop, so that high frequency modulation signals directly modify the control signal which determines the frequency of the oscillator, and so that low frequency modulation signals alter the divisor value of the variable frequency divider so as to modify the frequency characteristics of the phase locked loop. Quantization noise is reduced by applying a masking signal to an analogue-to-digital converter which utilizes the low frequency modulation signals to alter the divisor value.
Claims13
A modulation signal source including a phase locked loop having a variable frequency oscillator;
- a variable frequency divider and a dual input phase detector, the frequency of said oscillator being dependent upon the value of a control signal derived from said phase detector;
- a source of reference frequency signals, the phase detector being operative to compare the frequency of a signal received from said oscillator via said divider with the frequency of a signal derived from the source of reference frequency signals;
- means for receiving a modulation signal and for utilising it to adjust said control signal;
- digital means responsive to said modulation signal to vary the divisor value of said frequency divider;
- and means for also feeding a masking signal to said digital means so as to reduce the effect of digital quantisation noise on the frequency characteristic of the phase locked loop.
A modulation signal source including a phase locked loop having a variable frequency oscillator;
- a variable frequency divider a dual input phase detector, and a low pass filter, the frequency of said oscillator being dependent upon the value of a control signal derived from said phase detector and fed to it via said low pass filter;
- a source of reference frequency signals, the phase detector being operative to compare the frequency of a signal received from said oscillator via said divider with the frequency of a signal derived from the source of reference frequency signals;
- means for receiving a modulation signal and for utilising it to adjust said control signal;
- analogue-to-digital conversion means responsive to said modulation signal to vary the divisor value of said frequency divider;
- and means for producing at said conversion means a masking signal having a frequency below that of said reference frequency signals and above that of the cut-off value of said low pass filter, whereby the output signal of said oscillator is modulated in accordance with said modulation signal.
Dependencies are inferred from the claim text.