A Novel Method of Active Power Noise Cancellation in I/O Buffers

This paper presents a scheme to reduce the on-die voltage noise that occurs due a buffer switching event. Both output and input buffer switch events are addressed. A generic power delivery network (PDN) model with parasitic inductance is assumed. A change in current ( ${rm di}/{rm dt}$) across the inductor is considered the primary cause of the voltage noise. On-die decoupling capacitance is traditionally added to the power delivery network to address this problem and to limit the droop. The method described in the paper shows a principally different approach. The maximum ${rm di}/{rm dt}$ is managed to reduce the voltage noise. It is proposed to send to a buffer a current waveform from an external supply or to recycle charge from a locally charged capacitance when the ${rm di}/{rm dt}$ occurs, thus substantially reducing the on-die voltage noise. Alternatively, at a given acceptable level of voltage noise the on-die capacitance can be reduced, providing significantly lower product cost. This paper provides theoretical and modeling background of the proposed schemes and includes simulation results on several performance characteristics.