A multi-level transmission line network approach for multi-giga hertz clock distribution

In high performance systems, process variations and fluctuations of operating environments have significant impact on the clock skew. Recently, hybrid structures of H-tree and mesh were proposed to distribute the clock signal with a balanced H-tree and lock the skew using the shunt effect of the mesh. However, in multi-giga hertz regime, the RC model (Orshansky et al., 2002) of the mesh is no longer valid. The inductance effect of the mesh can even make the skew worse. In this paper, we investigate the use of a novel architecture which incorporates multiple level transmission line shunts to distribute global clock signal. We derive the analytical expression of the skew reduction contributed by the shunt of a transmission line with the length of an integral multiple of clock wavelength. Based on the analytical skew expression, we adopt convex programming techniques to optimize the wire widths of the multi-level transmission line network. Simulation results show that the multilevel network achieves below 4ps skew for 10GHz clock rate.

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