PLL LOOP FILTER WITH SWITCHED-CAPACITOR RESISTOR

摘要

A phase-locked loop circuit having improved phase noise characteristics includes a voltage-controlled oscillator (12) developing an oscillating output signal responsive to a voltage control input. A reference source provides a reference frequency signal. A phase detector (30) is 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 (46) connects the phase detector output to the voltage control input. The loop filter includes a switched-capacitor equivalent resistor (Q1, Q2, CR).