TDA7411 ST Microelectronics, TDA7411 Datasheet - Page 24

• Manufacturer Part Number: TDA7411
• Description: ADVANCED CAR SIGNAL PROCESSOR
• Manufacturer: ST Microelectronics

TDA7411
dently of the absolute voltage range between the VHCH- and VHCL-values.
The highcut function can be switched off by I2C-bus (bit D7, Field strength byte set to "0").
The setup of the highcut characteristics is described in 2.9.
PLL and Pilot tone-Detector
The PLL has the task to lock on the 19kHz pilot tone during a stereo-transmission to allow a correct de-
modulation. The included pilot tone-detector enables the demodulation if the pilot tone reaches the select-
ed pilot tone threshold V
A673 via I
Field Strength Control
The field strength input is used to control the highcut- and the stereoblend-function. In addition the signal
can be also used to control the noise blanker thresholds and as input for the multipath detector.
LEVEL-Input and -Gain
To suppress undesired high frequency modulation on the highcut- and stereoblend-function the LEVEL
signal is low pass filtered firstly. The filter is a combination of a 1.st-order RC-low pass at 53kHz (working
as anti-aliasing filter) and a 1.st-order switched capacitor low pass at 2.2kHz. The second stage is a pro-
grammable gain stage to adapt the LEVEL signal internally to different IF-devices (see test mode section
5: LEVELINTERN). The gain is widely programmable in 16 steps from 0dB to 10dB (step=0.67dB). These
4 bits are located together with the Roll-Off bits in the "Stereo decoder-Adjustment"-byte to simplify a pos-
sible adaptation during the production of the car radio.
Stereoblend Control
The stereoblend control block converts the internal LEVEL-voltage (LEVELINTERN) into a demodulator
compatible analog signal, which is used to control the channel separation between 0dB and the maximum
separation. Internally this control range has a fixed upper limit, which is the internal reference voltage
REF5V. The lower limit can be programmed between 29.2 and 58% of REF5V in 4.167% steps (see
figs.19, 20).
To adjust the external LEVEL-voltage to the internal range two values must be defined: the LEVEL gain
L
LEVEL gain LG has to be defined. The following equation can be used to estimate the gain:
Figure 19. Internal stereo blend characteristics
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G
and VSBL (see fig. 20). To adjust the voltage where the full channel separation is reached (VST) the
2
C-bus the detector output (signal STEREO, see block diagram) can be checked.
PTHST
. Two different thresholds are available. By reading the status byte of the
L
G
=
-------------------------------------------------------------------------------------- -
Field strenght voltage [STEREO]
R EF5 V