Noise aware decoupling capacitors for multi-voltage power distribution systems

Multiple power supply voltages are often used in modern high performance ICs, such as microprocessors, to decrease power consumption without affecting circuit speed. The system of decoupling capacitors used in power distribution systems with multiple power supplies is described. In order to minimize the total impedance of a multi-voltage power delivery system as seen from a particular power supply, a decoupling capacitor is placed between the power supplies. The noise at one power supply can couple into the other power supply, causing power and signal integrity problems in the overall system. With the introduction of a second power supply, therefore, the interaction between the two power distribution networks should be considered. The dependence of the magnitude of the voltage transfer function on the parameters of the power distribution system is investigated. It is shown that it is highly desirable to maintain the effective series inductance of the decoupling capacitors as low as possible to decrease the overshoot in the response of a dual voltage power distribution system over a wide range of operating frequencies. A criterion for an overshoot-free voltage response is presented. It is noted that the frequency range of the overshoot-free voltage response can be traded off with the magnitude of the response.