Frequency synthesizer PLL having digital and analog phase detect

Details Frequency synthesizer PLL having digital and analog phase detect Frequency synthesizer PLL having digital and analog phase detect

1990-10-29

1991-10-15

Grimm, Siegfried H.

Oscillators

Automatic frequency stabilization using a phase or frequency...

Afc with logic elements

331 11, 331 14, 331 17, 331 27, 331DIG2, 307516, 328134, H03L 7087, H03L 7091, H03L 7095

Patent

active

050577930

ABSTRACT:
A frequency synthesizer phase locked loop includes a voltage controlled oscillator (VCO) providing a variable frequency signal, a reference frequency oscillator providing a reference frequency signal, a phase comparison circuit for comparing the phases of the variable frequency and reference frequency signals and providing an output signal to a loop filter, the output of the loop filter providing a frequency control signal to the VCO. The phase comparison circuit includes a digital phase detector providing an output signal on an output line coupled to a charge pump for providing a first output signal to the loop filter; and an analog phase detector including a sample and hold circuit, and a control circuit responsive to the variable and reference frequency signals for providing a signal for sampling to the sample and hold circuit, the sample and hold circuit providing a second output signal to the loop filter. The analog phase detector includes a voltage detection circuit for detecting the voltage level of the signal held by the sample and hold circuit, and for selectively inhibiting the first output signal when the voltage is within predetermined limits.

REFERENCES:
patent: 4107623 (1978-08-01), Graf et al.
patent: 4167711 (1979-09-01), Smoot
patent: 4490688 (1984-12-01), Borras et al.
patent: 4803705 (1989-02-01), Gillingham et al.

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