Abstract: In digital transmission system, roll-off filter is usually used to shape the transmission wave form that does not produce Inter Symbol Interference (ISI). The roll-off filter must satisfy the Nyquests first criterion. But in many papers and books, only graphs are used to illustrate the construction of the characters of the shaping filters which were deduced from the Nyquests first criterion. The Nyquests first criterion was deduced according to Nyquests sampling theorem and used it reversely, and then the method to construct shaping filters which satisfied Nyquest's first criterion was given. The mathematical model is clear, and the result is same as the graph method.

Key words: Shaping filter , Nyquest’s first criterion , Sampling theorem , ISI

摘要： 数字传输系统中,通常应用滚降滤波器来形成无码间干扰的传输波形。滚降滤波器特性必须满足奈
奎斯特第一准则。然而文献和教材对该准则导出的形成滤波器特性的构成方法仅用图示的方法来说明。研究结果
表明,奈奎斯特抽样定理的逆运用可以导出奈奎斯特第一准则,且能给出满足奈奎斯特第一准则形成滤波器特性的
构成方法。其数学模型清晰,结果与文献和教材提出的方法得到的结果完全一致。

关键词: 形成滤波器 , 奈奎斯特第一准则 , 抽样定理 , 码间干扰