推挽式放大器之動態偏流控制電路的設計與實現

Abstract

放大器可以被區分成好幾類，如A類、AB類及B類或G類…等等。其中有些類別在理論上只是彼此的靜態工作電流（偏流）上有些差別，其餘的部份則大同小異。換言之，只要某一部放大器的設計夠完善，透過調整它的偏流，我們便能夠將它從原先的類別改變成另外一類。另一方面，當放大器在使用時、很可能因為內部零件受到溫度上升的影響、抑或是來自於外界的干擾使得它的偏流大幅度地便動。這會令原本是高傳真的A類放大器降級成大偏流的AB類放大器而喪失了原有的好特性。甚至更糟糕的是，它們可能會因為放大器機箱內的溫度太高而使得偏流大幅提升至超過原先設計所能容忍的範圍，以致於毀損放大器。 在本文中、我們提出一組能有效地以動態方式控制推挽式放大器的偏流的電路。更進一步地說，我們引用了負迴授技術讓偏流獲致穩定並使它能夠跟隨輸入訊號動態地變化，以減低功率消耗。在此我同時列出這組電路在推挽式放大器上的多種應用。最後我也花時間進行電路實驗來證明它的可行性與表現。 文中當然也包含了使用套裝軟體作設計模擬。

Amplifiers are divided into several classes, class-A, AB and B or G…etc [1]. Some of them differ only in their bias-current theoretically. In other words, by adjusting the bias-current of an amplifier, we can get one different class out of another as long as the original amplifier is properly designed. Besides that, when they are working, chances are their bias-current varies a lot due to a wide temperature change in their elements and/or some disturbance from outside. Then, an amplifier certified as high performance Class-A could possibly degrade to high bias-current class-AB. Or, even worse, it can be destroyed if its bias-current exceeds too much the preset value, because of the extremely high temperature inside the chassis that encloses this amplifier. In this thesis I propose a set of effective circuits to control bias-current dynamically at the output stage of a push-pull amplifier. That is, in an attempt to stabilize the bias-current while allows it to vary with input signal dynamically in order to reduce power dissipation, I borrow the idea of negative feedback technique and find out a way to realize it. At the same time I also show the varieties of its application on push-pull amplifiers. Finally, I spent lots of time to experiment some of those applications in more practical way and check their performance. Of course, simulations using MATLAB and SPICE are also presented. I hope this thesis can offer some good experiences to people who are interested in amplifier design and of the most wishes, give me any advice you have in your mind.