EMI specifics of design with multiple DC-DC converters sharing common power bus

Modern circuits on boards in computing equipment are powered by very low voltages, to achieve faster speeds by reducing transition times between low and high trigger levels in logic devices. Complex ASIC components often run at 1.5 V-1.8 V; the combination of power consumption at low voltage and fast operating speed results in demands for a substantial current. Power for these devices cannot be delivered from a remote, central-to-system location - the losses in cables and connectors prohibit such an approach due to DC voltage drops. In addition, fast changes in current demand require the power source to be located close to the load, to minimize the impact of the impedance of the power bus. Step-down type DC-DC converters exhibit discontinuous pulsed input current, resulting in noise propagating through the power planes. The paper addresses the causes of the noise generated by the so-called reflected input ripple current, the effective method of suppressing it using a common-mode filtering scheme, and the compatibility of multiple DC-DC on-board converters powered by a single input bus.