25.6 A 5.25GHz Subsampling PLL with a VCO-Phase-Noise Suppression Technique

Ring-oscillator (RO)-based PLLs are preferred in many applications. These PLLs exhibit features like small area, large tuning range, and multiple output phases. However, their jitter performance is worse than that in LC-oscillator-based PLLs. Although a wider PLL bandwidth can reduce the RO phase noise, it is also limited to one-tenth of the reference frequency due to loop stability. To overcome the VCO noise, injection-locked PLLs (IL-PLLs) were proposed to extend the loop bandwidth to O.4f
_REF
but suffered from large spurious tones.