Reference Design For Loudspeaker Interface; Design Considerations; Emergency Download Interface - Quectel SC606T Series Hardware Design

3.20.4. Reference Design for Loudspeaker Interface

SPK_P EARP
EA
SPK_N
RN
Module

3.20.5. Design Considerations

It is recommended to use the electret microphone with dual built-in capacitors (e.g. 10 pF and 33 pF) for
filtering out RF interference, and thereby reducing TDD noise. The 33 pF capacitor is applied for filtering
out RF interference when the module is transmitting at EGSM900. Without this capacitor, TDD noise
could be heard. The 10 pF capacitor here is used for filtering out RF interference at DCS1800. Note that
the self-resonant frequency point of a capacitor largely depends on the material and production technique.
Therefore, it is advisable to choose the most suitable capacitor for filtering out high-frequency noises after
consulting your capacitor supplier.
The severity degree of the RF interference in the voice channel during GSM transmitting largely depends
on the application design. In some cases, EGSM900 TDD noise is more severe; while in other cases,
DCS1800 TDD noise is more obvious. Therefore, a suitable capacitor should be selected based on test
results. Sometimes, even no RF filtering capacitor is required.
To decrease radio or other signal interference, RF antennas and power traces should be placed away
from audio interfaces and audio traces. Besides, power traces cannot be in parallel with the audio traces.
The differential audio traces must be kept at the same length.

3.21. Emergency Download Interface

USB_BOOT is used to force USB booting. Pulling it up to LDO5_1P8 before power-up will force the
module into download mode. This is a solution when there are failures such as an abnormal startup or
operation. For convenient firmware upgrade and debugging in the future, it is recommended to reserve
SC606T_Series_Hardware_Design
C1
33 pF
Figure 28: Reference Design for Loudspeaker Interface
SC606T Series Hardware Design
F1
F2
D1
C2
33 pF
Smart Module Series
D2
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