Double phase locked loop circuit
AssigneeSanyo Electric Co., Ltd.
InventorsHideo Imaizumi, Yoshiaki Takahashi
Life of this patent
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Abstract
A frequency of a first VCO (12) for generating a carrier of a video IF signal is set by using a frequency of a second VCO (15) as reference. The oscillation frequency of the second VCO (15) is controlled in response to the phase difference between an output signal of the first VCO (12) and the video IF signal. As a result, the output signal phase of the first VCO (12) is adjusted, and the output signal is locked to a carrier frequency of the video IF signal. Thus, the oscillation frequency of the first VCO (12) can be set automatically. Further, a signal for the phase difference between the output signal of the first VCO (12) and the video IF signal is also applied to the first VCO (12), thereby improving the stability of circuit operation.
Claims14
A PLL circuit comprising:
- a first VCO (voltage controlled oscillator) which oscillates at substantially the same frequency as an input signal;
- a first phase comparator which compares a phase of an oscillation output signal from said first VCO with a phase of said input signal for outputting a signal for a phase difference therebetween;
- a first loop filter for smoothing the output signal of said first phase comparator;
- a second VCO whose oscillation frequency is changed in response to an output signal of said first loop filter, said second VCO having a high frequency selectivity compared with said first VCO and oscillating at a frequency lower than said first VCO;
- a dividing circuit which divides the oscillation output signal of said first VCO for generating substantially the same low frequency signal as said second VCO;
- a second phase comparator which compares a phase of said dividing circuit with a phase of an oscillation output signal of said second VCO for outputting a signal for a phase difference therebetween;
- and
- a second loop filter for smoothing an output signal of said second phase comparator and feeding a signal to control the oscillation frequency of said first VCO into said first VCO.
Dependencies are inferred from the claim text.