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3. TECHNICAL BRIEF
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Figure 3.12.4 Different Application Scenarios
3. TECHNICAL BRIEF
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™213 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 ȭȟ-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 ȭȟ-converter which is clocked with the same clock rate as
the digital to analog converters. The ȭȟ-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.