Study and investigation of Active EMI filtering techniques able to minimize conducted electromagnetic emission on DC/DC converters

As electronic systems get more sophisticated, strongly heterogeneous functional blocks are required to be placed close to each other in a strictly constrained amount of space (either at board level, system-on-a-chip level, or integrated level) to fulfil the reduced requirements on the size and the costs of the desired final solution. The coexistence of such different functional blocks leads to many circuital issues. Here, the problem of electromagnetic interference (EMI) generated by a circuit and affecting nearby ones is considered. The relevance of this problem is such that, in the design of any circuit, it is mandatory to comply with a set of international regulations that limits the level of the emitted electromagnetic energy to ensure the electromagnetic compatibility (EMC) of the device with ones located in the nearby environment. Over the years, several techniques have been developed with the aim of complying with these regulations. Focusing on the conducted emission regulatory requirements (which refer to the electromagnetic energy that propagates by a direct conduction on metallic conductors’ paths), a possible solution consists in introducing EMI passive filters whose components’ values depend on the desired attenuation that allows to reduce the emission to the desired level. Of course, the introduction of additional EMI filters to the overall system is not cost-free at all, as it leads to a significant increase both in price and in board area. Therefore, an innovative and recently developed technique consists in exploiting active filters, whose working principle is remarkably analogous to the active noise control method. The working principle consists in evaluating the unwanted interference signal and simultaneously injecting an antiphase copy of it, with the aim of completely cancelling it out or, at least, reducing it. This allows to achieve the same attenuation levels with respect to the passive solution, with a smaller volume and costs that are comparable with that of a completely passive solution. In this thesis work, in collaboration with STMicroelectronics, the implementation of an active filter device for a prototype of a step-down DC/DC constant on-time power converter provided by STMicroelectronics has been investigated. The converter belongs to the class of switch mode power supply (SMPS), where the high switch voltage and fast current slew rates that occur during switching transitions cause it to be a major source of EMI. After studying the device’s conducted emission level by means of the SIMPLIS © simulation environment an active EMI filter has been designed, also exploiting MATLAB © in the preliminary phases. The design phase has been tackled taking into account the required emission levels that must be respected to comply with the regulatory requirements. The active topology impact on the overall system’s performances has been hence evaluated, and a direct comparison with respect to some typical passive topologies has been performed. The proposed solution highlights a non-negligible reduction in terms of total occupied area and costs, guaranteeing at the same time a satisfactory attenuation level of the conducted emitted disturbances.