A 4.2 GHz PLL Frequency Synthesizer with an Adaptively Tuned Coarse Loop
This paper describes a self-tuning 3/sup rd/ order type III phase-locked-loop (PLL) with the frequency control implemented in 3 parallel paths. The crucial elements that allow frequency response tracking are a triple control voltage controlled oscillator (VCO), a frequency to current (F2I) converter, and a switched capacitor loop filter. Near constant VCO gain over process variations, in addition to compensation for feedback ratio variation, near constant F2I gain over process variations and switched cap filters synchronized to the reference allows tailoring the open loop frequency response to track the reference. A high speed locking technique is employed which significantly reduces acquisition time in low bandwidth cases. This PLL was fabricated in a 0.18/spl mu/m CMOS logic process.