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Hardware Development Guide of Module Product
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21
ZTE MG2618
Figure 4
–
8 SPK reference circuit
Microphone
The MIC1_N & MIC1_P are both differential interfaces, and they can also be used for single-ended
input. It’s recommended to use differential method to reduce the noises. The MIC2_P interface is used for
single-ended input. Directly connect to the microphone since these two inputs are internally provide 1.9V
bias voltage.
Speaker
The SPK1_P & SPK1_N are both differential interfaces with 32 ohm impedance, while the SPK2_P is
single-ended interface with 32 ohm impedance. There is no coupling capacitor internally, you need to add
it in the designing process.
Design of audio interface on the receiver
The output power of SPK1 is 35mW. Select the microphone with the sensitivity lower than -51.5dB
since and the max. gain inside MIC1 can reach 51.5dB. The voltage level of MIC1_P is about 1.9V.
NOTE:
If other kind of audio input method is adopted, the input signal should be within 0.5V. If the signal
voltage is lower than this value, then the pre-amplifier should be added. If the signal voltage is higher than
this value, then attenuation network should be added
Design of audio interface on the earpiece
The output power of SPK2 is 10.8 mW.Select the microphone with the sensitivity lower than -51.5dB
since and the max. gain inside MIC2 reaches 51.5dB. The voltage level of MIC2_P is about 1.9V.
Note: In order to achieve well audio
effects, it’s recommended that:
1)
During the process of using module, it’s advised to use 100pf & 33pf capacitance on its external
audio path, and serially connect with the beads to improve the audio quality.
2)
Connect TVS tube or pressure sensitive resistance on the audio path (approaching the module’s
interface) to prevent the ESD from damaging the module.
3) Make sure the use environment and module are well grounded and there is no mutual influence.
4) The power ripple supplied to the module is less than 50mV.