Frequency modulation in a phase-locked loop

Details Frequency modulation in a phase-locked loop Frequency modulation in a phase-locked loop

1984-02-21

1985-10-08

LaRoche, Eugene R.

Modulators

Amplitude modulator

Nonlinear device controlled by modulating signal

332 23R, 455113, H03C 300

Patent

active

045463310

ABSTRACT:
Apparatus is provided to frequency modulate (FM) RF carrier frequencies generated in a phase-locked loop (PLL). FM outside the loop bandwidth is AC coupled to the loop. FM within the loop bandwidth is DC coupled via an integrating OP-AMP to provide phase modulation. Whenever the output of the integrator exceeds a preset threshold, a prescaler removes or adds two pi (or integral multiples of two pi) radians of phase change from the input to the loop divide-by-N circuit. At the same time, a current source pumps charge into the integrator to exactly compensate for the amount of phase removed or added resetting the integrator. DC feedback around the integrating OP-AMP and a feedback signal proportional to the exact amount of phase added or removed provides a true synthesized loop center frequency with no drift. When the feedback path is interrupted, DC FM is provided.

REFERENCES:
patent: 4052672 (1977-10-01), Enderby et al.

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