A Low Energy Clock Network with a Huge Number of Local Synchronized Oscillators

A clock system for a huge grid of small clock regions is presented. There is an oscillator in each clock region, which drives the local clock of a processing element (PE). The oscillators are kept synchronized by exploiting the phase of their neighbors. In an infinite mesh, the clock skew would be zero, but in a network of limited size there will be fringe effects. In a mesh with 25×25 oscillators, the maximum skew between neighboring regions is within 3.3 ps. By slightly adjusting the free running frequency of the oscillators, this skew can be reduced to 1.2 ps. The mesh may contain millions of clock regions.

Because there is no central clock, both power consumption and clock frequency can be improved compared to a conventional clock distribution network. A PE of 150×150 µm² running at 6.7 GHz with 93 master-slave flip-flops is used as an example. The PE-internal clock skew is less than 2.3 ps, and the energy consumption of the clock system 807 µW per PE. It corresponds to an effective gate and wire capacitance of 509 aF, or 7.3 gate capacitances.

Power noise is reduced by scheduling the local oscillators gradually along one of the grid’s axes. In this way, surge currents, which generally have their peaks at the clock edges, are distributed evenly over a full clock cycle.