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Only for training and service purposes
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3. TECHNICAL BRIEF
The MSM7227 audio front end comprises the stereo wideband codec, PCM interface,
and additional DSP audio processing.
The stereo wideband codec allows the MSM7227 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 MSM7227 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
Ɇ
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.
3. Technical Brief
3.7.2 Audio signal processing & interface
3.7.2.1 MSM7227 audio interface