| 摘要 |
PURPOSE: A phase locked loop circuit of a semiconductor device is provided to improve lock time and noise characteristics by varying a resistance value of a loop filter in a reciprocal relation to a current amount which is adjusted through a charge pump according to a phase difference. CONSTITUTION: A phase locked loop circuit of a semiconductor device comprises a phase detector(100) which detects a difference between a reference signal(Vref) having a predetermined frequency and a divided signal(Vdiv) from a divider(600) and generates up and down signals(UP,DOWN) as a detection result. A charge pump(200) charges and discharges a loop filter(300) according to the up and down signals(UP,DOWN) and control signals(CON1,CON2,CON3) from a control circuit(400). The loop filter(300) has a pair of capacitors and a variable resistor. The variable resistor of the loop filter(300) is varied according to according to the control signal(CON3) so as to adjust a band width of an output signal(Vfout) from a voltage controlled oscillator(500). The control circuit(400) generates the control signals(CON1,CON2,CON3) in response to the up and down signals(UP,DOWN).
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