TDA7406T Datasheet, PDF (28/49 Pages) STMicroelectronics – CAR RADIO SIGNAL PROCESSOR

TDA7406T
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 V_O 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 V_ref 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
28/49