Automotive Electromagnetic Compatibility - Prediction and Analysis of Parasitic Components in Conductor Layouts
Sammanfattning: The electronics in the automotive industry is facing a new era where safety critical functions are electrified, as for example drive-by-wire technology. At the same time as the number of electrical loads in the vehicles is increasing, the time to market is decreasing. Full scale prototypes of a vehicle are often only available at a late stage in the development process where changes are rather costly. This implies that prediction and simulation of a system are of importance and are useful already at an early stage of the development process. There are economic benefits that can be gained by prediction and simulation of the system such as: reduction of time to market, virtual tests, virtual prototypes and optimization of electronic circuits with respect to safety margins of filters. The high number of electrical loads in the vehicle leads to different cable harnesses routed along the body and chassis of the vehicle. These cable harnesses will contain both power conductors and communication conductors, routed close together. When conductors are routed close to each other, a signal on one conductor can interfere with the signal on another conductor. This phenomenon is called crosstalk. Crosstalk can increase the noise levels, create unplanned spikes or destroy data on nearby conductors. Hence it should always be a prime suspect in an electromagnetic interference investigation or a candidate for prediction. Crosstalk between two conductors is coupled by the mutual inductance and capacitance. When these parameters are known, the crosstalk can be estimated by using a circuit simulation. The mutual inductance and capacitance between the conductors as well as the self inductance and capacitance of each conductor depend on the surrounding environment. This implies that the conductor layout is an important factor when it comes to designing a system that is robust against crosstalk. This thesis focuses on estimation of the parasitic components in a system with two conductors and a ground structure. Since the parasitic components are affected by the conductor layout, five different layouts are investigated. The parameters are estimated by using analytical calculations, electromagnetic simulations with the software CableMod and measurements. An approximate method for fast analytical calculations is proposed and evaluated. The parameter values estimated with the different methods are compared in the thesis. The values yielded from the accurate analytical calculation and the simulations agree well. Some of the measured values deviate from the theoretical values, and it is shown that the differences emanate from the fact that the theoretical models do not exactly describe the measurement setup. The different parameter setups from the different estimation methods and the investigated conductor layouts are employed in circuit simulations in the software LTSpice/ Switchercad III. The circuit simulations show that the proposed approximate analytical calculation method is sufficient to use for prediction of crosstalk and comparison between different conductor layouts.
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