智慧型手機中耳機音頻輸入與輸出電路之電磁耐受度研究

Abstract

本篇論文以智慧型手機的耳機音頻輸出電路為實驗平台，研究在EN301489法規的輻射免疫性(RS)與傳導耐受性(CS)測試下，分析除錯前使用0201尺寸的BLM15HD182SN1 bead時所量測的上傳訊號(Uplink signal)與下載訊號(Downlink signal)，分別在8MHz~108MHz頻帶測試失敗的原因。針對RS與CS測試原理，分別找出電路上干擾傳遞路徑並且選出適當的bead來同時防止RS與CS測試的干擾訊號。同時bead不能影響聲音訊號與FM的RSSI值，又能防止地雜訊經FM的GND輻射到空中。根據實作結果，採用bead規格為BLM15EG121SN1與BLM15PD600SN1與BLM15PD800SN1皆可通過測試，選用的Rated current 要介於1500mA ~ 1700mA之間，Impedance@100MHz要挑選在60~120ohm之間，DC Resistance值介於2.2~0.06 ohm。

This ground line of the earphone audio circuit also doubles as the FM antenna of a smart phone. Its use, between, was found to caucal the phone to fail the radiaed and conducted susceptibility (RS/CS) tests per EN301489 standard in the frequency range 8MHz~108MHz. It was found that the ferrite bead used to connect the earphone to PCB ground should be replaced by an ofen bead with more appropriate DC resistance and RF impedance profile. A series of experiments were conducted to pick beads tha enable the phone to pass the RS and CS tests, while not compromise its FM neception, audio, and radiated emission (RE) performance.