TDA7406 datasheet(35/64 Pages) STMICROELECTRONICS

35 / 64 page

TDA7406

Functional Description of Stereodecoder

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Functional Description of Stereodecoder

Figure 23.

Block diagram of the stereodecoder

The stereodecoder-part of the TDA7406 (see Fig. 25) contains all functions necessary to

demodulate the MPX-signal like pilot tone-dependent MONO/STEREO-switching as well as

“stereoblend” and “highcut”. Adaptations like programmable input gain, roll-off

compensation, selectable de-emphasis time constant and a programmable field strength

input allow to use different IF-devices.

8.1

Stereodecoder-Mute

The TDA7406 has a fast and easy to control RDS-Mute function which is a combination of

the audioprocessor's SoftMute and the high-ohmic mute of the stereodecoder. If the

stereodecoder is selected and a SoftMute command is sent (or activated through the SM-

pin) the stereodecoder will be set automatically to the high-ohmic mute condition after the

audio-signal has been soft muted. Hence a checking of alternate frequencies could be

performed. Additionally the PLL can be set to “Hold”-mode, which disables the PLL input

during the mute time. To release the system from the mute condition simply the unmute-

command must be sent: the stereodecoder is unmuted immediately and the audioprocessor

is softly unmuted. Figure 28 shows the output-signal VO as well as the internal

stereodecoder mute signal. This influence of SoftMute on the stereodecoder mute can be

switched off by setting bit 3 of the SoftMute byte to “0”. A stereodecoder mute command (bit

0, stereodecoder byte set to “1”) will set the stereodecoder in any case independently to the

high-ohmic mute state.

If any other source than the stereodecoder 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. No further mute command should be applied.

TDA7406 Datasheet(PDF) 35 Page - STMicroelectronics