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Captured to AIC23 - Characteristics of the Microphone Input wiki page

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FAQ: What are the characteristics of the Microphone Input?

Mike Caruso
Prodigy 155 points

Answer:
If the microphone does not require a bias of greater than 3ma and the gain of the microphone input is sufficient then the AIC23 should work just fine. I will summarize the MIC Power tolerance to the AIC23 to give you more to work with. The ADC Full Scale input is 1.0V RMS at AVDD=3.3 Volts. Any voltage greater than full scale will possibly overload the ADC and cause distortion. Note that the full scale input tracks directly with AVDD. The Microphone gain can range from -6dB to 34dB. An external MIC resister of 90K Ohms will give a gain of 0.5 (-6dB). An external MIC resister of 0 Ohms will give a gain of 5 (14dB) and the 20dB gain will yield a 34dB gain to the ADC. If you input 200MvRMS with 0 dB boost and no external resister then the voltage to the ADC will be 200mv * 5 = 1vRMS and this should not saturate the ADC. If you used a 20dB boost then the voltage to the ADC would exceed 1volt and it would cause some distortion. This is the same case as the Line Inputs.