Patent ID: 7133527

Claim:
An arrangement for decoding a stereo multiplex signal, comprising: a baseband sum signal (L+R), a difference signal (L−R) which is amplitude-modulated on a suppressed sub-carrier and a pilot signal having a frequency located between the frequency bands of the sum and difference signals, a dematrix circuit an input for the stereo multiplex signal coupled through parallel stereo sum and difference signal paths to first and second inputs of the dematrix circuit, a synchronous demodulator being included in the difference signal path, a local sinusoidal sub-carrier being supplied to a carrier input of the synchronous demodulator for a synchronous demodulation of the amplitude-modulated difference signal (L−R) into baseband, an automatic gain control loop comprising a first mixer stage that is configured to receive a reference signal, a second mixer stage that is configured to receive a signal output of the first mixer stage, the first and second mixer stages having carrier inputs being supplied with the local sinusoidal sub-carrier for a respective up and down conversion of the reference signal, a difference circuit, operably coupled to the second mixer stage via an attenuator, that is configured to provide a difference between an output signal of the attenuator and the reference signal, a gain controlled amplifier stage, the difference circuit being coupled to a control input of the first gain controlled amplifier stage for varying a gain of the synchronous demodulator and the first and second mixer stages.