High-speed Wire Harness Crosstalk Analysis and Design Essentials for AR Glasses

In the extremely compact device of AR glasses, cameras, display modules, sensors, and high-speed main control boards are all crammed into a space the size of a fingernail, with resolution and bandwidth increasing all the time. The more high-speed lines and the higher the frequency, the more obvious the crosstalk problem becomes. I once encountered screen flickering and flashing issues while debugging an AR prototype, and it was finally confirmed that the problem was caused by near-end crosstalk (NEXT) between high-speed cables. The following is a summary of common crosstalk problems in AR devices and their solutions based on practical experience.

Why is crosstalk more likely to occur in AR glasses?

The internal space of the AR module is extremely small, and high-speed cables are almost all laid close to each other, resulting in a small spacing between cables and enhanced coupling of capacitance and inductance; after the signal reaches GHz, with fast edges and high energy, it is more likely to couple to adjacent lines. When the shielding layer, ground wire, or connector has discontinuities, crosstalk will be further exacerbated. I have seen projects where, during parallel testing with three micro coaxial cables, the far-end crosstalk (FEXT) increased by more than 5 dB, and the signal quality visibly declined, which is sufficient to demonstrate that crosstalk is difficult to avoid under high-density layouts.

Advantages and Hidden Issues of Micro Coax

AR products generally use micro coaxial cable, as it has stable impedance, good shielding, and high flexibility, which is very suitable for high-speed transmission in micro spaces. However, when several lines are bundled together, the shielding layers still couple with each other; shielding or grounding discontinuities at interface welding points, vias, and other places are more likely to become entry points for crosstalk. If the ground return is not smooth, common-mode noise will be more severe. In engineering, "small ground bridges (paddle card)" are commonly used to supplement the return path at the interface, which can significantly reduce common-mode interference and crosstalk.

III. Common Interference Phenomena in AR Scenarios and Engineering Countermeasures

Common crosstalk includes Near-End Crosstalk (NEXT), Far-End Crosstalk (FEXT), and common-mode coupling caused by discontinuities in ground return, which can lead to image jitter, false triggering, and screen glitches. To reduce crosstalk, it is usually necessary to start from the following aspects:

Proper cable bundle distance and arrangement; insert ground wire or empty wire when necessary; in multi-layer boards, make the wiring direction of adjacent layers perpendicular to each other.
Ensure complete ground reference and continuous return path, reinforce ground return in interface, transition area through-hole or shielding bridge.
Optimize the connector and interface design, adopting a structure with a metal shell or grounded finger piece to maintain continuous shielding.
Use differential signals (such as MIPI, LVDS) as much as possible to improve anti-interference capability.
When necessary, absorption materials, common-mode chokes, or adjusting pre-emphasis and equalization at the drive end can be added.
Identify problems in advance through SI simulation and actual measurements.

The essence of why glasses are prone to crosstalk is that high-speed signal density is high and the space is extremely small. Any point of return current or discontinuity in shielding will amplify interference. Micro coax is an excellent high-speed interconnect solution, but details such as interfaces, return paths, and shielding structures are often the key to signal quality. There is no single "magic component" that can solve crosstalk; it is more about overall optimization through the accumulation of many details.

I am[Suzhou Hui Cheng Yuan Electronic Technology]Long-term focus on the design and customization of high-speed signal cable harnesses and ultra-fine coaxial cable harnesses, committed to providing stable and reliable high-speed interconnection solutions. If you have related needs or want to learn more, please contact Manager Zhang.18913228573 (WeChat number)。