臺灣博碩士論文加值系統

類比至數位轉換器資料的轉換屬於非線性的處理過程，非線性系統可能產生一個比輸入訊號較大頻寬的輸出訊號。根據奈奎式取樣定理，
取樣頻率必須大於等於兩倍輸出訊號頻寬，否則輸出訊號會出現失真的現象。然而如果輸入訊號是一個帶通訊號，輸出訊號頻譜通常佔了多個頻帶。在這種情況下，如果使用帶通取樣的的觀念，可以使輸出訊號的取樣頻率降得比奈奎式取樣頻率低很多。在這篇論文中我們為非線性類比至數位轉換器取樣帶通訊號這個問題，找出適用的帶通取樣頻率，來迴避因非線性系統的諧波以及互調制失真頻譜所造成的影響，並有效的降低射頻訊號的取樣頻率。與文獻中現有方法不同的地方，本論文所提出之方法是以輸入主訊號為主要考量，並不是把輸出所有的非線性頻譜皆隔離開來，而是以帶通取樣後保留主訊號為目的。這樣的作法讓取樣頻率的選擇更有彈性，也能得到較低的適用取樣頻率。

The conversion of analog signals to digital signals using an analog-to-digital converter(ADC) can beviewed as a nonlinear process. Nonlinear systems may produce an output signal with a wider bandwidth than that of the input signal. According to the Nyquist sampling theorem, the sampling rate needs to be at least twice the maximum frequency of the output signal, otherwise the output signal will be distorted due to aliasing.However, if the input signal is a banpass signal, the spectrum of the output signal often occupies multiple bands. By using the bandpass sampling concept, one can sample the output signal at a rate much lower than the Nyquist sampling frequency. In this thesis, we deal with the problem of sampling bandpass signals using nonlinear ADCs. We find appropriate bandpass sampling frequenies for avoiding the distortions caused by the harmonic and intermodulation spectra, owing to the nonlinear systems. It turns out that we can significantly lower the sampling frequency for RF signals. Compared to other methods we found in the literature, the proposed method avoids overlapping of the main signal spectrum to nonlinear spectrum and alows the overlapping of the nonlinear spectra to one another. This makes the selection of the sampling frequency more flexible and results in a lower sampling rate.

1.緒論
2.類比至數位轉換器與帶通取樣
3.以非線性ADC帶通取樣射頻訊號
4.保留主訊號之非線性ADC帶通取樣方法
5.類比至數位轉換器上之實驗與模擬驗證
6.結論

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