The H603 module processes digital voice signals for the DSP, the input voice signal “AUDIO_IN” goes into
the audio frequency amplifier AW8736, achieving the amplification and power drive of analogue voice
signals.
3.4.3 SIM Card Interface Circuit
A SIM card supports power supply of 1.8V and 3V, and SIM card data is read through the H603 module.
The circuit is composed of the card clock signal SCLK, the card reset signal SRST, the card data signal
SIO and the power supply detection signal PMU. The frequency band of a SIM card is about 3.25MHz, so
the SIM socket is near the interface of the SIM module, to avoid influence on communication signals due
to wave distortion caused by an overlong wire. A capacitor of 33PF is added onto the signal lines SCLK,
SRST and SIO to filter the interference of antenna signals. For these four signals, static is avoided using a
TVS (transient voltage suppressor) or ESD (electrostatic discharge) component.
3.4.4 MIC Circuit
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