Synchronous circuit capable of properly removing in-phase noise
First Claim
1. A synchronous circuit comprising:
- a phase comparator for comparing a feedback signal with an input reference signal to detect a phase difference and for outputting a phase difference signal corresponding to the phase difference;
a charge pump for outputting charge/discharge signals on the basis of the phase difference signal output from said phase comparator;
a low-pass filter for changing a charge amount accumulated in a capacitor on the basis of the charge/discharge signals output from said charge pump and for outputting control signals corresponding to the charge amount as differential signals;
a voltage-controlled oscillator for changing an oscillation frequency of an output on the basis of the control signals output from said low-pass filter;
a frequency divider for dividing the output from said voltage-controlled oscillator in order to output the feedback signal;
intermediate value generation means for generating an intermediate value between the control signals output from said low-pass filter;
a comparator for comparing the intermediate value output from said intermediate value generation means with an externally input reference value and for outputting a comparison result; and
control means for receiving the comparison result output by said comparator and for controlling levels of the charge/discharge signals output from said charge pump so that the intermediate value is made to match the externally input reference value.
1 Assignment
0 Petitions
Accused Products
Abstract
The synchronous circuit has: a phase comparator for comparing a feedback signal with an input reference signal to detect a phase difference and outputting a phase difference signal corresponding to the phase difference; a charge pump for outputting charge/discharge signals on the basis of the phase difference signal output from said phase comparator; a low-pass filter for changing a charge amount accumulated in a capacitor on the basis of the charge/discharge signals output from said charge pump and outputting control signals corresponding to the charge amount as differential signals; a voltage-controlled oscillator for changing an oscillation frequency of an output on the basis of the control signals output from said low-pass filter; a frequency divider for multiplying the output from said voltage-controlled oscillator and outputting the feedback signal; and fixing means arranged on an output side of said charge pump and operated, when the phase difference between the reference signal and the feedback signal is near a dead band of said phase comparator, such that levels of the charge/discharge signals output from said charge pump are fixed at predetermined levels. According to the synchronous circuit, troubles causes by the unbalance in charge/discharge operation performed by the change pump can be prevented.
73 Citations
12 Claims
-
1. A synchronous circuit comprising:
-
a phase comparator for comparing a feedback signal with an input reference signal to detect a phase difference and for outputting a phase difference signal corresponding to the phase difference; a charge pump for outputting charge/discharge signals on the basis of the phase difference signal output from said phase comparator; a low-pass filter for changing a charge amount accumulated in a capacitor on the basis of the charge/discharge signals output from said charge pump and for outputting control signals corresponding to the charge amount as differential signals; a voltage-controlled oscillator for changing an oscillation frequency of an output on the basis of the control signals output from said low-pass filter; a frequency divider for dividing the output from said voltage-controlled oscillator in order to output the feedback signal; intermediate value generation means for generating an intermediate value between the control signals output from said low-pass filter; a comparator for comparing the intermediate value output from said intermediate value generation means with an externally input reference value and for outputting a comparison result; and control means for receiving the comparison result output by said comparator and for controlling levels of the charge/discharge signals output from said charge pump so that the intermediate value is made to match the externally input reference value. - View Dependent Claims (2, 3)
-
-
4. A synchronous circuit comprising:
-
a phase comparator for comparing a feedback signal with an input reference signal to detect a phase difference and for outputting a phase difference signal corresponding to the phase difference; a charge pump for outputting charge/discharge signals on the basis of the phase difference signal output from said phase comparator; a low-pass filter for changing a charge amount accumulated in a capacitor on the basis of the charge/discharge signals output from said charge pump and for outputting control signals corresponding to the charge amount as differential signals; a voltage-controlled oscillator for changing an oscillation frequency of an output on the basis of the control signals output from said low-pass filter; a frequency divider for dividing the output from said voltage-controlled oscillator in order to output the feedback signal; intermediate value generation means for generating an intermediate value between the control signals output from said low-pass filter; a comparator for comparing the intermediate value output from said intermediate value generation means with an externally input reference value and for outputting a comparison result; and control means for receiving the comparison result output by said comparator and for controlling levels of the control signals output from said low-pass filter so that the intermediate value is made to match the externally input reference value. - View Dependent Claims (5, 6)
