JPS647733A - Multiplex demodulating circuit - Google Patents

Abstract

PURPOSE:To digitally demodulate a composite signal with a simple constitution by separating a pilot signal from a digitally composite signal, delaying one side of both signals to other side, mutually making it into a negative phase, adding it and cancelling a pilot signal component. CONSTITUTION:A composite signal including a pilot signal is inputted to a filter 1, the noise component of the 1/12, 3/12, 5/12 and 6/12 of a sampling frequency fs is removed by adder circuits 11-13 and delaying circuits 14-16, controlled to a signal at a prescribed level with a multiplying circuit 2 and the pilot signal is separated by a BPF 3. The phase of the pilot signal is changed by 180 deg., an adder circuit 6 adds it with a composite signal delayed from a delay circuit 4 and the pilot signal is cancelled. On the other hand, the output of a BPF is inputted to a generating circuit 7 and a rectangular wave and an approximate sine wave are outputted from exclusive OR circuits 75 and 77. These signals are multiplied with the output of the circuit 6 by a multiplying circuit 8, a sub-voice signal is outputted, synthesized with a main voice signal by a matrix circuit 10 and a composite signal is demodulated.