DECIMATION FILTER FOR ANALOGUE-DIGITAL CONVERSION AND INTERPOLATION FILTER FOR DIGITAL-ANALOGUE CONVERSION, CONCERNED WITH REDUCING COEFFICIENT WORD LENGTH IN FIR FILTER

摘要

PURPOSE: A decimation filter for analogue-digital conversion and an interpolation filter for digital-analogue conversion for reducing coefficient word length in an FIR filter are provided to reduce the size of hardware in case of using a multiplier by obtaining sufficient attenuation in an inhibition zone. CONSTITUTION: A decimation filter for analogue-digital conversion includes a plurality of FIR filters(4-1 to 4-3). The FIR filters are arranged by a cascade connection method. In the FIR filters, an insufficient attenuation region is generated from in an inhibition region of the last-stage FIR filter by shortening a coefficient word length of the last-stage FIR filter. The insufficient attenuation region is focused in the vicinity of a Nyquist frequency by determining a coefficient word of the last-stage FIR filter in order to attenuate the Nyquist frequency of the last-stage FIR filter.