SPREAD SPECTRUM CONTROL PLL CIRCUIT AND ITS START-UP METHOD
First Claim
Patent Images
1. A spread spectrum control PLL circuit for outputting a spread spectrum clock signal based on an input reference clock signal, comprising:
- a charge pump circuit configured to switch charging and discharging of a charging current, depending on a phase difference between a feedback clock signal based on an output clock signal of the PLL circuit and the reference clock signal;
a loop filter circuit having a filter capacitor which is charged and discharged using the charging current output from the charge pump circuit;
a voltage controlled oscillator configured to oscillate at a frequency depending on an input control voltage; and
a calibration circuit configured to adjust at least one of one of the charging current of the charge pump circuit and a capacitance value of the filter capacitor and a gain of the voltage controlled oscillator, depending on a frequency of the reference clock signal.
1 Assignment
0 Petitions
Accused Products
Abstract
A calibration circuit (19) adjusts at least one of one of a charging current of a charge pump circuit (12) and a capacitance value of a filter capacitor in a loop filter circuit (13) and a gain of a voltage controlled oscillator (14), depending on a frequency of a reference clock signal input to a calibration circuit (10).
49 Citations
19 Claims
-
1. A spread spectrum control PLL circuit for outputting a spread spectrum clock signal based on an input reference clock signal, comprising:
-
a charge pump circuit configured to switch charging and discharging of a charging current, depending on a phase difference between a feedback clock signal based on an output clock signal of the PLL circuit and the reference clock signal; a loop filter circuit having a filter capacitor which is charged and discharged using the charging current output from the charge pump circuit; a voltage controlled oscillator configured to oscillate at a frequency depending on an input control voltage; and a calibration circuit configured to adjust at least one of one of the charging current of the charge pump circuit and a capacitance value of the filter capacitor and a gain of the voltage controlled oscillator, depending on a frequency of the reference clock signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
-
Specification