ADAPTIVE BANDWIDTH PHASE LOCKED LOOP WITH FEEDFORWARD DIVIDER

摘要

An adaptive bandwidth phase locked loop with a feedforward driver is provided to increase a tracking jitter as a bandwidth is decreased since VCO(Voltage Controlled Oscillator) phase noise dominates an output jitter in a measurement setup, the tracking jitter increased as the bandwidth decreased. An adaptive bandwidth phase locked loop with a feedforward driver includes a phase frequency detector(PFD)(10), a charge pump (CP)/loop filter(LF)(16) and output frequency control circuit(20) including a voltage control oscillator(VCO)(22) and a feedforward frequency divider(FF Div)(24) with a division factor of N, and a feedback frequency divider(FB Div)(28) with a division factor of M. The VCO provides a VCO signal with a frequency fVCO. The FF Div provides an output clock signal(out clk) with a frequency fOUT which is also provided to the FB Div. The output of the FB Div is provided as an input to PFD(14). A charge pump and a loop filter of the CP/LF are different circuits but for convenience of illustration are combined. The division factor(N) of the FF Div is adjusted. In some embodiments, this adjustment allows the FF Div to generate a wide range of frequencies even if the VCO tuning range is relatively narrow.