TDA7404 ST Microelectronics, TDA7404 Datasheet - Page 9

• Manufacturer Part Number: TDA7404
• Description: CARRADIO-SIGNAL-PROCESSOR
• Manufacturer: ST Microelectronics

before the Mixing-block to eliminate all offsets generated by the Input-Stages and the In-Gain (Please notice
that externally generated offsets, e.g. generated through the leakage current of the coupling capacitors, are not
canceled).
The auto-zeroing is started every time the DATA-BYTE 0 (Input Selector/Gain) is selected and takes a time of
max. 0.3ms. To avoid audible clicks the Audioprocessor is muted before the loudness stage during this time.
1.2.1 AutoZero-Remain
In some cases, for example if the uP is executing a refresh cycle of the IIC-Bus-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 TDA7404D could be switched in the AutoZero-Remain-Mode (I2 bit 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.
1.3 Mixing Stage
The 4 step Mixing stage offers the possibility to mix the rear selector signal or the phone signal to any other
source. Due to the fact that the mixing-stage is located behind the In-Gain-stage fine adjustments of the main
source level could be done in this way.
Figure 2. Signal-Flow of Mixing-Stage
1.4 Loudness
There are four parameters programmable in the loudness stage:
1.4.1 Attenuation
Figure 3 shows the attenuation as a function of frequency at f
D i f f i n
S E 1
S E 2
S E 3
M o n o
B e e p
I n p u t S e l e c t o r
I n - G a i n
C
2 5
k
= 400Hz.
-3.5dB
- 6dB /
- 12dB
I n p u t / B e e p o r M o n o
0dB
M i x i n g L e v e l
/
/
/
- 6dB
-100dB
- 9.6dB
- 2.5dB
M i x i n g
TDA7404D
L o u d n e s s
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