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AS3418

Functional Description

Datasheet

• PUBLIC

DS000507

• v4-00 • 2020-Jan-23

│ 13

Figure 8:

Parameter of Line Input

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

VLIN

Input Signal Level

VBAT*

0.9

VBAT

VPEAK

RLIN

Input Impedance

Ω

AMUTE

Mute Attenuation

100

6.2

Microphone Inputs

The AS3418 offers two low noise microphone inputs with full digital control and a dedicated DC offset

cancellation pin for each microphone input. In total each gain stage offers up to 63 gain steps of 0.5dB

resulting in a gain range from 0dB to +31dB. The microphone gain is stored digitally during production,

in an EEPROM memory on the ANC chip. Besides the standard microphone gain register for left and

right channel, the chip features also four additional microphone gain registers for Monitor- and

Playback Only operation mode. Thus, in Monitor/Playback Only mode, a completely different gain

setting for left and right microphone can be selected to implement voice filter functions in order to

amplify the speech band for better intelligibility.

Figure 9:

Stereo Microphone Inputs

To avoid unwanted start-up pop noise, a soft-start function is implemented for an automatic gain

ramping of the device. In case of an overload condition on the microphone input (e.g. high sound

pressure level) there is also an automatic gain control (AGC) function available which reduces the gain

to a moderate level. For some designs it might be useful to switch off this feature. Especially in feed-

back systems infrasound can cause an overload condition of the microphone preamplifier that results

in low frequency noise which can be avoided by disabling the AGC.

MUTE

AGC

MICL

MICR

MICACL

MICACR

QMICL

QMICR

AGC

DISCHARGE

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