Neo_M680 GPRS Module Hardware User Guide
Copyright © Neoway Technology Co., Ltd
24
Figure 3-22
Reference design of MIC differential connections
In Figure 3-23, a bias voltage for microphone is provided through MICP and MICN. But if an amplifier is
used between the microphone and module, capacitors like C1 and C2, should be placed between the outputs
of amplifier and module, to block the bias voltage.
For a peak voltage greater than 200 mV AC, an attenuation circuit comprised of R1-R4 should be used.
Figure 3-23
Reference design for common audio input
In above figures, the audio input circuits are designed to meet the requirements for small audio signal, far
away from interference source and masking PCB routing by ground.
Figure 3-24 shows a reference design for the receiver interface, through which a 32 Ω receiver can be driven
directly.
GPRS Module
33 pF
MIC
33 pF
100 pF
MICN
MICP
GPRS Module
33 pF
33 pF
MICN
MICP
MIC_BIAS
Baseband
Circuit
2.2 uF
2.2K
C1
C2
User's
Circuit
R1
R3
R2
R4
·
2.2K
R6
R5
