TDA7541B datasheet(32/77 Pages) STMICROELECTRONICS

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Functional description

TDA7541B

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Doc ID 16048 Rev 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.

4.2.1

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.

4.3

Stereo decoder

4.3.1

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 4th 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

Table 13.

Usage of ADSEL

FMON

WBON

ADSEL

Note

Addr4D7 Addr11D1 Addr23D7

Standard FM mode

Weather band mode using 450 kHz ceramic filter;

ISS filter must be manually switched on in order to limit the band

width at 450 kHz IF (ISSENA/ISSON = "1");

450 kHz ceramic filter is switched in series to ISS filter to

increase selectivity

Standard weather band mode;

ISS filter must be manually switched on in order to limit the band

width at 450 kHz IF (ISSENA/ISSON = "1")

Standard AM mode

AM mode using ISS filter;

ISS filter (22 kHz band width) is switched in series to the 450 kHz

ceramic filter

Not allowed

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