TDA7406T datasheet(28/49 Pages) STMICROELECTRONICS

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TDA7406T

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The stereodecoder-part of the TDA7406T (see Fig. 25) contains all functions necessary to demodulate the

MPX-signal like pilot tone-dependent MONO/STEREO-switching as well as “stereoblend” and “highcut”. Adap-

tations like programmable input gain, roll-off compensation, selectable de-emphasis time constant and a pro-

grammable field strength input allow to use different IF-devices.

4.1 Stereodecoder-Mute

The TDA7406T has a fast and easy to control RDS-Mute function which is a combination of the audioproces-

sor'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 soft muted. Hence a checking of alternate frequencies could be

performed. Additionally the PLL can be set to “Hold”-mode, which disables the PLL input during the mute time.

To release the system from the mute condition simply the unmute-command must be sent: the stereodecoder

is unmuted immediately and the audioprocessor is softly unmuted. Fig. 26 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.

If any other source than the stereodecoder is selected the decoder remains muted and the MPX-pin is connect-

ed to Vref to avoid any discharge of the coupling capacitor through leakage currents. No further mute command

should be applied.

Figure 22. Signals during stereodecoder's SoftMute

Figure 23. Signal-Control via SoftMute-Pin

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