TDA7407 datasheet(27/46 Pages) STMICROELECTRONICS

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TDA7407

Multipath detector

27/46

Figure 19.

Signals during stereo decoder's softmute

Figure 20.

Internal Stereoblend characteristics

If any other source than the stereo decoder is selected the decoder remains muted and the

MPX pin is connected to Vref to avoid any discharge of the coupling capacitor through

leakage currents.

5.2.2

Ingain + Infilter

The Ingain stage allows to adjust the MPX signal to a magnitude of about 1Vrms internally

which is the recommended value. The 4th order input filter has a corner frequency of 80KHz

and is used to attenuate spikes and nose and acts as an anti allasing filter for the following

switch capacitor filters.

5.2.3

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 TDA7407 offers an I2C bus programmable roll-off adjustment which is able to

compensate the lowpass behaviour of the tuner section. If the tuner attenuation at 38kHz is

in a range from 4.2% to 31.0% the TDA7407 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.

SOFTMUTE

COMMAND

STD MUTE

D97AU638

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

012

LEVELINTERN [V]

CS [dB]

345

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