TDA7407 STMicroelectronics, TDA7407 Datasheet - Page 21

• Manufacturer Part Number: TDA7407
• Description: IC PROCESSOR CAR SIGNAL 44TQFP
• Manufacturer: STMicroelectronics
• Type: Car Signal Processorr

Specifications of TDA7407

• Applications: Automotive Audio
• Mounting Type: Surface Mount
• Package / Case: 44-LQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: 497-3979

TDA7407
5.1
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
Description of the audioprocessor part
Input multiplexer
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Input stages
Most of the input stages have remained the same as in preceeding ST audioprocessors with
the exception of the CD inputs (see
on the market having a significant high source impedance which strongly affects the
common mode rejection of the normal differential input stage. The additional buffer of the
CD input avoids this drawback and offers the full common mode rejection even with those
CD players.
The output of the CD stage is permanently available of the CD out-pins
AutoZero
In order to reduce the number of pins, there is no AC coupling between the In-Gain and the
following stage, so that any offset generated by or before the In-Gain stage would be
transferred or even amplified to the output. To avoid that effect a special offset cancellation
stage called AutoZero is implemented.
This stage is located before the volume block to eliminate all offsets generated by the stereo
decoder, the input stage and the In-Gain (please notice that externally generated offsets,
e.g. generated through the leakage current of the coupling capacitors, are not cancelled).
Auto-zeroing is started every time the DATA-BYTE 0 is selected and takes a time of max.
0.3ms. To avoid audible clicks the audioprocessor is muted before the volume stage during
this time.
AutoZero remain
In some cases, for example if the μP is executing a refresh cycle of the I
programming, it is not useful to start a new AutoZero action because no new source is
selected and an undesired mute would appear at the outputs. For such applications the
TDA7407 could be switched in the "Auto Zero Remain mode" (Bit 6 of the subaddress byte).
If this bit is set to high, the DATABYTE 0 could be loaded without invoking the AutoZero and
the old adjustment value remains.
Multiplexer output
The output signal of the input multiplexer is available at separate pins (please see the block
diagram). This signal represents the input signal amplifier by the In-Gain stage and is also
going into the mixer stage.
CD quasi differential
Cassette stereo
Phone differential
AM mono
Stereo decoder input.
Figure
7). In the meantime there are some CD players
2
Multipath detector
C bus
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