The AD1886A contains an internal microphone preamp with 20 dB gain; in most cases a direct microphone connection as shown inFigure 16 is adequate. If the microphone level is too low, an external preamp can be added as shown in Figure 17. In either case themicrophone bias can be derived from the codec’s internal reference (VREFOUT) using a 2.2 kΩ resistor. For the preamp circuit, theVREFOUT signal can also provide the midpoint bias for the amplifier.
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