Phase locked loop for direct modulation

Details Phase locked loop for direct modulation Phase locked loop for direct modulation

1989-09-20

1990-08-28

Grimm, Siegfried H.

Modulators

Frequency modulator

Including stabilization or alternatively distortion, noise...

331 8, 331 17, 332127, H03C 306, H03L 7085

Patent

active

049528882

ABSTRACT:
A PLL for direct modulation having a flat modulation characteristic in the audio frequency range is described. The PLL for the direct modulation comprises a voltage controlled oscillator whose oscillating frequency is controlled by an output voltage of a low pass filter and also modulated by a signal, a programmable frequency divider supplied with an output signal of the voltage controller oscillator or the output signal divided in frequency, and a phase comparator comparing an output frequency f.sub.p of the programmable frequency divider with a reference frequency f.sub.r. The phase comparator outputs signals indicating three conditions in accordance with the results of the comparison: a first transistor turned ON by the output signal of the phase comparator indicating the condition f.sub.r >f.sub.p for charging a capacitor within the low pass filter; a second transistor turned ON by the output signal of the phase comparator indicating the condition f.sub.r >f.sub.p for constituting the discharging path of the capacitor within the low pass filter; and both transistors being turned OFF for the condition f.sub.r =f.sub.p. A delay means is inserted in the first transistor circuit for delaying the timing at which the first transistor turns ON. The delay mens causes the self resonant frequency of the PLL to be lowered.

REFERENCES:
patent: 4500857 (1985-02-01), Bosselaers et al.
patent: 4745372 (1988-05-01), Miwa

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