The aim of the master's thesis was to design an optically driven pulse-width modulator to be used as part of auxiliary equipment during testing of electromagnetic compatibility of components intended to be built in vehicles. Due to the application in a test chamber, the modulator is designed as composed of two separate units connected by optical fibre. For the intended purpose, the inner unit had to be compliant with standards for automotive industry.
In order to see the inner unit's response when exposed to the same testing conditions as applied for tested samples, it had to be tested under the same conditions. For this purpose, the inner unit was loaded with 50 Ω load, which simulated the tested sample. The tests performed comprised: BCI (Bulk current injection), immunity to radiated electromagnetic fields and measurement of radiated emissions produced by inner unit while operating.
The results of the BCI and the immunity to radiated electromagnetic fields tests have shown that the inner unit is immune to disturbances produced in a frequency range from 1 MHz to 6 GHz, since during the tests there were no deviatons in the output signal of the inner unit. The measurement of radiated emissions produced by the inner unit while operating, however, showed that emissions were too high compared to the limit. Therefore additional measurements of emissions were done, which included changes in the circuit and test set up. Additional results have shown that high emissions are caused by differential conducted disturbances on input and output lines; furthermore, the results have also shown the correlation between the rise/fall times of the output signal and the produced emissions.
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