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TDA7407D

6.5

FUNCTIONAL DESCRIPTION OF STEREODECODER

The stereodecoder part of the TDA7407D (see Fig. 19) contains all functions necessary to demodulate

the MPX signal like pilot tone dependent MONO/STEREO switching as well as "stereoblend" and "highcut"

functions.

6.5.1 Stereodecoder Mute

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

cessor's softmute and the high-ohmic mute of the stereodecoder. If the stereodecoder is selected and a

softmute command is sent (or activated through the SM pin) the stereodecoder 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 con-

dition simply the unmute command must be sent: the stereodecoder is unmuted immediately and the au-

dioprocessor is softly unmuted. Fig. 20 shows the output signal VO as well as the internal stereodecoder

mute signal. This influence of Softmute on the stereodecoder mute can be switched off by setting bit 3 of

the Softmute byte to "0". A stereodecoder mute command (bit 0, stereodecoder byte set to "1") will set the

stereodecoder in any case independently to the high-ohmic mute state.

Figure 19. Block Diagram of the Stereodecoder

Figure 20. Signals During Stereodecoder's Softmute

SOFTMUTE

COMMAND

STD MUTE

t

D97AU638

t

t

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