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FIBOCOM MC610 Series Hardware Guide
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heard during a call. It should be noted that since the capacitor resonance point largely depends on the
capacitor material and manufacturing process, when choosing a capacitor, it is recommended to consult
the capacitor supplier and choose the most suitable capacitance to filter out the high-frequency noise
when working in EGSM900/DCS1800.
The severity of high frequency interference during GSM transmission usually depends on the customer's
application design. In some cases, the TDD noise of EGSM900 is more serious, and in some cases, the
TDD noise of DCS1800 is more serious. Therefore, customers can choose the required filter capacitor
according to the test results (MC615 module has no GSM).
The RF filter capacitor on the PCB board should be placed as close as possible to the audio device or
audio interface, and the route should be as short as possible, and must be passed through the filter
capacitor to other connection points. The antenna position should be as far away as possible from audio
components and audio routes to reduce radiation interference. The power lines and audio lines should
not be parallel, and the power lines should be as far away as possible from the audio lines. Differential
audio routes must follow the wiring rules for differential signals.
3.10.3 Handset Interface Circuit
Figure 3-17 Reference circuit of SPK output
