DEVICE FOR SWITCHING DEMODULATOR CONTINUOUSLY FROM STEREO TO MONAURAL OR VICE VERSA

摘要

PROBLEM TO BE SOLVED: To switch stereo and monaural reproduction with a stereo decoder as an IC circuit that executes the adjustment of a reference triangle wave signal without using the external parts. SOLUTION: In a changeover device, a difference signal of multiplex stereo signals supplying the signals to input terminals of a demodulator with an RF part having a variable element so as to obtain separation signals of two cannel systems at two output terminals is added to an adding signal of the multiplex stereo signals, the variable element is composed of a switch placed on a signal path between the input terminals and each of the output terminals and driven by a PWM signal whose the pulse width repetitive rate varies in accordance with an electric field strength signal and the electric field strength signal is compared with a reference triangle wave signal whose the amplitude is varied between an upper limit value and a lower limit value. In this case, a stereo decoder is provided with at least one limit value storage registers 22, 24 to which an external digital signal is inputted from the outside of an audio processing unit so that after being converted into an analog voltage, the analog voltage is transmitted to a triangle wave generator 30 as a limit value.