Synthesis of Clock Networks with a Mode Reconfigurable Topology and No Short Circuit Current

Abstract

Circuits deployed in the Internet of Things operate in low and high performance modes to cater to variable frequency and power requirements. Consequently, the clock networks for such circuits must be synthesized meeting drastically different timing constraints under variations in the different modes. The overall power consumption and robustness to variations of a clock network is determined by the topology. However, state-of-the-art clock networks use the same topology in every mode, despite that the timing constraints in the low and high performance modes are very different. In this paper, we propose a clock network with a mode reconfigurable topology (MRT) for circuits with positive-edge triggered sequential elements. In high performance modes, the required robustness to variations is provided by reconfiguring the MRT structure into a near-tree. In low performance modes, the MRT structure is reconfigured into a tree to save power. Non-tree (or near-tree) structures provide robustness to variations by appropriately constructing multiple alternative paths from the clock source to the clock sinks, which neutralizes the negative impact of variations. In MRT structures, OR-gates are used to join multiple alternative paths into a single path. Consequently, the MRT structures consume no short circuit power because there is only one gate driving each net. Moreover, it is straightforward to reconfigure MRT structures into a tree by gating the clock signal in part of the structure. Compared with state-of-the-art near-tree structures, MRT structures have 8% lower power consumption and similar robustness to variations in high performance modes. In low performance modes, the power consumption is 16% smaller when reconfiguration is used.