光碟機內的資料讀取通道由於頻寬有限，造成讀出訊號(RF)會有高頻衰竭的現象。此外，碟片上因壓製過程的缺陷，或讀取過程之外來雜訊干擾等，均會導致RF訊號中存在非線性失真。
此外，根據數位通訊理論中之奈奎氏準則(Nyquist criterion)，當訊號之取樣頻率的一半(亦即為奈奎氏頻率，Nyquist frequency)超過讀取通道頻寬時，理論上沒有等化器(不管是線性或非線性)可以完全克服符際干擾的影響。這一個限制相當於限制了光碟機的資料傳輸速率。因此，為了提高讀取倍速，就得犧牲完全不能有符際干擾的嚴苛限制。為了避免引入不想要的符際干擾，造成訊號檢測還原的困擾，在訊號處理過程中就必須允許可受控制的符際干擾，也就是所謂部份響應(Partial Response，PR)技術的精神。一旦訊號的符際干擾為我們所控制，則吾人就能在最後訊號檢測的階段，利用最大期望值數列估測(Maximum Likelihood Sequential Estimation，MLSE)技術克服符際干擾及外加雜訊，將讀取訊號還原成記錄在碟片上之二元(binary)資料。此一等化、檢測的機制就被稱作PRML系統。

如何等化RF訊號以降低訊號時基偏移比(jitter ratio)，一直以來都是一個很重要的議題，尤其是在高頻訊號衰竭及符際干擾都較嚴重的DVD中。首先，本文藉由光碟機讀取通道之數學模型，模擬不同倍速之RF訊號，再根據此訊號設計各種等化器應用在PRML系統中，並分析其效能；接著，本文再由實際光碟機擷取真實RF訊號做進一步的驗證。實驗結果證明了在PRML系統中，利用以類神經網路為基礎之非線性等化器會較線性等化器有較優異之性能表現。

In DVD-ROM, how to equalize the read-out radio frequency (RF) signal to reduce the jitter ratio has been an important issue so far. In this paper, we investigate the characteristic of the optical channel model in DVD-ROM and propose an Adaptive Neuro-Fuzzy Inference System (ANFIS) based equalizer together with a viterbi detector to form as a partial response maximum likelihood (PRML) system for DVD-ROM. Jitter performance using ANFIS based equalizer is compared with that of other linear filter based equalizers. By computer simulation, it shows that the proposed equalization method has better jitter performance than conventional linear filter based equalizers for the optical channel in DVD-ROM.

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