Description of the audioprocessor

TDA7418

12/29

4

Description of the audioprocessor

4.1

Input stages

In the basic configuration, one stereo pseudo differential (programmable as single-ended

input) and three single-ended stereo inputs are available.

Pseudo differential stereo input (PD/SE4)

The PD input is implemented as a buffered pseudo differential stereo stage with 100k

Ω

input-impedance at each input. The attenuation is fixed to -3dB in order to adapt the

incoming signal level. It is also configurable as single-ended input.

Single-ended stereo input (SE1, SE2, SE3)

The input-impedance at each input is 100k

Ω and the attenuation is fixed to -3dB for

incoming signals.

Figure 3.

Input stage

4.2

AutoZero

The AutoZero allows a reduction of the number of pins as well as external components by

canceling any offset generated by or before the In-Gain-stage (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 input source is changed and needs max. 0.6ms

for the alignment. To avoid audible clicks the Audio processor is muted before the loudness

stage during this time.

AutoZero-remain

In some cases, for example if the µP 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

QD/SE4

QD_L/SE4_L

QD_R/SE4_R

QD_G

SE3

SE2

SE2_L

SE2_R

QD/SE4

SE1

SE2

SE3

Input

Selector

In Gain

SE1

SE1_L

SE1_R

SE3_L

SE3_R