TDA7406 datasheet(36/64 Pages) STMICROELECTRONICS

36 / 64 page

Functional Description of Stereodecoder

TDA7406

36/64

Figure 24.

Signals during stereodecoder's SoftMute

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 1Vrms

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.

TDA7406 データシート(PDF) 36 Page - STMicroelectronics