TDA7404D Datasheet, PDF (9/26 Pages) STMicroelectronics – CARRADIO-SIGNAL-PROCESSOR

TDA7404D
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
Input Selector
In-Gain
Mixing
Diffin
SE1
SE2
SE3
Mono
Beep
Mixing Level
25k Input / Beep or Mono
0dB /
-3.5dB /
- 6dB /
- 12dB /
-100dB
- 9.6dB
- 6dB
- 2.5dB
Loudness
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_C = 400Hz.
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