CLM920_NC3_LTE Module Hardware User Guide
Shang Hai YUGE Information Technology co., LTD
Page 26 of 37
3.11.1 Analog Voice Reference Design
Figure 3-22 Analog voice reference circuit
The MIC+/MIC-channel is used as a differential input for the microphone. The internal bias voltage
required for the microphone operation is provided inside the module. No external bias circuit is
required. The microphone usually uses an electret microphone.
The SPK+/SPK-channel is usually used for the handle, earphone or external power amplifier. If the
customer needs an external audio amplifier, it will switch to the headphone channel output signal
through AT+CSDVC=4, and then the external audio amplifier will amplify the signal.
The audio signal is sensitive and should be placed away from the radiation source and power
interface. The traces should be as short as possible and protect sensitive signals.
To prevent TDD noise, the filter capacitors are reserved for 10pF and 33pF when designing the audio
circuit to remove the RF interference signal.
The customer can set the handle output by using the AT+CSDVC=4 command, the AT+CSDVC=2