RFI Mitigation System for Smart Phones by Automatic Calibration of MIPI Data Rate

This paper presents a method for mitigating Radio Frequency Interference (RFI) in smart phones caused by noise radiation from Mobile Industry Processor Interface (MIPI) D-PHY. As the imaging performance of camera modules in smart phones improves continually, the data rates of image signals, which can be a factor of Electromagnetic Interference (EMI), are increasing, thereby raising the possibility of RFI generation in built-in antennas. Our RFI mitigation system utilizes Received Signal Strength Indicator (RSSI), a metric for the strength of received signals in wireless communication, as a feedback control variable. While a camera module captures images, an Application Processor (AP) dynamically calibrates MIPI data rates, monitoring fluctuations in RSSI, thus preventing interference from MIPI DPHY noise radiation within channels. The proposed method is realized through software operations on an AP, thus enabling its application to any IC module controlled by an AP. This method does not require additional new EMI countermeasure components, thereby reducing component costs and evaluation efforts in smart phone EMC design. The effectiveness of this method was measured using a test board equipped with an image sensor and a test circuit emulating a Radio Frequency (RF) circuit inside a smart phone. The method confirmed the mitigation in wireless interference to be sufficient, measuring approximately 9.1 dB.