Isodelay output driver design using step-wise charging for low power

As the technology is scaling, the on-chip supply voltage is also reducing. However, off-chip communication voltage has failed to keep-up with this trend. The main reason for this is that the ICs in a system are designed by various design houses and in different technologies which require standardized communication interfaces. We present an output driver using energy recycling to communicate with another chip operating at a different/higher voltage through a standardized interface. Charge recycling is performed without any performance penalty. Various circuits, designed for implementing the control circuitry for achieving the charge recovery using step-wise charging, are discussed. The simulation results show that step-wise charging technique is very useful for output drivers driving large loads in the range of 10pF to 30pF. The power savings range from 22% to 35% without much degradation in performance. In fact, performance is improved for most of the cases depending upon the size of the recycling switch used. Furthermore, re-using the charge-recovery current in a DC-DC converter is possible, if certain conditions, as discussed in the paper, are met.