STEREOPHONIC AND DOUBLE VOICE SIGNAL RECOGNITION SYSTEM

摘要

PURPOSE: To simplify the circuit constitution and to reduce the chip area for a PLL synchronous oscillator exclusive for the specific signal frequency that is used for the FM modulation by making use of a small ratio between the highest and lowest frequency levels of the oscillator and performing the reproduction in a full range of frequency by means of only one oscillator. ;CONSTITUTION: A circuit which recognizes the stereophonic and double voices consists of a second intermediate frequency amplifier 200 which amplifies a 2nd voice signal, a BPF 210 which filters the output signal of the amplifier 200, an AM detector 220 which detects the value of the output signal of the filter 210, a control voltage oscillator 230 which generates the frequency of both stereophonic and double voices, an LPF 250, a counter 260 which counts the signal amplitude number within a fixed time and produces an output signal according to the counted amplitude number, and a selector 270 which selects the stereophonic and double modes based on the output of the counter 260. In such a constitution, the number of necessary elements is reduced and the operating reliability is improved for the circuit.;COPYRIGHT: (C)1994,JPO