PLL frequency modulator having bias voltage applied to filter ca

Details PLL frequency modulator having bias voltage applied to filter ca PLL frequency modulator having bias voltage applied to filter ca

1990-09-17

1991-09-03

Grimm, Siegfried H.

Modulators

Frequency modulator

Including stabilization or alternatively distortion, noise...

331 17, 332135, 455113, 455119, H03C 309, H03L 7093

Patent

active

050458183

ABSTRACT:
A frequency modulation circuit includes a VCO which constitutes a PLL along with a loop filter which is operated by a current source. Such a frequency modulation circuit is formed in monolithic IC. When a power source of the IC is turned-on, a capacitor included in the loop filter is biased by an output voltage of a voltage follower which receives Vcc/2. Since this output voltage rises in the same manner as Vcc, a center frequency of the VCO can be rapidly pulled into a phase-locked state of the PLL. In addition, the frequency modulation circuit is provided with a voltage-to-current conversion circuit which increases a charging current for the capacitor in response to a mute signal generated when the power source is turned-on, whereby the time constant of the loop filter is decreased substantially.

REFERENCES:
patent: 4117422 (1978-09-01), Hunt

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