LG -A230 Service Manual page 53

3. TECHNICAL BRIEF
Figure 3.12.4 Different Application Scenarios
In order to achieve the single-speaker concept by parallel connection of Earpiece and Headset amplifier the
Earpiece amplifier have to sustain the up to 5 V voltage of the class-D amplifier.
Audio-in Path
The audio-in path of X-GOLD™215 provides two differential microphone input sources, MIC1and MIC2.
• The inputs for microphone MIC1 are MICP1 and MICN1.
• The inputs for microphone MIC2 are MICP2 and MICN2.
The audio-in path consists of an input selector, a low noise amplifier and following pre-filter with gain control,
a second order -converter and a digital decimation filter. It supports both standard GSM (bandwidth 3.5
kHz) and wideband (bandwidth 7 kHz) speech bands.
The differential input signal from the microphone first passes a low noise amplifier and following pre-filter
and an anti-aliasing pre-filtering stage achieving and overall variable gain ranging from 0 dB to +39 dB . The
signal is then modulated by a second order -converter which is clocked with the same clock rate as the
digital to analog converters. The -converter delivers a 1-bit pulse density modulated data stream at a rate
of 2 MHz to the digital decimation filter which reduces the rate to 8 kHz or 16 kHz, depending on the current
mode.
To improve SNR the sample frequency can be doubled in dedicated modes and the modulated data stream is
4MHz instead of 2 MHz.
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