Importance

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Abstract

In a stereo decoder, channel separation takes place with the aid of a demodulator to acquire signals for stereo operation. At low received field strength there is a continuous switchover to mono operation for each channel in the demodulator. For this purpose a switch is located in a signal path between input and output of the demodulator and driven by a PWM signal whose pulse-width repetition rate determines whether solely mono operation, solely stereo operation or a mixture of the two takes place. For generating the PWM signal, the field strength signal is compared with a triangular signal. To permit the switchover points between stereo and mono operation to be aligned by the manufacturer in accordance with the amplitude of the field strength signal, the apparatus contains two limit storage registers in which digital limit signals are set from outside. These limit signals are converted by a digital-to-analog converter into analog voltages which fix upper and lower limits the triangular signal, thereby determining the behavior of the triangular signal and thus also the pulse-width repetition rate of the PWM signal in accordance with the field strength signal.

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First Claim