TDA7460ND STMicroelectronics, TDA7460ND Datasheet - Page 31

• Manufacturer Part Number: TDA7460ND
• Description: IC PROCESSOR CAR RAD SGNL SO-20
• Manufacturer: STMicroelectronics
• Type: Car Signal Processorr

Specifications of TDA7460ND

• Applications: Automotive Systems
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

TDA7460ND
5.6.1
5.6.2
5.6.3
Trigger path
The incoming MPX signal is highpass filtered, amplified and rectified. This second order
highpass-filter has a corner frequency of 140kHz. The rectified signal, RECT, is lowpass
filtered to generate a signal called PEAK. Also noise with a frequency 140 kHz increases the
PEAK voltage. The PEAK voltage is fed to a threshold generator, which adds to the PEAK
voltage a DC dependent threshold VTH. Both signals, RECT and PEAK+VTH are fed to a
comparator which triggers a re-triggerable monoflop. The monoflop's output activates the
sample-and-hold circuits in the signal path for 40 μs.
The block diagram of the noise blanker is given in
Figure 26. Block diagram of the noise blanker
Automatic noise controlled threshold adjustment (ATC)
There are mainly two independent possibilities for programming the trigger threshold:
The low threshold is active in combination with a good MPX signal without any noise; the
PEAK voltage is less than 1V. The sensitivity in this operation is high.
If the MPX signal is noisy the PEAK voltage increases due to the higher noise, which is also
rectified. With increasing of the PEAK voltage the trigger threshold increases, too. This
particular gain is programmable in 4 steps (see
Automatic threshold control
Besides the noise controlled threshold adjustment there is an additional possibility for
influencing the trigger threshold. It is depending on the stereo blend control.
The point where the MPX signal starts to become noisy is fixed by the RF part. Therefore
also the starting point of the normal noise-controlled trigger adjustment is fixed (fig. 16). In
some cases the behavior of the noise blanker can be improved by increasing the threshold
even in a region of higher fieldstrength. Sometimes a wrong triggering occurs for the MPX
signal often shows distortion in this range which can be avoided even if using a low
threshold.
Because of the overlap of this range and the range of the stereo/mono transition it can be
controlled by stereo blend. This threshold increase is programmable in 3 steps or switched
off with bits D0 and D1 of the fieldstrength control byte.
MPX
a)
b)
the low threshold in 8 steps (bits D0 to D2 of the noise blanker byte)
the noise adjusted threshold in 4 steps (bits D3 and D4 of the noise blanker byte,
see
HIGH PASS
Figure
17.).
RECTIFIER
D98AU861
LOWPASS
RECT
Figure
Figure 26.
+
+
17.).
+
PEAK
-
VTH
GENERATOR
THRESHOLD
THRESHOLD
ADDITIONAL
MONOFLOP
CONTROL
Stereo decoder part
HOLDN
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