| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To reduce a capacitance value of a capacitor for a temperature-compensation loop filter. <P>SOLUTION: A PLL synthesizer comprises: a phase comparator PD; a loop filter LF; and a voltage-controlled oscillator VCO. In addition, as a temperature-compensation loop, the PLL synthesizer comprises: a comparator CMP that outputs a comparison signal 30 when a frequency control voltage goes out of a control voltage range; a digital filter DF that integrates the comparison signal 30 to generate an M-bit first digital signal 32;ΣΔmodulators 12 and 10 that input the first digital signal 32 and generate a second digital signal 34 corresponding to the first digital signal 32 as an N-bit signal (where N is smaller than M); a temperature-compensation charge pump CPt that converts the second digital signal 34 to a current signal 36; and a temperature-compensation loop filter TF that converts the current signal 36 to a temperature-compensation control voltage. The voltage-controlled oscillator VCO controls a frequency of an output clock CKout based on the temperature-compensation control voltage ft. <P>COPYRIGHT: (C)2012,JPO&INPIT</p> |
