Frequency modulated phase-locked loop signal source

Details Frequency modulated phase-locked loop signal source Frequency modulated phase-locked loop signal source

1980-07-14

1982-03-23

Britton, Howard

Pulse or digital communications

Repeaters

Testing

455113, H04B 104, H03B 304, H04L 2712, H04L 2720

Patent

active

043217060

ABSTRACT:
A programmable phase-locked loop frequency synthesizer having a feedback path that includes a tuned discriminator circuit is frequency modulated by coupling a portion of the modulating signal into the feedback path to effect modulation at rates which exceed the bandwidth of the phase-locked loop and by utilizing a portion of the modulating signal to frequency modulate the phase-locked loop reference signal to effect modulation at rates within the bandwidth of the phase-locked loop. A digitally controlled phase shifter that forms a portion of the discriminator tuning circuits in effect divides the phase-locked loop tuning range into a series of relatively narrow centiguous frequency bands. Data, representing deviations in the discriminator characteristics for each of these frequency bands, are stored in an erasable programmable read only memory. As the phase-locked loop is tuned to a particular frequency, a microprocessor determines the associated frequency band, accesses the stored data appropriate to that frequency band and establishes the proper setting of the digitally controlled phase shifter. The accessed data is coupled to a multiplying digital to analog convertor to automatically adjust the level of the modulating signal so that the system exhibits relatively constant modulation characteristics for each frequency band within the tuning range of the phase-locked loop. Low distortion is achieved within each of the relatively narrow frequency bands by circuitry which reduces or eliminates amplitude variations within the feedback path that includes the discriminator circuit, band pass filtering within this feedback path, and a feed-forward circuit arrangement that prevents modulation components from adversely affecting the discriminator tuning circuits. Additionally, a gain switching arrangement that automatically reduces the gain of the feedback loop and the phase-locked loop gain ensures system stability for all operating and tuning conditions.

REFERENCES:
patent: 4052673 (1977-10-01), Herzog
patent: 4068198 (1978-01-01), Otto
patent: 4110707 (1978-08-01), Giolma
patent: 4206425 (1980-06-01), Nossen

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