E-TDA7461ND View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'E-TDA7461ND' PDF : 48 Pages View PDF
TDA7461
Stereo decoder part
All necessary internal reference voltages like REF5V are derived from a band gap circuit.
Therefore they have a temperature coefficient near zero. This is useful if the fieldstrength
signal is also temperature compensated.
But most IF devices apply a LEVEL voltage with a TC of 3300 ppm. The TDA7461 offers this
TC for the reference voltages, too. The TC is selectable with bit D7 of the “stereo decoder
adjustment" byte.
Figure 23. Relation between internal and external LEVEL voltage and setup of
Stereo blend
INTERNAL
VOLTAGES
REF 5V
VSBL
SETUP OF VST
LEVEL INTERN
INTERNAL
VOLTAGES
REF 5V
LEVEL
58%
50%
VSBL 42%
33%
SETUP OF VMO
LEVEL INTERN
VMO
VST
t
FIELDSTRENGHT VOLTAGE
D97AU639
VMO
t
VST
FIELDSTRENGHT VOLTAGE
4.5.9
High cut control
The high cut control setup is similar to the stereo blend 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 Figure 24).
Figure 24. High cut characteristics
LOWPASS
TIME CONSTANT
3•τDeemp
τDeemp
VHCL
D97AU640
VHCH FIELDSTRENGHT
4.6
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 noise blanker part is to cancel the
audible influence of the spikes. Therefore the output of the stereo decoder is held at the
actual voltage for 40 µs.
In a first stage the spikes must be detected but to avoid a 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
noise blanker is supplied by his own biasing circuit.
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