3D clock distribution using vertically/horizontally-coupled resonators

Clock distribution with low skew, low jitter, and low power for high-performance microprocessors is a significant design challenge. Although traditional H-tree clock distribution circuits are widely used, the clock skew of such circuits is increased by the PVT variations associated with device scaling [1]. In recent years, there has thus been a growing interest in resonant clock distribution schemes for reduced clock skew. In particular, coupled ring oscillators with shorted outputs [2] can reduce skew and jitter without additional layout area compared to LC resonators [3]. The difference in phase and frequency of each oscillator (due to PVT variations) is equalized by the mutual connection between the oscillators. Power dissipation can also be reduced, as the enhanced variability tolerance may permit operation at lower voltages.