金屬共振腔內數位類比轉換耦合之雜訊分析及抑制設計

Noise Analysis and Suppression Design for Digital-to-Analog Coupling in Shielding Cavity

詹皓崴(Hao-Wei Chan)

指導教授 ： 吳瑞北

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201804228

摘要

一般電路板在核心晶片上方加蓋金屬共振腔，以增加導熱與阻隔外界電磁干擾，但也會造成數位導線訊號耦合至類比導線，本論文旨在發展兩種設計原則，以抑制此一數位至類比訊號的耦合雜訊。與傳統使用高導鐵磁性材料的解決方案相比，本研究提出的方法具有低成本及高設計靈活性，並可在需求頻段進行高程度抑制。
第一個抑制方法是提出短路針腳結構，配合電路內數位訊號功率頻譜，改變空腔共振移至頻譜密度節點，使得雜訊源對射頻元件的影響最小，理論及實驗結果證實其可使頻域類比耦合雜訊降低30 dB，時域數位雜訊降低達三成。
第二個抑制方法是提出共振抑制器結構，直接干擾共振時空腔內表面電流分布使共振模態影響降低。共振抑制器是利用槽孔二分之波長共振原理，將其微小化後放入空腔內表面電流最強區域。此方法對耦合雜訊抑制能力可達10 dB，且微小化結構其電路尺寸只有十分之波長。

關鍵字

電磁干擾 ； 數位類比耦合 ； 功率頻譜密度 ； 雜訊抑制器 ； 雜訊吸收

並列摘要

The metallic shielding cavity is commonly used on top of the main CPU chip in the printed circuit board, to provide good heat dissipation and block electromagnetic interference (EMI) from outside environment but also incur significant coupling from the signal in digital traces to analog traces. This thesis is dedicated to the development of two different noise suppression method to mitigate the coupling noise through shielding cavity. As compared with the conventional solution using ferrite-based absorbing material, the proposed two methods not only feature cost-efficiency and design flexibility, but also provide high suppression level at desired frequency band.
The first mitigation method proposed a shorting pin structure. Given that the digital signal has nodal points at every integer value of clock rate, the shorting pin connecting the cavity and top ground plane is used to shift cavity resonant frequency to a near nodal point, thereby minimizing the effects of coupling noise on the RF circuits. Both the simulation and measurement validated its efficiency in reducing coupling noise at desired frequency by 30 dB and for transient digital signal by 30%.
The second mitigation method proposed a resonance suppressor structure. Cavity modes can be reduced if the surface current distribution of cavity is perturbed by the suppressor. By utilizing λ/2 slot resonators with miniaturization, the current will be trapped by the suppressor at its resonance, resulting weaker resonant mode. The proposed method can suppressed coupling by 10 dB with size only one-tenth of wavelength.

並列關鍵字

Electromagnetic interference (EMI) ； digital-to-analog coupling ； power spectral density ； noise suppressor ； noise absorption

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