低功率低失真無濾波級之BD類功率放大器

Abstract

放大器對一個音響系統扮演著很重要的角色。在目前音響系統中市場仍以AB類放大器為主要設計。若以功率效益方面來比較，D類功率放大器有較優越的輸出功率表現。主要是因為D類功率放大器是以切換的方式來完全導通或是完全關閉電晶體。因此D類功率放大器可以擁有AB類放大器較少的功率消耗。

本論文重心著重於發展一種高功率效益D類功率放大器的調變方式。此電路有別於傳統全橋式D類功率放大器，它改善了傳統D類功率放大器訊號失真過大的缺點，同時卻不因此使得功率效益變小；改善方法是藉由加入回授系統；這是一種降低雜訊的技巧；並且改變脈波寬度調變的方式來實現電路(BD類)。此外，所設計的電路還有一項優點，就是不需要D類功率放大器的輸出濾波級，此技術使得電路的面積變小，功率效益提高。

BD類調變技術的開發，大大減少或消失輸出濾波器。無輸出級濾波器的調變方案最大限度地降低開關電流，使揚聲器被用作代替LC濾波器，並且放大器還能有效的動作,並且非對稱BD類放大器架構能有效改善失真特性。

Audio amplifiers play an important role in the audio system. Class-AB amplifiers in terms of linearity are superior in recent markets. Compared by power efficiency, Class-D power amplifiers have better performance than Class-AB amplifiers. It is based on the fact that Class-D power amplifiers use the switching operation to fully turn on or off the Power Mosfet. Class-D power amplifiers have less power dissipation than Class-AB amplifiers. The focus on this thesis is to develop technique of modulation of Class-D amplifiers with high and reduce EMI power efficiency. This circuit is different from the traditional H-bridge Class-D power amplifier. It has improved the shortcoming of the traditional Class-D power amplifier without degrading signal linearity, and also keep the power efficiency. And the circuit is realized by changing the way of the Pulse Width Modulation（PWM） method (Class BD). In addition, this circuit has another advantage that it eliminates the Class-D output filter. This technology can reduce the area of the circuit and can improve power efficiency at the same time. Class BD modulation scheme developed to greatly reduce or eliminate the output filter. The filter-free modulation scheme minimizes switching current, which allows a speaker to be used as the storage element in place of an LC filter and still lets the amplifier be very efficient. And novel asymmetric class BD amplifier architecture can effectively improve the distortion characteristics.