A Practical Technique Using Planar Coils to Make the Radiated Immunity of Specific Integrated Circuit Pins Less Dependent From PCB Orientation

Abstract

In this article, an inexpensive passive approach is proposed, both making the immunity of integrated circuits (ICs) less dependent on their orientation and controlling the immunity of specific pins. This technique is based on the introduction of planar 2-D coils surrounding the microcontroller ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\mu }$</tex-math></inline-formula> C) at the printed circuit board (PCB) level. The importance of the coil physical parameters (geometry, resonant frequency, and orientation) as well as the interference frequency is investigated, evaluating the difference in the magnetic field at the pin of interest in two opposite orientations (i.e., 0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> and 180 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> ). The effectiveness of the proposed technique is demonstrated in full-wave simulations and measurements, showcasing the provided immunity improvement through monitoring the behavior of the sensitive pins. Besides, this article strongly recommends IC designers not to place power supply pins close to the corners of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\mu }$</tex-math></inline-formula> C package due to the presence of the highest local tangential magnetic field when no structures are implemented. Coil orientation is shown to be the key adjustment parameter to enhance the immunity of any specific pin. The resonant frequency of the coils is found to be less relevant than its geometry and distance with respect to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\mu }$</tex-math></inline-formula> C pins. The proposed technique using the octagonal coils was also found to be effective in a wide frequency range (from 210 to at least 500 MHz). Compared to a no-coil case, an immunity enhancement of 74.2% (27.5%) is achieved in measurement (simulation) by the addition of an octagonal coil to the PCB, which clearly demonstrates the relevance of that simple approach for practical use in highly sensitive integrated electronics.