-
-
7. A synchronous circuit comprising:
-
a phase comparator for comparing a feedback signal with an input reference signal to detect a phase difference and for outputting a phase difference signal corresponding to the phase difference; a charge pump for outputting charge/discharge signals on the basis of the phase difference signal output from said phase comparator; a low-pass filter for changing a charge amount accumulated in a capacitor on the basis of the charge/discharge signals output from said charge pump and for outputting control signals corresponding to the charge amount as differential signals; a voltage-controlled oscillator for changing an oscillation frequency of an output on the basis of the control signals output from said low-pass filter; a frequency divider for dividing the output from said voltage-controlled oscillator in order to output the feedback signal; intermediate value generation means for generating an intermediate value between the charge/discharge signals output from said charge pump; a comparator for comparing the intermediate value output from said intermediate value generation means with an externally input reference value and for outputting a comparison result; and control means for receiving the comparison result output by said comparator and for controlling levels of the charge/discharge signals output from said charge pump so that the intermediate value is made to match the externally input reference value. - View Dependent Claims (8, 9)
-
-
10. A synchronous circuit comprising:
-
a phase comparator; a charge pump circuit connected to said phase comparator; a low-pass filter connected to said charge pump circuit; a voltage-level fixing circuit connected to at least one of an output of said charge pump circuit and an output of said low-pass filter; a voltage-controlled oscillator connected to said low-pass filter; and a frequency divider connected to said voltage-controlled oscillator, wherein said charge pump circuit outputs first and second signals on first and second output lines, said low-pass filter outputs third and fourth signals on third and fourth output lines, and said voltage-level fixing circuit includes; an intermediate voltage generating circuit connected to said third and fourth output lines; a comparator having a first input connected to said intermediate voltage generating circuit and a second input connected to a reference voltage; a first switch circuit having an input connected to an output of said comparator and an output connected to said first output line of said charge pump circuit; and a second switch circuit having an input connected to said output of said comparator and an output connected to said second output line of said charge pump circuit.
-
-
11. A synchronous circuit comprising:
-
a phase comparator; a charge pump circuit connected to said phase comparator; a low-pass filter connected to said charge pump circuit, a voltage-level fixing circuit connected to at least one of an output of said charge pump circuit and an output of said low-pass filter; a voltage-controlled oscillator connected to said low-pass filter; and a frequency divider connected to said voltage-controlled oscillator, wherein said low-pass filter outputs first and second signals on first and second output lines, and said voltage-level fixing circuit includes; an intermediate voltage generating circuit connected to said first and second output lines; a comparator having a first input connected to said intermediate voltage generating circuit and a second input connected to a reference voltage; a first switch circuit having an input connected to an output of said comparator and an output connected to said first output line of said low-pass filter; and a second switch circuit having an input connected to said output of said comparator and an output connected to said second output line of said low-pass filter.
-
-
12. A synchronous circuit comprising:
-
a phase comparator; a charge pump circuit connected to said phase comparator; a low-pass filter connected to said charge pump circuit; a voltage-level fixing circuit connected to at least one of an output of said charge pump circuit and an output of said low-pass filter; a voltage-controlled oscillator connected to said low-pass filter; and a frequency divider connected to said voltage-controlled oscillator, wherein said charge pump circuit outputs first and second signals on first and second output lines, and said voltage-level fixing circuit includes; an intermediate voltage generating circuit connected to said first and second output lines; a comparator having a first input connected to said intermediate voltage generating circuit and a second input connected to a reference voltage; a first switch circuit having an input connected to an output of said comparator and an output connected to said first output line of said charge pump circuit; and a second switch circuit having an input connected to said output of said comparator and an output connected to said second output line of said charge pump circuit.
-
Specification