AS3412 datasheet(12/85 Pages) AMSOSRAM

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Page 11

[v1-00] 2016-Apr-06

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AS3412 − Detailed Description

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), an internal state machine reduces

the microphone gain automatically. For some designs it might

be useful to switch off this feature. Especially in feed-back

systems very often infrasound can cause an overload condition

of the microphone preamplifier which results in low frequency

noise. This behavior can be avoided by disabling the AGC

function.

Input Capacitor Selection

The microphone preamplifier needs one bias resistor (RBias) per

channel as well as DC blocking capacitors (CMIC). The capacitors

CAC are DC blocking capacitors to avoid DC amplification of the

non-inverting microphone preamplifier. This capacitor has an

influence on the frequency response because the internal

feedback resistors create a high pass filter together with the

capacitor CAC. The typical application circuit is shown in

Figure 11 with all necessary components.

Figure 11:

Microphone Capacitor Selection Circuit

Microphone Capacitor Selection Circuit: This diagram shows a typical microphone application circuit with all

necessary components to operate the amplifier.

MUTE

MUTE_MIC_LEFT

MUTE

MUTE_MIC_RIGHT

AGC

MICL

MICR

MICACL

MICACR

QMICL

QMICR

CMIC

RBIAS

RMICIN

CAC

MICS

ANC Microphone

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