微波技術 - 5G的高頻段如何影響信號完整性？

5G的工作頻率將遠高於4G, 迫使PCB設計師重新考慮 電路板 設計和製造方法.
隨著5G的出現, electrical engineers must reconsider (and sometimes redesign) their PCBs and other infrastructure to support the high frequencies of the new spectrum. 信號完整性將成為5G PCB板設計中的首要問題.

5G's position on the electromagnetic spectrum
In this article, 讓我們看看高頻對PCB信號完整性的影響以及緩解這些問題的方法.

為什麼5G頻率對信號完整性不利?
電路板設計中, 頻率的新增將對信號完整性產生許多不良影響，尤其是雜訊和衰减新增的影響.

Noise
Regarding noise, 首先要考慮的是，隨著系統頻率的新增, 訊號反射變得越來越重要. 根據傳輸線理論, 反射與傳輸線長度與訊號波長之比直接相關.

Signal reflection
We also know that the signal wavelength decreases as the frequency increases (λ = v / f). 因此, 因為5G引入了更高的頻率, 設計者還必須考慮訊號反射的影響, 例如鈴聲或其他失真, 這將在系統中產生更多雜訊，並有效降低SNR.

Capacitive and inductive coupling
In addition, 因為電容和電感與電壓和電流的變化率有關, 分別地, 電容耦合和電感耦合的影響變得更加相關. 這也會產生譟音和失真, 降低了信噪比.

Attenuation and skin effect
Regarding attenuation, 一個重要的考慮因素是所謂的趨膚效應. 它本質上表明，隨著訊號頻率的新增, 訊號在導體中的穿透深度减小.

Skin effect
The important meaning of the skin effect is that as higher frequencies pass through a smaller area, 它們將遇到更大的阻力，並導致更大的紅外損耗. 這種損耗也會降低SNR.

Ways to improve SNR in 5G design
In high-speed design, 影響信號完整性的因素有很多. 所以, 5G PCB板的設計者能做什麼?

Control circuit board impedance
An important step to reduce signal reflection and attenuation is to control the impedance of the circuit board. 具有正確端接的接線和設計良好的阻抗匹配網絡對於防止訊號反射和為電路模塊提供最大功率至關重要.
Focus on impedance in manufacturing: mSAP
The impedance control problem can also be solved when manufacturing circuit boards. 傳統的PCB制造技術存在創建梯形橫截面軌跡的缺點. 這些橫截面將改變軌跡本身的阻抗, 這嚴重限制了5G應用.
One solution is to use mSAP (semi-additive manufacturing process) technology, 這使得製造商能够以更高的精度創建跟踪. 控制電路的幾何形狀也有助於緩解集膚效應和由此引起的訊號功率損失.
減法和mSAP過程. Image courtesy of Proto-Electronics
Place components and traces
When mitigating effects such as coupling, 最重要的是明智地將組件和軌跡相互連接並接地. 例如, 具有埋置地平面和電源平面的多層PCB可能是一個有用的解決方案.
Placing sensitive lines near the ground plane forces capacitive coupling with ground (as opposed to other lines) and provides a low-inductance return path for high-speed signals.
More considerations for 5G design
Although this article does not address an exhaustive list of all issues or solutions, 我們回顧了5G頻率中信號完整性的一些高級問題以及解决這些問題的可能設計解決方案.
明顯地, 5G將給PCB工程師帶來信號完整性挑戰, 因為雜訊和衰减的頻率相關效應會降低SNR. 成功的5G設計, some factors not considered in this article (such as the choice of dielectric and substrate 材料) are equally important.