TDA7406 Datasheet, PDF (36/64 Pages) STMicroelectronics – Car radio signal processor

Functional Description of Stereodecoder
Figure 24. Signals during stereodecoder's SoftMute
TDA7406
Figure 25. Signal-Control via SoftMute-Pin
8.2
InGain + InFilter
The InGain stage allows to adjust the MPX-signal to an internal magnitude of about 1V_rms
which is the recommended value. The 4.th order input filter has a corner frequency of 80kHz
and is used to attenuate spikes and noise and acts as an anti-aliasing filter for the following
switch capacitor filters.
8.3
Demodulator
In the demodulator block the left and the right channel are separated from the MPX-signal.
In this stage also the 19-kHz pilot tone is cancelled. For reaching a high channel separation
the TDA7406 offers an I²C-bus programmable roll-off adjustment which is able to
compensate the lowpass behavior of the tuner section. If the tuner's attenuation at 38kHz is
in a range from 7.2% to 31.0% the TDA7406 needs no external network in front of the MPX-
pin. Within this range an adjustment to obtain at least 40dB channel separation is possible.
The bits for this adjustment are located together with the fieldstrength adjustment in one
byte. This gives the possibility to perform an optimization step during the production of the
car radio where the channel separation and the fieldstrength control are trimmed. The setup
of the Stereoblend characteristics which is programmable in a wide range is described in
Section 8.8.
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