TDA7460NDTR(2009) View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

TDA7460NDTR
(Rev.:2009)

Car radio signal processor

STMicroelectronics 

TDA7460ND

Stereo decoder part

5.5

Description of stereo decoder

The stereo decoder part of the TDA7460ND (see Figure 20.) contains all functions

necessary to demodulate the MPX signal like pilot tone dependent mono/stereo switching

as well as "stereo blend" and "high cut" functions.

Adaptations like programmable input gain, roll-off compensation, selectable de-emphasis

time constant and a programmable fieldstrength input allow to use different IF devices.

Figure 21. Block diagram of the stereo decoder

DEMODULATOR

DEEMPHASIS

bsolete Product(s) MPX

100K

INGAIN

3.5 ... 11dB

STEP 2.5dB

INFILTER

LP 80KHz

4.th ORDER

PLL +

PILOT-DET.

F19

F38

STEREO

NOISE BLANKER

HOLDN

D97AU762

- PLOT CANC

- ROLL-OFF COMP.

- LP 25KHz

+ HIGHCUT

t=50 or 75μs

FM_L

FM_R

SB CONTROL

REF 5V

VSBL

HC

CONTROL

D

A

VHCCH

VHCCL

MPINFL

LEVEL INPUT

LEVEL INTERN

LP 2.2KHZ

-

1.th ORDER

LEVEL

GAIN 0..10dB

MULTIPATH

DETECTOR

MPIN

MPOUT

Obsolete Product(s) - O 5.5.1

Stereo decoder mute

The TDA7460ND has a fast and easy to control RDS mute function which is a combination

of the audioprocessor soft mute and the high-ohmic mute of the stereo decoder. If the stereo

decoder is selected and a soft mute command is sent (or activated through the SM pin) the

stereo decoder will be set automatically to the high-ohmic mute condition after the audio

signal has been softmuted.

Hence a checking of alternate frequencies could be performed. To release the system from

the mute condition simply the unmute command must be sent: the stereo decoder is

unmuted immediately and the audioprocessor is softly unmuted. Fig. 18 shows the output

signal VO as well as the internal stereo decoder mute signal. This influence of Softmute on

the stereo decoder mute can be switched off by setting bit 3 of the Softmute byte to "0". A

stereo decoder mute command (bit 0, stereo decoder byte set to "1") will set the stereo

decoder in any case independently to the high-ohmic mute state.

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.

27/49

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