| 摘要 |
<p>A phase-locked loop circuit comprises a voltage-controlled oscillator, a phase comparator, a low-pass filter (15), a plurality of pump circuits (14S, 14F, ... ), and a selecting circuit (G45) for selecting one of the pump circuits. The low-pass filter is comprised of a capacitor (C) and a plurality of resistors (R1, R2) each connected to one of the pump circuits. By selecting one of the pump circuits to connect to a corresponding resistor, the cutoff frequency or time constant of the low-pass filter is switched in multi-steps.</p> |
