STEREO NOISE REDUCTION DEVICE IN FM STEREO RECEIVER

摘要

PURPOSE:To eliminate the feeling of disorder caused by changeover from the stereo reception into the monaural reception by forming internally a pseudo stereo state and changing the state over the said state when an S meter voltage is detected and the blend/high-cut state remains longer. CONSTITUTION:A pseudo stereo circuit is provided in parallel with a stereo demodulation circuit. A signal meter (S meter) output voltage (an S meter output voltage passing through a control circuit consisting of an amplifier 2, a negative rectifier and an adder 4) to control high-cut/blend is compared with a reference voltage Vref equal to the voltage starting the high-cut operation by a comparator 6, its output triggers a timer circuit 8 to generate a pulse and a discrimination circuit 9 consisting of an AND circuit discriminates whether or not a comparator output is in high level period, the result of discrimination is counted by a counter 10, the count preset in a preset counter 11 is compared with said result by a digital comparator 12, and when they are coincident, and the changeover switch SW for the pseudo stereo and the conventional multiplex system is changed over into the pseudo stereo operation.