Smart LTE Module Series
SC66 Hardware Design
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3.22.3. Reference Circuit Design for Headphone Interface
20K
MIC_GND
MIC2_P
HPH_L
HS_DET
HPH_R
HPH_REF
33pF
Module
R1
0R
6
3
4
5
2
1
33pF 33pF
C3
C4
C5
F3
F2
F1
D1 D2 D3 D4
F4
R2
R3
0R
D0
Figure 33: Reference Circuit Design for Headphone Interface
3.22.4. Reference Circuit Design for Loudspeaker Interface
EARP
EA
RN
F2
SPK_P
SPK_M
33pF
33pF
C1
C2
F1
Module
D1
D2
Figure 34: Reference Circuit Design for Loudspeaker Interface
3.22.5. Audio Interfaces Design Considerations
It is recommended to use the electret microphone with dual built-in capacitors (e.g. 10pF and 33pF) for
filtering out RF interference, thus reducing TDD noise. The 33pF capacitor is applied for filtering out RF
interference when the module is transmitting at EGSM900. Without placing this capacitor, TDD noise
could be heard. The 10pF capacitor here is used for filtering out RF interference at DCS1800. Please note
that the resonant frequency point of a capacitor largely depends on the material and production technique.
Therefore, customers would have to discuss with their capacitor vendors to choose the most suitable
