VALIDITY DECISION CIRCUIT CAPABLE OF CORRECTLY DECIDING VALIDITY OF AN ERROR SIGNAL IN A MULTILEVEL QUADRATURE AMPLITUDE DEMODULATOR

摘要

In a demodulator for demodulating a multilevel quadrature amplitude modulated signal specified by a plurality of output signal points arranged on an approximately octangular specific region into an in- phase baseband signal and a quadrature baseband signal and for converting the in-phase and the quadrature baseband signals into a demodulator output signal and an error signal, a validity decision circuit (40) is supplied with the in-phase and the quadrature baseband signals to decide that the error signal is valid when at least one reception signal point is outwardly of the approximately octangular specific region.