TDA7402 STMicroelectronics, TDA7402 Datasheet - Page 40

• 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
5.4
5.5
5.6
5.7
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the channel separation and the fieldstrength control are trimmed. The setup of the stereo
blend characteristics which is programmable in a wide range is described in
De-emphasis and highcut
The de-emphasis lowpass allows to choose a time constant between 37.5 and 100µs. The
highcut control range will be 2 x τ
constant (see programming section). The bit D7 of the hightcut-byte will shift timeconstant
and range.
Inside the highcut control range (between VHCH and VHCL) the LEVEL signal is converted
into a 5 bit word which controls the lowpass time constant between τ
Thereby the resolution will remain always 5 bits independently of the absolute voltage range
between the VHCH and VHCL values. In addition the maximum attenuation can be fixed
between 2 and 10dB.
The highcut function can be switched off by I
The setup of the highcut characteristics is described in
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 demodulation. The included pilot tone-detector enables the demodulation if the pilot
tone reaches the selected pilot tone threshold V
available. The detector output (signal STEREO, see
checked by reading the status byte of the TDA7402 via I
can be set into "Hold"-mode which freezes the PLL's state (bit D
releasing the Soft Mute the PLL will again follow the input signal only by correcting the
phase error.
Fieldstrength control
The fieldstrength input is used to control the highcut and the stereo blend function. In
addition the signal can be also used to control the noiseblanker thresholds and as input for
the multipath detector. These additional functions are described in sections
EVEL input and gain
To suppress undesired high frequency modulation on the highcut- and stereo blend-control
signal the LEVEL signal is lowpass filtered firstly. The filter is a combination of a 1st order
RC lowpass at 53kHz (working as anti-aliasing filter) and a 1st-order switched capacitor
lowpass at 2.2kHz. The second stage is a programmable gain stage to adapt the LEVEL
signal internally to different IF devices (see Testmode section 5: LEVELHCC). The gain is
widely programmable in 16 steps from 0dB to 6dB (step=0.4dB). These 4 bits are located
together with the Roll-Off bits in the "Stereo decoder adjustment" byte to simplify a possible
adjustment during the production of the car radio. This signal controls directly the Highcut
stage whereas the signal is filtered again (fc=100Hz) before the stereo blend stage
(see
Figure
35).
Deemp
or 2.7 x τ
2
C bus (bit D
PTHST
Deemp
Figure 2: Block
. Two different thresholds are
dependent on the selected time
Chapter
2
C-bus. During a Soft Mute the PLL
7
, Highcut byte set to "0").
5.9.
4
, Soft Mute byte). After
Deemp
diagram) can be
...3 (3.7) x τ
5.3
Chapter
and 6.
TDA7402
Deemp
5.8.
.