Abstract

This publication describes printed circuit board layout techniques for reducing audio-band magnetic noise near a magnetically sensitive element or region of a compact electronic device, for example, in the hearing aid compatibility (HAC) region surrounding the audio receiver of a mobile device, such as a smartphone, or a similar sensitive region of a wearable audio device, such as a wireless earbud or a headphone. High-current power traces, such as a battery rail or a system supply rail, can be a significant source of the low-frequency magnetic noise that a hearing aid telecoil, a wireless earbud having hearing-assistance features, or an HAC test probe measures in this region. In a first technique, a slot is formed in a ground plane along a path that mirrors an adjacent power trace, leaving an isolated strip of the ground plane, referred to here as a return strip, that carries the return current directly alongside, and antiparallel to, the supply current. The closely spaced, opposing currents may generate magnetic fields that largely cancel, in particular the in-plane (horizontal) field component evaluated in HAC testing. In a second technique, the power trace is routed in a serpentine pattern so that adjacent trace segments carry current in opposite directions and their fields partially cancel, without modifying the ground plane. A combined implementation pairs serpentine routing with a partially isolated return strip that follows the serpentine, which in some instances provides further noise reduction while limiting the effect on the power delivery network. In example simulations, the peak horizontal magnetic field in the HAC test region was reduced by approximately 42 to 52 percent with serpentine routing alone and by approximately 89 percent with the combined implementation, relative to a straight trace over a solid ground plane.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Download

Share

COinS