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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

1.4 Loudness

There are four parameters programmable in the loudness stage:

1.4.1 Attenuation

Diffin

Loudness

SE1

SE2

SE3

Mono

25

k

Beep

Input Selector

In-Gain

Mixing

Mixing Level

Input / Beep or Mono

0dB

/

-100dB

-3.5dB

/

- 9.6dB

-

6dB

/

-

6dB

- 12dB

/

- 2.5dB