GSM/GPRS Modules
GSM Module Audio Design Guide
GSM Module Audo Design Guide Confidential/Release 21 / 35
2.4. Suggestion for Audio Layout
Power supply ripple, unbalanced ground and RF burst radiation have negative effect to audio layout.
Layout of MIC1P/MIC1N, SPK1P/SPK1N must meet the rule of differential signal. Moreover, these two
pairs of signals should be separated from each other by flooding ground to avoid echo issue from SPK
signal to MIC signal. Figure 18 shows an example.
Figure 18：Layout of Audio
2.5. TDD Noise Solution
It is important to avoid or reduce TDD noise in audio circuit design and layout. This chapter provides
some solution to resolve it.
1. It is strongly recommended to add an electrets-microphone within two capacitors (10pF and 33pF) in
handset and hands-free application. These two capacitors could largely suppress coupling TDD
noise from RF interference.
2. Capacitors have to place close to audio component or audio interface, layout must be short.
3. Flood ground area should be as large as possible to reduce the ground impedance and improve
ground integrality.
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