球柵陣列封裝布局與打線訊號干擾效應最佳化研究

Abstract

本篇論文以智慧電視(Smart TV)為實驗平台，研究主畫面正常播放影片時語音類比轉數位(Audio ADC)的輸入被背景收台並在同一個畫面輸出( Picture-in- Picture，PIP )之類比電視信號(ATV)Audio DAC接地電流回流透過共同之下地貫孔造成干擾的問題。將Audio DAC的非同步頻差電流藉由增加接地貫孔降低等效阻抗可降低感應電壓變化。此外，透過分離Audio ADC接地路徑，避開共用路徑與降低互感，也可使DAC差頻電流產生的影響降到最低，才不會被Audio DAC取樣雜訊干擾，這些做法可以有效減少Audio DAC電流噪音而降低開關雜訊干擾。 本論文利用ANSOFT HFSS商業軟體模擬分析，模擬改善接地貫孔路徑以降低球柵陣列結構印刷電路板(Ball Grid Array ,BGA)之間相互的干擾。實驗結果顯示，改善電流回流貫孔路徑的做法在Audio ADC模組內的干擾問題上面，可獲得16-dB的改善效果。

This thesis uses smart TV as the experimental platform to study the interference originating from audio DAC (digital-to-analog converter) ground return currents to audio ADC (analog-to-digital converter) ground through the same return path when the TV operates in the PIP (Picture-in-Picture) mode in witch both the main screen and the background analog TV play video and voice. Increasing the number of vias used for the audio DAC’s non-synchronous frequency-differential currents and go to the ground directly, will reduce the path’s impedance and the induced voltage changes. In addition, separating Audio ADC’s ground path to avoid the common current path and reducing mutual inductance can also minimize the impact of the DAC difference-frequency currents and avoiding interference from Audio DAC sampling noise. These practices can effectively reduce audible noise due to audio DAC noise and switching noise. In this thesis, we also use ANSOFT HFSS to do simulation. Simulation results indicate that improving the ground and power path return current reduces mutual interference. After improving the current return path in the BGA package, experiment as measurements show that the interference level found in the audio ADC module is significantly reduced by 16 dB.