LG E900 Service Manual page 50

3.11.2 Audio signal processing & interface
QSD8650 audio interface
The QSD8650 audio front end comprises the stereo wideband codec, PCM interface, and additional DSP
audio processing.
The stereo wideband codec allows the QSD8650 device to support stereo music/ringer melody
applications in addition to the 8 kHz voice band applications on the forward link.
In the audio transmit path, the device operates as 13-bit linear converter with software, selectable 8 kHz
and 16 kHz sampling rate. In the audio receive path, the device operates as a software-selectable 13-bit or
16-bit linear converter with software selectable 8 kHz, 16 kHz, 22.05 kHz, 24 kHz, 32 kHz, 44.1 kHz, or 48
kHz sampling rate. Through software, the Rx path can be configured as either a mono or stereo output.
New to the QSD8650 device is a transmit (Tx) ADC path that now supports stereo wideband sampling.
The integrated codec contains all of the required conversion and amplification stages for the audio front
end. The codec operates as a 13-bit linear codec with the transmit (Tx) and receive (Rx) filters designed to
meet ITU-T G.712 requirements. The codec includes a programmable side tone path for summing a
portion of the Tx audio into the Rx path.
An on-chip voltage/current reference is provided to generate the precise voltages and currents required
by the codec. This circuit requires a single capacitor of 0.1 F to be connected between the CCOMP and
GND pins. The on-chip voltage reference also provides a microphone bias voltage required for electret
condenser microphones typically used in handset applications. The MICBIAS output pin is designed to
provide 1.8 V DC while delivering as much as 1 mA of current. Audio decoder summing and headset
switch detection are included.
The codec interface includes the amplification stages for both the microphone and earphone. On the
transmit (Tx) path, the interface supports two differential microphone inputs, a differential auxiliary input,
and a stereo line input. On the receive (Rx) path the interface supports one differential earphone output, a
stereo single-ended headphone output, one differential auxiliary output, and stereo single-ended line
outputs.
The codec is configured by the codec SBI registers. The codec interface is shown in Figure.
Also part of the audio front end is the PCM interface. The PCM interface allows for an external codec to be
used instead of the internal codec. This interface can be used in I2S mode which will allows for an external
stereo DAC to be used.
Finally, the audio front end includes additional DSP audio processing that does gains, filtering and other
audio processing.
The DSP audio processing is configured through the QDSP5000 command types and is not directly
controlled by the microprocessor.
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Only for training and service purposes
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3. TECHNICAL BRIEF
LGE Internal Use Only