FOUR PHASES DEMODULATION CIRCUIT AND PHASE COMPARATOR OF FOUR PHASES DEMODULATION CIRCUIT

摘要

PURPOSE: To obtain stable detection output even if the amplitude of QPSK signals is not constant by digital-processing the A/D-converted QPSK signals by means of ROM tables corresponding to reproduced carriers, multipliers, digital LPF and a phase difference detection circuit so as to demodulate them. ;CONSTITUTION: The digital QPSK signals passing an A/D converter 24 are multiplied in the multipliers 2 and 3 by Cosωct and Sinωct signals which are the outputs of VCO 30 passing a frequency-dividing circuit 31, are read from the ROM tables 25 and 26 and whose phases are precisely different by 90°. They are inputted to the phase difference detection circuit 34 through digital LPF 27 and 28 and a demodulation clock and demodulation data are outputted. Thus, stable detection output can be obtained even if variance does not exist in a circuit parameter and the amplitude of the QPSK signal is not constant by a digital processing using the ROM tables.;COPYRIGHT: (C)1995,JPO