A fast & simple RFI mitigation method without compromising signal integrity
In modern wireless consumer electronic devices, there is an increasing need for smaller, compact, and denser design. This often requires wireless components like transceiver, front-end and antenna to be placed very close to noise sources like memory, power supply, and main processor in the device. Electromagnetic noise from noise sources interferes with wireless receiver components causing radio frequency interference (RFI) issues in the device. As a result, wireless performance metrics like range and throughput is degraded, which impacts the user experience. In this paper, a popular consumer electronic device is studied. The device has many complex subsystems like CPU, DDR memory, and power supply co-located with Wi-Fi circuitry. Due to small size, the device has RFI issues from CPU memory interface, which affects the Wi-Fi range. Typically, RFI problem can be mitigated from a mechanical design perspective by adding shield can, or from a signal integrity perspective by modifying clock and slew rate of the high-speed signals. In this paper, a novel RFI mitigation method is proposed. Through near-field scanning, an equivalent dipole moment of the noise source (CPU and DDR3) is reconstructed, and the near-field components of the victim (Wi-Fi antenna) are measured. By determining relationship between dipole moment and antenna near field, the noise source is rotated by a certain angle to reduce RFI. Rotating the source to reduce RFI is implemented in such a way that it doesn’t compromise signal integrity, and it doesn’t require an additional shield can. New boards with the suggested changes are fabricated and the measured results show a good RFI reduction (up to 8 dB) compared to original boards.