User Manual

Bluetooth Audio Module
Ehong Technology Co., Ltd
6.10. Microphone input
The module contains 2 independent low-noise microphone bias generators. The
microphone bias generators are recommended for biasing electret condensor
microphones. Figure 9.6 shows a biasing circuit for microphones with a sensitivity
between about ‑ 40 to ‑ 60dB (0dB = 1V/Pa):
Where:
■
The microphone bias generators derives their power from VBAT or VOUT_3V3 \
and requires no capacitor on its output.
■
The microphone bias generators maintains regulation within the limits 70μA to
2.8mA, supporting a 2mA source typically required by 2 electret condensor
microphones. If the microphone sits below these limits, then the microphone
output must be pre-loaded with a large value resistor to ground.
■
Biasing resistors R1 and R2 equal 2.2kΩ.
■
The input impedance at MIC_LN, MIC_LP, MIC_RN and MIC_RP is typically 6kΩ.
■
C1, C2, C3 and C4 are 100/150nF if bass roll-off is required to limit wind noise on the
microphone.
■
R1 and R2 set the microphone load impedance and are normally around 2.2kΩ.
Figure 13: Microphone Biasing (Single Channel Shown)