pi /4 SHIFT DQPSK MODULATOR

摘要

A pi /4 shift DQPSK modulator is provided with a mapping/filter circuit (6) that includes shift registers (61, 62, 63) for receiving phase data obtained for each symbol. Whenever the position data of one symbol is inputted, filter coefficient data, which have already been subjected to filtering processing, for 256 samples stored in advance are sequentially read out from a coefficient memory circuit (7), and these filter coefficient data are converted to numerical values by a numerical value conversion portion (65) on the basis of position data for 10 symbols which are outputted in parallel from the shift registers (61, 62, 63). In this way, filtered mapping data MF can be obtained. Accordingly, this invention provides a pi /4 shift DQPSK modulator which can reduce the number of gates of the filters and can accomplish drastic reduction of a circuit construction.