The Conical-Fishbone Clock Tree: A Clock-Distribution Network for a Heterogeneous Chip Multiprocessor AI Chiplet

Abstract

In this paper we present a clock tree network that is inspired by the shape of an inverted cone. Conical sections are created in the inverted cone, and each of these resulting rings is considered to be one of the many nets in a Fishbone clock tree. When a ring is excited at uniform intervals from the ring below, the symmetry in the circular characteristics of the wire will make the effect of reflections be exactly the same along any place in the wire. The proposed clock tree named Conical-Fishbone clock tree allows ultra-low clock skew while offering the modularity to support a hierarchical design using standard CAD flows. The Conical-Fishbone tree network is employed in the L1- NOC, the L2-NOC and the DDR DRAM PHY of the core (17.47 mm X 14.13 mm) “chiplet” in the 2.5D nano-Abacus SOC currently being fabricated in the Global Foundries 55nm CMOS technology.