Nonlinear feedback shift registers (NFSRs) are important building blocks for stream ciphers. The cascade connection of an n-stage full-length linear feedback shift register (LFSR) into an m-stage NFSR is called a Grain-like structure. In this paper, we focus on Grain-like structures which can generate minimal and maximal possible period sequences. The existence of Grain-like structures which can generate minimal possible period sequences is proved for the cases \(m=n\) and \(m>n\). The number of such Grain-like structures is estimated in both cases. Two necessary conditions are presented for Grain-like structures to generate maximal possible period sequences. Moreover, some interesting properties of such Grain-like structures are discussed.

非线性反馈移位寄存器（NFSR）是流密码的重要组成部分。将n级全长线性反馈移位寄存器（LFSR）级联为m级NFSR称为粒状结构。在本文中，我们集中于可以生成最小和最大可能周期序列的类晶粒结构。对于\（m = n \）和\（m> n \）情况，证明了可以生成最小可能周期序列的类晶粒结构的存在。在这两种情况下，都估计出这种类晶粒结构的数量。提出了两个必要条件，以使类晶粒结构产生最大可能的周期序列。此外，讨论了这种晶粒状结构的一些有趣的性质。