AS3658F-BCTP datasheet(106/158 Pages) AMSCO

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AS3658

Data Sheet Confidential - Detail ed Descri ption- Audio Functi ons

9.8

Microphone Input

General

The audio front-end offers one microphone inputs and a low noise microphone voltage supply (microphone bias), voice

activation, microphone connect detection and push button remote control.

Figure 49. Microphone Input Block diagram and External Circuit

Gain Stage & Limiter

The integrated pre-amplifier allows 3 preset gain settings. There is also a limiter which attenuates high input signals

from e.g. electret microphones signal to 1Vp. The AGC has 15 steps with a dynamic range of about 29dB. The AGC is

ON by default but can be disabled by a microphone register bit.

Apart from the microphone pre-amplifier the microphone input signal can further be amplified with 32 @1.5dB

programmable logarithmic gain steps and MUTE. All gains and MUTE are independently programmable. The gain can

be set from –40.5dB to +6dB.

The stage is set to mute by default. If the microphone input is not enabled, the volume settings are set to their default

values. Changing the volume and mute control can only be done after enabling the input.

Supply & Detection

The microphone input generates a supply voltage of 1.5V above AGND. The supply is designed for

≤ 2mA and has a

10mA current limit. In OFF mode the MICS terminal is pulled to AVDD with 30k

Ω. A current of typically 50µA generates

an interrupt to inform the CPU, that a circuit is connected. When using the MICS terminal as ADC-10 input to monitor

external voltage the 30k

Ω pull-up can be disabled.

Remote Control

Fast changes of the supply current of typically 500µA are detected as a remote button press, and an interrupt is

generated.

Voice Activation

Further a built-in voice activation comparator can actuate an interrupt if microphone input voltage of about 5mVRMS is

detected.

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