Specifications

43
Figure 16: Example circuit for SPDIF interface (Co-Axial)
Figure 17: 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 bee used to directly drive bias current for the microphone, or 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 18.