TDA7402_07 STMICROELECTRONICS [STMicroelectronics], TDA7402_07 Datasheet - Page 47

• Manufacturer Part Number: TDA7402_07
• Description: Car radio signal processor
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

TDA7402
8
8.1
Functional description of the multipath detector
Using the multipath detector the audible effects of a multipath condition can be minimized. A
multipath condition is detected by rectifying the spectrum around 19kHz in the fieldstrength
signal. An external capacitor is used to define the attack and decay times for the stereo
blend (see block diagram,
should be a low leakage current type (e.g ceramic). Using this configuration an adaptation to
the user's requirement is possible without effecting the "normal" fieldstrength input (level) for
the stereo decoder. This application is given in
used to control the Highcut through the multipath detector
Selecting the "internal influence" in the configuration byte the stereo-blend and/or the
highcut is automatically invoked during a multipath condition according to the voltage
appearing at the MP_OUT pin.
Figure 35. Block diagram of the multipath detector
Quality detector
The A619 offers a quality detector output which gives a voltage representing the FM
reception conditions. To calculate this voltage the MPX-noise and the multipath-detector
output are summed according to the following formula :
V
The noise-signal is the PEAK signal without additional influences (see the noiseblanker
description). The factor 'a' can by programmed to 0.7 .... 1.15. The output is a low
impedance output able to drive external circuitry as well as simply fed to an AD converter for
RDS applications.
LEVEL
MP_IN
Qual
= 1.6 (V
BANDPASS
GAIN 2 bits
LOWPASS
53KHz
19KHz
Noise
-0.8 V)+ a (REF5V-V
RECTIFIER
GAIN 2 bits
LOWPASS
High-Cut-Infl.
Attach<500μs
Decay=2/10ms
2.2KHz
Figure
MP HOLD
34). Due to the very small charge currents this capacitor
0 ... 1.5V
SHIFT
VDD
Mpout
Functional description of the multipath detector
=
).
Figure
0.25μA/0.5μA
CHARGE
34. Another (internal) time constant is
VDD
LOWPASS
=
100Hz
D00AU1166
VDD
=
300μA
CHARGE
FAST
470nF
MP_OUT
INFLUENCE
INFLUENCE
INT.
INT.
Stereoblend-Infl.
Attach=1ms
Decay=4/8s
to HCC
to SB
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