TDA7411 Datasheet, PDF (25/43 Pages) STMicroelectronics – ADVANCED CAR SIGNAL PROCESSOR

TDA7411
The gain can be programmed through 4 bits in the "Stereo Decoder Adjustment"-byte. The MONO-voltage
VMO (0dB channel separation) can be chosen selecting VSBL.
All necessary internal reference voltages like REF5V are derived from a bandgap circuit. Therefore they
have a temperature coefficient near zero. This is useful if the fieldstrength signal is also temperature com-
pensated. But most of the IF-devices are applying a LEVEL-voltage with a TC of 3300ppm. The A673 of-
fers this TC for the reference voltages, too. The TC is selectable with bit D₇ of the "stereo decoder
adjustment"-byte.
Figure 20. Relation Between Internal and External LEVEL Voltages and Setup of Stereoblend
INTERNAL
VOLTAGES
REF 5V
SETUP OF VST
LEVEL INTERN
INTERNAL
VOLTAGES
REF 5V
SETUP OF VMO
LEVEL INTERN
VSBL
LEVEL
VSBL
58%
29%
VMO
VST
t
FIELDSTRENGHT VOLTAGE
modAU639
VMO
t
VST
FIELDSTRENGHT VOLTAGE
Highcut Control
The highcut control set-up is similar to the stereoblend control set-up: the starting point VHCH can be set
with 2 bits to be 42, 50, 58 or 66% of REF5V whereas the range can be set to be 17, 22, 28 or 33% of
VHCH (see fig. 21).
Figure 21. High cut characteristics
LOWPASS
TIME CONSTANT
3•τ_Deemp
τ_Deemp
VHCL
VHCH FIELDSTRENGHT
D97AU640
Functional Description of the Noise Blanker
In the automotive environment spikes produced by the ignition and for example the wiper-motor disturb
the MPX-signal. The aim of the noise blanker part is to cancel the audible influence of the spikes. There-
fore the output of the stereo decoder is held at the actual voltage for a time between 22 and 38µs (pro-
grammable). The block diagram of the noise blanker is given in fig.22
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