Figure 26: Reference Circuit Design for Headphone Interface
3.22.4. Reference Circuit Design for Loudspeaker Interface
Figure 27: Reference Circuit Design for Loudspeaker Interface
3.22.5. Design Considerations for Audio Interfaces
It is recommended to use the electret microphone with dual built-in capacitors (e.g. 10 pF and 33 pF) to
filter out RF interference, thus reducing TDD noise. The 33 pF capacitor is applied to filter out RF
interference when the module is transmitting at EGSM900. Without this capacitor, TDD noise could be
heard during voice calls. The 10 pF capacitor is used to filter out RF interference at DCS1800. Please
note that the resonant frequency point of a capacitor largely depends on its material and manufacturing
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