The Problem of CAN Bus Resonance When Performing CISPR25 Conducted Emissions Testing and Proposed Solutions to the Problem

When measuring a Device Under Test (DUT) using the Conducted Emissions Current Probe method (CE-CP) in the CISPR25 standard, the input impedance of the power lines must be controlled by Artificial Networks (ANs), whereas, the impedance of the Controller Area Network (CAN) communication lines is not controlled. As a result, unintended resonances take place on the CAN transmission lines, and the frequencies of the resonances change when the test set-up is changed. These unintended resonances lead to inconsistency in the measured data. In order to prevent this unintended resonance, the principle of resonance is studied using theoretical and experimental approaches. The resonant frequency changes as wire length changes such that the wire length is equal to
¹
/
₂
the wavelength of the resonant frequency. The resonant frequencies are also affected by the capacitance between the case of optical CAN converter and the ground plane. We have determined that the CAN transmission lines work as a gap-coupled half wave length resonator. After establishing the principle of the resonance, we have studied methods to control and suppress the unintended resonant noise generated from the optical CAN converter and have proposed strategies to improve the optical CAN converter set-up in order to achieve a reliable and accurate test results.