Multi-phase charge sharing method and apparatus

Abstract

A multi-phase charge sharing technique for electrical and electronic circuits. During a first phase, I/O drivers for circuit outputs that are to change value are deactivated. During a second phase, a plurality of circuit outputs are connected together to allow for charge transfer between higher voltage outputs and lower voltage outputs. Since the output nodes generally have capacitive loads, the common connection of high voltage nodes with low voltage nodes results in charge equilibrium, where the voltage on each commonly connected node acquires the same voltage. As existing charge from high voltage nodes is being used to charge lower voltage nodes, the lower voltage nodes are partially charged without requiring additional external power. Following this charge transfer, the outputs are disconnected from one another and operated in their normal fashion. Thus, output values that are changing from a low to a relatively higher voltage are partially boosted to a higher voltage level from existing high voltage sources on other circuit outputs. This reduces the amount of power which is required to drive the output node to a subsequent voltage level. Similarly, output values that are changing from a high to a relatively lower voltage are partially discharged by existing low voltage output nodes. The partial discharging of these nodes results in a reduction in ground bounce.