A Contribution to Enhanced EMC Immunity Analysis of Automotive Smart-Power ICs into the GHz Region

In the last decades, sophisticated electronic components with steadily rising density and complexity have mainly driven the innovations in the automotive industry. With this evolution, the harmful influence of EMI (Electromagnetic Interference) has grown, so that the prevention of EMC (Electromagnetic Compatibility) related failures has become a major concern. Due to this extensive use of car electronics, automotive ICs (Integrated Circuit) have to operate in an increasingly harsh environment. Particularly, they are susceptible to electromagnetic disturbances emanating from off-board and on-board sources which propagate trough the vehicle harness and impair their functionality.

To evaluate the susceptibility of ICs to conducted EMI up to 1GHz, the DPI (Direct Power Injection) is the most relevant method. The standard specifies an ideal 50 O environment for the investigations and an upper frequency limit of 1GHz. However, this constant load assumption is usually not fulfilled in the IC final environment, were IC terminals are subjected to a wide range of impedances, principally dependent on surrounding circuits or interacting ECUs (Electronic Control Unit), PCB traces, cable nature and dimensions, etc. Hence, the expected influence of this load alteration on the susceptibility of ICs, which is particularly relevant for IC pins heading outside the ECU, can’t be analyzed by means of the DPI-test alone. Moreover, with the proliferation of wireless and mobile communication networks, also investigation of frequencies above 1GHz is more than relevant.

In the framework of this thesis, a novel technique capable of taking into account all possible load impedance conditions during susceptibility investigations has been implemented: the variable-load DPI method. For the first time, the load-pull technique, well-known from RF-amplifier design and large-signal transistor characterization, is brought into the field of EMC in order to reasonably cover all later applications and stages of the EMC qualification chain from an impedance point of view. In addition to this, with the intent of accelerating and simplifying EMC immunity simulations of ICs in a non-50 O environment, two small-signal approximate approaches are implemented. These new methods have been applied and successfully validated against measurements up to 4GHz for four essential automotive analog circuits processed in state-of-the art smart-power technologies, namely a low-side driver, a high-side driver, a cascode current mirror and an ESD-protection. In this regard, the underlying EMI-triggered effects have been discussed and remedial measures to increase the robustness proposed. The variable-load DPI results clearly show a significant deviation from the standard-DPI estimations under worst-case conditions. For the case of EMI-coupling trough a twisted pair as an example, the discrepancy caused by real-world EMC threats is of the order of 10dB in the frequency range from 30MHz to 300MHz.