Only For Training And Service Purposes - LG CT815 Service Manual

3. TECHNICAL BRIEF
3.13.2 Audio signal processing & interface
3.13.2.1 MSM7201A audio interface
The MSM7201A audio front end comprises the stereo wideband codec, PCM interface, and additional
DSP audio processing.
The stereo wideband codec allows the MSM7201A 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 MSM7201A 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 sidetone 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 µF 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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