改良失真度之直接數位化頻率合成器

Abstract

在許多電子工程上的應用,常常需要使用純度極高的正弦波來當作其信號 源.其中最為有名的,就是用look-up table DDFS來產生這個純度極高的正 弦波.但是,傳統上的DDFS,其經由D/A Converter仍然輸出一種以階梯的形 式來產生這個正弦波.如果我們用斜波的方式代替階梯的方式來產生這個 正弦波,那麼這個正弦波一定會變的比較平滑.也就是說,此正弦波的諧波 會降低很多.本論文提出一種新的方法來產生這種斜波式的正弦波. In many applications of electronic engineering, an extreme pure sine wave is always needed as a signal source. And the look-up table Direct Digital Frequency Synthesizer(DDFS) is the most famous structure for generating this extreme pure sine wave. But in conventional DDFS, via D/A Converter, the output signal is reconstructed to a continous sine wave in stepping way. If we use a slopping way instead of stepping way to reconstruct the sine wave, this sine wave must be more smooth. That is to say, the harmonics of the reconstructed sine wave would be reduced a lot. In this thesis, a new method that based on the conventional DDFS which would be arisen to produce a sine wave in slopping way.