Oscillators – Automatic frequency stabilization using a phase or frequency... – With intermittent comparison controls
Patent
1996-12-11
1998-11-10
Grimm, Siegfried H.
Oscillators
Automatic frequency stabilization using a phase or frequency...
With intermittent comparison controls
331 1A, 331 8, 331 17, 331 25, H03L 7093
Patent
active
058360000
ABSTRACT:
The capture range and stability of a phase locked loop are improved by adjusting the free running frequency of a voltage controlled oscillator in response to the output signal of the phase locked loop. The output signal is filtered and amplified, and then compared to a reference signal from the voltage controlled oscillator which is indicative of the free running frequency. A direct current level capture circuit compares the filtered and amplified output signal with the reference signal and generates a control signal which adjusts the free running frequency so as to equalize the output signal and the reference signal. The control signal is generated by sequentially and consecutively enabling a series of filter reset circuits. A switch control circuit controls two feedback paths between the phase detector and the voltage controlled oscillator. The first feedback path includes a low pass filter and is selected by the switch circuit for normal operation. During capture operation, the second feedback path, which includes a low pass filter in series with a DC level converter, is selected. The switch circuit is controlled by a switch select signal which is generated by the direct current level capture circuit.
REFERENCES:
patent: 4633488 (1986-12-01), Shaw
patent: 5382922 (1995-01-01), Gersbach et al.
Grimm Siegfried H.
Samsung Electronics Co,. Ltd.
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