正交分頻多工(OFDM)之所以成為一熱門數位寬頻無線通訊技術，主要是由於其容易對抗高度分散傳輸的特性，而實現正交分頻多工接收機可行的方法是需要倚靠全方位的數位科技技術。 在這篇論文，我們討論的是關於高效能的低通濾波器設計之議題，此濾波器特別針對正交分頻多工接收機中的數位降頻器而設計，而接收機的輸入端為數位中頻訊號。數位降頻器中的低通濾波器所肩任的功能是同時抑制因降取(decimation)所產生的交迭頻帶內(aliasing bands)之鏡像訊號與雜訊，而鏡像訊號是因移頻(frequency mixing)所產生。由此新提出的基準所設計的低通濾波器與傳統規格的濾波器相比較，可得到效能上的增益趨勢。 Orthogonal frequency-division multiplexing (OFDM) is a favored technique in digital broad-band wireless communications due to its easiness to combat highly dispersive transmission. The feasible implementation of an OFDM receiver relies on fully digital technique. In this thesis, we discuss the issue regarding to the design of an efficient lowpass filter specifically for the digital down converter (DDC) in OFDM receivers with digital intermediate frequency (IF) input. The lowpass filter in the DDC possesses the function to suppress both the image band signal due to frequency mixing and the noise residing in aliasing bands resulted from decimation. The lowpass filter designed with a newly proposed criterion exhibits performance improvement comparing to those designed with traditional specification.
