CMOS Oscillators for Clock Distribution and

Abstract—The distribution and alignment of high-frequency clocks across a wide bus of links is a significant challenge in modern computing systems. A low power clock source is demon-strated by incorporating a buffer into a cross-coupled oscillator. Because the load is isolated from the tank, the oscillator can directly drive 50-Ohm impedances or large capacitive loads with no additional buffering. Using this topology, a quadrature VCO (QVCO) is implemented in 0.13 m digital CMOS. The QVCO oscillates at 20 GHz, consumes 20 mW and provides 12 % tuning range. The measured phase noise is dBc Hz @ 1 MHz frequency offset. A clock alignment technique based upon injec-tion-locked quadrature-LC or ring oscillators is then proposed. Although injection-locked oscillators (ILOs) are known to be capable of deskewing and jitter filtering clocks, a study of both LC and ring ILOs indicates significant variation in their jitter tracking bandwidth when used to provide large phase shifts. By selectively injecting different phases of a quadrature-LC or ring VCO, this problem is obviated resulting in reduced phase noise. The technique is demonstrated using a LC QVCO at 20 GHz while burning only 20 mW of power and providing an 8 dB improvement in phase noise. A ring oscillator deskews a 2 to 7 GHz clock while consuming 14 mW in 90 nm CMOS. Index Terms—Clock deskew, injection locking, jitter filtering, Q-VCO, ring oscillator. I