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參數(shù)資料
| 型號： | TDA7403 |
| 廠商： | 意法半導體 |
| 英文描述： | BASIC SIGNAL PROCESSOR |
| 中文描述： | 基本信號處理器 |
| 文件頁數(shù)： | 16/26頁 |
| 文件大小： | 195K |
| 代理商： | TDA7403 |
Highcut Control
The highcut control setup is similar to the
stereoblend control setup : the starting point
VHCH can be set with 2 bits to be 42, 50, 58 or
66% of REF5V whereas the range can be set to
be 17 or 33% of VHCH(see fig. 20).
FUNCTIONAL DESCRIPTION OF THE NOISE-
BLANKER
In the automotive environment the MPX signal is
disturbed by spikes produced by the ignition and
for example the wiper motor. The aim of the
noiseblanker part is to cancel the audible influ-
ence of the spikes. Therefore the output of the
stereodecoder is held at the actual voltage for
40
μ
s.
In a first stage the spikes must be detectedbut to
avoid a wrong triggering on high frequency
(white) noise a complex trigger control is imple-
mented. Behind the triggerstage a pulse former
generates the ”blanking” pulse. To avoid any
crosstalk to the signalpath the noiseblanker is
suppliedby his own biasing circuit.
TriggerPath
The incoming MPX signal is highpass filtered,
amplified and rectified. This second order high-
pass-filter has a cornerfrequency of 140kHz. The
rectified signal, RECT, is lowpass filtered to gen-
erate a signal called PEAK. Also noise with a fre-
quency 140kHz increases the PEAK voltage. The
PEAK voltage is fed to a threshold generator,
which adds to the PEAK voltage a DC depend-
ent threshold VTH. Both signals, RECT and
PEAK+VTH are fed to a comparator which trig-
gers a re-triggerable monoflop. The monoflop’s
output activates the sample-and-hold circuits in
the signalpathfor 40
μ
s.
The block diagram of the noiseblanker is given in
fig.20.
Automatic Noise Controlled Threshold Adjust-
ment (ATC)
There are mainly two independentpossibilities for
programmingthe trigger threshold:
a the low thresholdin 8 steps(bits D0 to D2 of
the noiseblankerbyte)
b the noise adjusted thresholdin 4 steps
(bits D3 andD4 of the noiseblankerbyte,
see fig. 13).
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 op-
eration is high.
If the MPX signal is noisy the PEAK voltage in-
creases due to the higher noise, which is also
rectified. With increasing of the PEAK voltage the
trigger threshold increases, too.
gain is programmable in 4 steps(see fig. 13).
This particular
LOWPASS
TIME CONSTANT
D97AU640
τ
Deemp
FIELDSTRENGHT
VHCH
VHCL
3
τ
Deemp
Figure 20. Highcut characteristics
+
-
RECTIFIER
LOWPASS
RECT
+
+
THRESHOLD
GENERATOR
VTH
PEAK
ADDITIONAL
THRESHOLD
CONTROL
MONOFLOP
HOLDN
MPX
D98AU861
HIGH PASS
Figure 21. Block diagram of the noiseblanker
TDA7403
16/26
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相關(guān)代理商/技術(shù)參數(shù) |
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| TDA7403_02 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:BASIC SIGNAL PROCESSOR |
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| TDA7404 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:CARRADIO-SIGNAL-PROCESSOR |
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