TDA7402 STMicroelectronics, TDA7402 Datasheet - Page 38

• Manufacturer Part Number: TDA7402
• Description: IC PROCESSOR CAR SIGNAL 44-LQFP
• Manufacturer: STMicroelectronics
• Type: Car Signal Processorr

Specifications of TDA7402

• Applications: Automotive Systems
• Mounting Type: Surface Mount
• Package / Case: 44-LQFP
• Case: QFP
• Dc: 05+
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Functional description of stereo decoder
5
Figure 28. Block diagram of stereo decoder
5.1
38/69
AM-IF
MPX
AM
100K
100K
Functional description of stereo decoder
The stereo decoder-part of the TDA7402 (see
demodulate the MPX-signal like pilot tone dependent Mono/Stereo switching as well as
"stereo blend" and "highcut". Adaptations like programmable input gain, roll off
compensation, selectable de-emphasis time constant and a programmable fieldstrength
input allow to use different IF devices.
Stereo decoder mute
The TDA7402 has a fast and easy to control RDS mute function which is a combination of
the audioprocessor's 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.
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 stereo decoder is unmuted immediately and the audioprocessor is softly
unmuted.
signal. This influence of Soft Mute on the stereo decoder mute can be switched off by setting
bit 3 of the Soft Mute byte to "0". A stereo decoder mute command (bit 0, stereo decoder
byte set to "1") will also set the stereo decoder 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 V
leakage currents. No further mute command should be applied.
D00AU1135
3.5 ... 11dB
STEP 2.5dB
Figure 29
INGAIN
shows the output-signal V
NOISE BLANKER
LP 80KHz
4.th ORDER
PILOT-DET.
INFILTER
NOISE
ref
PLL +
STEREO
HOLDN
to avoid any discharge of the coupling capacitor through
F19
F38
- PLOT CANC
- ROLL-OFF COMP.
- LP 25KHz
DEMODULATOR
Figure
O
as well as the internal stereo decoder mute
SB CONTROL
MP-IN
MPSBOUT
MULTIPATH DET.
-
28) contains all functions necessary to
MPHCOUT
MP-OUT
MPSBINFL
REF 5V
VSBL
MPHCINFL
t=50.62..5.75,100μs
(37.5,47,56,75μs)
DEEMPHASIS
+ HIGHCUT
CONTROL
D
HC
-
5 bits
A
LEVELSB-LP
LEVELHC-LP
LEVEL INPUT
DETECTOR
QUALITY
GAIN 0..6dB
VHCCH
VHCCL
+
FM_L
FM_R
TDA7402
LEVEL
QUAL