In this report we will consider a special class of digital filter structure; and by structure we mean the particular arrangement and sequence of arithmetic and storage operations to realize a desired signal processing function. The more conventional structures consist of an interconnection of arithmetic operations such as addition and multiplication with storage elements such as memory registers. The filter is implemented in hardware by wireing together electronic modules that perform these functions or in software by a program that directs a general purpose computer to carry out the operations. These structures area analogous to analog or continuous time active and passive filters; indeed, many digital structures have exact analog counterparts as active filters.