AS3517 datasheet(19/94 Pages) AMSCO

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AS3517 V17

Data Sheet, Confidential

www.austriamicrosystems.com

9.1.2

Microphone Inputs (2x)

General

The AFE offers two microphone inputs and 2 low noise microphone voltage supply (microphone bias), voice activation, microphone

connect detection and push button remote control.

Figure 6 Microphone Input

Microphone Preamplifier and Gain Stage

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. electrete

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

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

≤2mA and has a 10mA current

limit. In OFF mode the MICS terminal is pulled to AVDD with 30kOhm. A current of typically 50uA generates an interrupt to inform the

CPU, that a circuit is connected. When using HPCM as headset ground the HP–stage gives the interrupt. After enabling the HP-stage

through the CPU the microphone detection interrupt will follow.

When using the MICxS terminals as ADC-10 input to monitor external voltages the 30kOhm pull-up can be disabled.

Remote Control

Fast changes of the supply current of typically 500uA are detected as a remote button press, and an interrupt is generated. Then the CPU

can start the measurement of the microphone supply current with the internal 10-bit ADC to distinguish which button was pressed. As the

current measurement is done via an internal resistor, only two buttons generating a current of about 0.5mA and 1mA can be detected.

With this 1mA as microphone bias is still available.

Voice Activation

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

Revision 1v3

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