User's Manual

PCS3_HD_v01.000-03
Confidential / Preliminary
Page 42 of 101
2013-10-21
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PCS3 Hardware Interface Description
3.8 Analog Audio Interface
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MICP leads the signal via to the non-inverting input of the operational amplifier which is then
connected via to AGND. The gain of
the input stage can be programmed by the parameter
<micAmp1>, A gain stage follows that can be set to 0dB or 24dB using <micAmp1>. If 24dB is
spec-
ified, the common mode rejection ratio is reduced accordingly.
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Finally, the uplink gain can be scaled in the PCM path by the <micTxVol> parameter.
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It is recommended to use the AGND line for grounding the microphone circuit. AGND provides
for the same module ground potential the analog circuits of the module refer to. AGND must
not be connected to the system GND anywhere. Otherwise high burst peak currents may flow
across AGND causing humming in the uplink audio signal.
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A regulated power supply for electret microphones is available at VMIC. The voltage at VMIC
is rated at 1.8V at 3mA and is available while audio is active (e.g., during a call).