Nokia c2-00 Service Manual page 149

RM-704
System Module
The internal microphone inputs via filtering components to the MICP1 and MICN1 inputs of XGold213. DC
blocking capacitors C2102 are inserted to center the audio input around the internal bias level. The
microphone circuit is configured in pseudo-differential mode. VMIC is used for the bias. A low-pass filter
comprising R2100 and C2101 is used to remove any potential noise picked-up by VMIC. The external
microphone for the headset is connected via filtering components to the second differential microphone
input MICP2 and MICN2, and is designed pseudo-differentially for better noise immunity. DC blocking
capacitors C2107 are used for the biasing. A low-pass filter comprising R2105 and C2105 removes any
potential noise picked-up by VUMIC. As a relatively high gain is applied to the uplink signal in the X-GOLD213,
a noise suppression filter is inserted. Microphone signals are connected differentially between X-GOLD213
and filter circuitry in order to achieve a good common mode noise rejection.
Downlink audio can be routed to the headset output drivers, earpiece driver or the class-D speaker amplifier.
Figure 57 X-Gold213 audio output selection
The X-Gold213 features stereo headset drivers, each driving a 16ohm load with an output power up to
30mWrms. With different register settings, either a stereo or mono configuration can be selected. In the
mono configuration, only the R-DAC is used, with the signals still routed through to both HSR and HSL. The
X-Gold213 also contains a charge pump which is used to supply the internal headset amplifier in bipolar
mode (generates -1.3V). When using this mode, the external DC blocking capacitor can be removed. For
Quantum only bipolar mode will be supported. For this application an external capacitor C3016 is connected
to the CP1 / CP2 balls. The charge pump is driven by a 13 MHz clock.
The EP buffer (EPP and EPN) is specified to have a max power output of 100mWrms, at a load16ohms.
Figure 58 Dual and single speaker configurations
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