Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By phase
Reexamination Certificate
1999-08-25
2001-07-03
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By phase
C327S003000, C327S047000, C327S156000, C327S147000
Reexamination Certificate
active
06255858
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phase-frequency detector which detects a frequency error between two signals from a temporal change in a phase error signal representing the phase difference between the two signals corrects the phase error signal, and outputs the corrected phase error signal, and a phase-locked loop circuit incorporating the phase-frequency detector.
2. Description of the Related Art
A phase-locked loop (PLL) circuit is used to recover a carrier from an intermediate frequency (IF) signal. In this case a baseband signal consisting of an I-phase signal and a Q-phase signal is generated by multiplying the input IF signal by two recovered quadrature carriers. These component signals are converted by A/D converters into digital signals and the values of the I-phase and Q-phase signals are fed as addresses to a ROM where the value of tan
−1
(Q/I) is stored, to generate the phase error signal related to the phase difference between the input signal and the recovered carrier. The frequency of the recovered carrier is controlled by the phase error signal thus generated and whose high-frequency component has been removed by a low-pass filter.
The phase error signal generated as described above varies periodically within the range of ±180° because of the periodicity of the function tan
−1
. Accordingly, if the frequency of the input signal is far from that of the recovered carrier there arises the problem that synchronization cannot be established or the time required to establish synchronization becomes extremely long.
SUMMARY OF THE INVENTION
It is accordingly, an object of the present invention to provide a phase-frequency detector for generating a frequency-phase error signal taking account of the frequency difference as well as the phase difference between two signals, and a phase-locked loop circuit incorporating the phase-frequency detector and capable of establishing synchronization in a short period of time even when the two signals are far from each other in frequency.
According to the present invention there is provided a phase-frequency detector comprising: a frequency error detector which detects and outputs a frequency error between two signals based on a change in a phase error signal representing a phase error between the two signals; and a signal corrector which corrects the phase error signal based on the output of the frequency error detector, and outputs the corrected phase error signal as a frequency-phase error signal.
According to the present invention there is also provided a phase-locked loop circuit comprising: a phase comparator which compares the phase of an input signal with the phase of a signal output from an oscillator, and outputs a phase error signal representing a phase error between the two signals; a phase-frequency detector including a frequency error detector which detects and outputs a frequency error between the two signals, based on a change in the phase error signal, and a signal corrector which corrects the phase error signal based on the output of the frequency error detector, and outputs the corrected phase error signal as a frequency-phase error signal; a low-pass filter which passes therethrough only a low-frequency component contained in the frequency-phase error signal; and the oscillator which outputs a signal of a frequency corresponding to the output of the low-pass filter.
REFERENCES:
patent: 5079512 (1992-01-01), Muto
Akiyama Chiyoshi
Kawasaki Toshio
Fujitsu Limited
Helfgott & Karas P.C.
Le Dinh T.
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