使用展頻調變降低電磁干擾之無濾波器D類音頻放大器

Abstract

現今電子產品的發展逐漸朝向輕薄短小可攜式且能夠延長電池使用時間之高效率設計方式，如：助聽器、USB喇叭、筆記型電腦、無線喇叭及汽車音響放大器。而高輸出功率的設計可減少電源供應及散熱片的使用，進而縮小產品的面積。由於D類放大器擁有高效能之特性，因此逐漸的備受重視。 傳統脈波寬度調變技術運用在D類放大器時，在輸出級必須要有一組濾波器，這會造成整體面積和成本上的增加。因此，我們利用展頻調變技術去實現無濾波器之D類放大器，並藉此降低輸出端之EMI。還利用了負回授的機制來降低諧波失真，以提高其整體的線性度。此外亦利用非重疊的控制訊號去驅動功率電晶體，避免因為功率電晶體同時導通而產生貫穿電流，造成功率消耗及電路損毀。 放大器電路的設計是由TSMC 0.35μm 2P4M CMOS製程進行模擬，其操作電壓為3.3V。整個內部電路的細節在本論文中都會有詳細的敘述與討論。當我們給予一個振幅為0.8V且頻率在1KHz之正弦波為輸入信號時，我們可以得到總諧波失真為0.09%以及功率效能為86%。

Current portable electronic product requires small in size and high power efficiency for the long-term usage of batteries. The application products include hearing aids, USB speakers, notebooks, wireless speakers, and automotive audio amplifiers. The high power efficiency design can reduce power supply requirements and elimination of heat sinks, and also reduce the size of products. The Class-D amplifier, for its high efficiency, has drawn much attentions recently. A Class-D amplifier with conventional PWM modulation requires an output filter which needs large area and increasing cost. Therefore, we use spread-spectrum modulation scheme to realize a filterless Class-D power amplifier, and reduce output EMI. The negative feedback is applied in this thesis to reduce the harmonic distortion for better linearity. In addition, to avoid the shoot-through current when both power transistors are switched on at the same time, the dead time control is adopted. The circuit is designed using TSMC 0.35μm 2P4M 3.3V CMOS process. The details of the entire circuit will be described thoroughly in this thesis. When a 0.8V, 1KHz input sine wave is applied, the THD is 0.09% and the efficiency is 86%.