TDA7407D STMicroelectronics, TDA7407D Datasheet - Page 30

• Manufacturer Part Number: TDA7407D
• Description: IC PROCESSOR ADV SIGNAL 44-LQFP
• Manufacturer: STMicroelectronics
• Type: Car Signal Processorr

Specifications of TDA7407D

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

Multipath detector
5.2.11
5.2.12
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Trigger path
The block diagram of the noiseblanker is given in
In the first stage the spikes must be detected but to avoid wrong triggering on high
frequency (white) noise, a complex trigger control is implemented. Behind the trigger stage
a pulse former generates the "blanking" pulse. To avoid any crosstalk to the signal path the
noiseblanker is supplied by his own biasing circuit.
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 140kHz increases the PEAK voltage. The resulting voltage can be adjusted
by use of the noise rectifier discharge current.
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 selected duration.
Figure 23. Block Diagram of the Noiseblanker
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.
a)
b)
the low threshold in 8 steps (bits D0 to D2 of the noiseblanker byte)
the noise adjusted threshold in 4 steps (bits D3 and D4 of the noiseblanker byte,
see
MPX
MPX
Figure
23).
RECTIFIER
D98AU856
CONTROL
LOWPASS
RECT
+
+
+
PEAK
-
VTH
Figure
23.
GENERATOR
THRESHOLD
THRESHOLD
ADDITIONAL
MONOFLOP
CONTROL
HOLDN
TDA7407