TDA7541B Datasheet, PDF (32/77 Pages) STMicroelectronics – AM/FM car radio tuner IC with stereo decoder and intelligent selectivity system

Functional description
TDA7541B
4.2.1
rectifier is programmable (AINBT). A comparator activates a pulse generator. The duration
of this pulse is software programmable (AINT) and is smooth blanking out the spikes in mixer2.
Usage of control bit ADSEL (Addr23D7)
The control bit ADSEL can be used to increase the selectivity of the application in AM mode
and WB mode. In FM it has no function. Table 12 shows the functionality of the control bit.
Table 13. Usage of ADSEL
FMON WBON ADSEL
Addr4D7 Addr11D1 Addr23D7
Note
1
0
X
Standard FM mode
1
1
Weather band mode using 450 kHz ceramic filter;
ISS filter must be manually switched on in order to limit the band
0
width at 450 kHz IF (ISSENA/ISSON = "1");
450 kHz ceramic filter is switched in series to ISS filter to
increase selectivity
1
1
0
0
Standard weather band mode;
1
ISS filter must be manually switched on in order to limit the band
width at 450 kHz IF (ISSENA/ISSON = "1")
0
Standard AM mode
0
0
AM mode using ISS filter;
1
ISS filter (22 kHz band width) is switched in series to the 450 kHz
ceramic filter
0
1
X
Not allowed
4.3
4.3.1
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Stereo decoder
Decoder
The stereo decoder-part of the TDA7541B contains all functions necessary to demodulate
the MPX-signal, like pilot tone-dependent MONO/STEREO switching as well as the stereo
blend and high cut.
Adaptations like programmable input gain, roll-off compensation, selectable de-emphasis
time constant and a programmable field strength input allow easy adoption to different
applications.
The 4^th order input filter has a corner frequency of 80 kHz and is used to attenuate spikes
and noise and acts as an anti-aliasing filter for the following switch capacitor filters.
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 canceled. For reaching a high channel separation
the TDA7541B offers an I²C bus programmable roll-off adjustment, which is able to
compensate the low pass behavior of the tuner section. Within the compensation range an
adjustment to obtain about 40 dB channel separation is possible. The bits for this
adjustment are located together with the level gain adjustment in one byte. This gives the
Doc ID 16048 Rev 1