Stereo/two-tone demodulator

Abstract

In a stereo/two-tone demodulator for demodulating an intermnediate-frequency signal having stereo or two-tone sound signals modulated on a first and a second sound carrier, the second sound carrier having a lower amplitude than the first sound carrier, ceramic filters or bandpass filters are saved and complete integration can be achieved in that a first (1) and a second (2) linear narrow-band phase-locked loop are provided each having their own frequency selectivity, the first narrow-band phase-locked loop (1) being implemented in such a way that it locks in at the frequency of the first sound carrier, and the second narrow-band phase-locked loop (2) being implemented in such a way that it locks in at the frequency of the second sound carrier. The first narrow-band phase-locked loop (1) is preceded by a first amplifier stage (4) and the second narrow-band phase-locked loop (2) is preceded by a second amplifier stage (5), each amplifier stage controlling the input signal of the subsequent phase-locked loop (1; 2) at a nominal amplitude. A carrier suppression circuit (3) is provided in which an output signal having a phase position of 0° or 180° of a voltage-controlled oscillator (20) of the first narrow-band phase-locked loop (1) and the input signal of the first narrow-band phase-locked loop (1) are superimposed and which supplies a modified interrnediate-frequency signal as an output signal in which the first sound carrier is suppressed and which is coupled to the second amplifier stage (5) preceding the second narrow-band phase-locked loop (2).

Dependencies are inferred from the claim text.