User's Manual

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Figure 16: Example circuit for SPDIF interface (Optical)
7.2.4 Microphone Input
The audio-input is intended for use from 1μA@94dB SPL to about 10μA@94dB SPL. With biasing
resistors R1 and R2 equal to 1kΩ, this requires microphones with sensitivity between about –40dBV and
–60dBV.
The MIC_BIAS is like any voltage regulator and requires a minimum load to maintain regulation. The
MIC_BIAS will maintain regulation within the limits 0.2 - 1.53 mA depending on the bias current setting.
This means that if a microphone that sits below these limits is used, the microphone output must be pre-
loaded with a large value resistor to ground.
MIC_BIAS line either be used as an enable signal for an external biasing regulator. The default setting
for the bias current in WT32 is 0.2 mA and it is recommended to use an external low noise biasing
regulator for the best noise performance. The recommended microphone biasing circuitry is shown in
the Figure 17.
C3
C4
MIC_BIAS
MIC
AUDIO_IN_P_LEFT
AUDIO_IN_N_LEFT
R1
R2
C1
C2
2V7
regulator
EN
OUT
IN VDD_BAT
Figure 17: Recommended microphone biasing (left channel shown)