TDA7407 datasheet(26/46 Pages) STMICROELECTRONICS

26 / 46 page

Multipath detector

TDA7407

26/46

5.2

Functional description of the stereo decoder

The stereo decoder part of the TDA7407 (see Figure 18) contains all functions necessary to

demodulate the MPX signal like pilot tone dependent MONO/STEREO switching as well as

"stereoblend" and "highcut" functions.

5.2.1

Stereo decoder Mute

The TDA7407 has a fast and easy to control RDS mute function which is a combination of

the audioprocessor's softmute and the high ohmic mute of the stereo decoder. If the stereo

decoder is selected and a softmute command is sent (or activated through the SM pin), the

stereo decoder will be set automatically to the high ohmic mute condition after the audio

signal has been softmuted.

Hence a checking of alternate frequencies could be performed. To release the system from

the mute condition, the unmute command must be sent: the stereo decoder is unmuted

immediately and the audioprocessor is softly unmuted. Figure 19 shows the output signal

VO as well as the internal stereo decoder mute signal. This influence of Softmute on the

stereo decoder mute can be switched off by setting bit 3 of the Softmute byte to "0". A stereo

decoder mute command (bit 0, stereo decoder byte set to "1") will set the stereo decoder in

any case independently to the high ohmic mute state.

Figure 18.

Block diagram of the stereo decoder

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