A Filtering Method for Reducing Computations and The Gaussian Lowpass Filter and The Modulator Using the Filtering Method therein

摘要

PURPOSE: A filtering method for reducing calculation capacity, a Gaussian filter using the same, and a modulator having the Gaussian filter are provided to perform rapidly a filtering process regardless of increase of the number of samples per data bit. CONSTITUTION: The filter output signal components are calculated in each sample of normalized data related to an output of a filter. The calculated filter output signal components are stored in a ROM. A data storage circuit(30) is used for storing 3-bit ((2(L/2)+1)=3) data. A ROM table(32) is used for storing the varied amount of phase. The varied amount of phase corresponding to recent normalized data of 3-bits is stored in the ROM table(32). The varied amount of phase corresponding to inputted data is read from the ROM table(32) when three data are inputted from the data storage circuit(30). Sizes and signs of the varied amount of phase are controlled according to signs of data. The varied amount of total phase is calculated by adding sizes and signs of the varied amount of phase.