Patent ID: 6420917
Filing Date: 2002-07-16
Classification: H03L

Abstract:
A phase-locked loop circuit comprising:a voltage-controlled oscillator developing an oscillating output signal responsive to a voltage control input; a reference source providing a reference frequency signal; a phase detector operatively connected to the voltage-controlled oscillator and the reference source developing an output proportional to a phase difference between the oscillating output signal and the reference frequency signal; a loop filter connecting the phase detector output to the voltage control input, the loop filter comprising: a first shunt capacitor connected to the output of the phase detector; a switched capacitor; and a switching circuit to alternately connect said switched capacitor in series to the first shunt capacitor when the switching circuit is in a first state and to ground when the switching circuit is in a second state such that the switched capacitor functions as a resistive element in said loop filter.