Common Mode Voltage Evaluation for choosing Quiet MCU and Optimizing PCB Design: Electromagnetic Emissions Measurement for Integrated Circuits

Similar to the fact that the differential signaling interfaces radiate less amount than the typical single ended interfaces, radiation from wire harness connected to electronic control units using single chip micro computers can be reduced by adjusting the common mode voltage fluctuation of supply lines. The radiation from wire harness can be minimized when the Vcc and the Vss fluctuate with same magnitude in opposite phase. As estimating these fluctuations of real products using lots of components on complex PCB layout by simulation technique is quite difficult at this moment, alternative solution to investigate the common mode voltage fluctuation has been investigated. By the Workbench Faraday cage method and advanced usage of it with 180 deg four ports hybrid balun, common mode voltage fluctuations of Vcc and Vss with phase information can be monitored. Examples of this measured data are discussed and a way of reducing common mode radiation from wire harness is explained.