EMI Reducing Inverted F Slot on Reference Plane of Mixed Signal Design

Abstract

In mixed-signal design, slots on reference planes are the most preferred choice to isolate return currents of sensitive analog and noisy digital signals. However, the discontinuity caused by these slots in the return current path leads to unwanted radiation, which causes electromagnetic interference (EMI) issues. Hence, in this context, we propose inverted F slot structure to be used in place of the conventional slot structure, which alleviates the return current path discontinuity and provides a low impedance path for return current. This, as a result, reduces unwanted radiation. The proposed inverted F structure is suitable for rigorous parametric analysis by its versatile geometry, allowing the user to tune the structure size to minimize the radiation at the desired frequency. Furthermore, the simulations of the inverted F slot structure, performed on a 70x45mm RO4003 Rogers PCB in the frequency range of 1-5GHz, show a maximum improvement of 55dB with inverted F slot and 32dB with inverted F split, which outperforms the existing solutions.