Worst Case Power/Ground Noise Estimation Using an Equivalent Transition Time for Resonance

The nonmonotonic behavior of power/ground noise with respect to the transition time tr is investigated for an inductive power distribution network with a decoupling capacitor. The worst case power/ground noise obtained with fast switching characteristics is shown to be significantly inaccurate. An equivalent transition time that corresponds to resonance is presented to accurately estimate the worst case power/ground noise in the time domain. Furthermore, the sensitivity of the ground noise to the decoupling capacitance Cd and parasitic inductance Lg is evaluated as a function of the transition time. Increasing the decoupling capacitance is shown to efficiently reduce the noise for transition times smaller than twice the LC time constant, tr les 2radic(LgCd). Alternatively, reducing the parasitic inductance Lg is shown to be effective for transition times greater than twice the LC time constant, tr ges 2radic(LgCd). The peak noise occurs when the transition time is approximately equal to twice the LC time constant, tr ap 2radic(LgCd) , referred to as the equivalent transition time for resonance.