參數(shù)資料
型號(hào): TDA7404D
廠商: STMICROELECTRONICS
元件分類: 音頻控制
英文描述: 1 CHANNEL(S), TONE CONTROL CIRCUIT, PDSO28
封裝: SOP-28
文件頁數(shù): 6/35頁
文件大小: 633K
代理商: TDA7404D
Description of functionality
TDA7404
4.2
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 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.
4.2.1
AutoZero remain
In some cases, for example if the P 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
TDA7404 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.
4.3
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 4.
Signal-flow of mixing-stage
Diffin
Loudness
SE1
SE2
SE3
Mono
25k
Beep
Input Selector
In-Gain
Mixing
Mixing Level
Input / Beep or Mono
0dB
/
-100dB
-3.5dB
/
- 9.6dB
- 6dB /
- 6dB
- 12dB
/
- 2.5dB
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