| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a loop filter in which a capacitance ratio of capacitors comprising a secondary or higher-order filter can be reduced to allow an on-chip state. <P>SOLUTION: There are provided two charge pump circuits for charging and discharging filter capacitance in response to signals generated by a phase comparator circuit (236). Current values of current sources (I11, I12) comprising one of the charge pump circuits are made smaller than those of current sources (I21, I22) comprising the other charge pump circuit. The loop filter comprises two capacitive elements of a first capacitive element (C2) connected to a charge/discharge node and a second capacitive element (C1) connected to the charge/discharge node through a resistive element (R). The first capacitive element is charged and discharged by the one charge pump circuit, while the second capacitive element is charged and discharged by the other charge pump circuit. Thus, a charging current source of the one charge pump circuit operates simultaneously with a discharging current source of the other charge pump circuit, i.e., the two charge pump circuits operate in opposite phase. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
