Motorola Mobility LLC T56KT1 User Manual
Chapter 2: Hardware Interface Description
December 15, 2009
G30 - Module Hardware Description
39
Gain Control
The amplification (gain) level for each input and output device can be configured through AT
commands. Both basic and advanced audio modes provide AT commands to set the desired gain
levels for each audio path and audio sound type.
commands. Both basic and advanced audio modes provide AT commands to set the desired gain
levels for each audio path and audio sound type.
gives the gain control features.
Audio Design
The audio quality delivered by G30 is highly affected by the application audio design,
particularly when using the analog audio interface. Therefore, special care must be taken when
designing the G30 audio interface. Improper design and implementation of the audio interface
will result in poor audio quality.
particularly when using the analog audio interface. Therefore, special care must be taken when
designing the G30 audio interface. Improper design and implementation of the audio interface
will result in poor audio quality.
Poor audio quality is a result of electrical interferences, or noises, from circuits surrounding the
audio interface. There are several possible sources for the audio noise:
audio interface. There are several possible sources for the audio noise:
•
Transients and losses on the power supply
•
EMI from antenna radiations
•
Digital logic switching noise
Most of the audio noise originates from the GSM transmit burst current surges (217 Hz TDMA
buzz), which appear on the main power supply lines and antenna, but also indirectly penetrate the
internal application's supplies and signals. The noises are transferred into the G30's audio circuits
through the microphone input signals and then are amplified by the G30's internal audio
amplifiers.
buzz), which appear on the main power supply lines and antenna, but also indirectly penetrate the
internal application's supplies and signals. The noises are transferred into the G30's audio circuits
through the microphone input signals and then are amplified by the G30's internal audio
amplifiers.
To minimize the audio noise and improve the audio performance the microphone and speaker
signals must be designed with sufficient protection from surrounding noises.
signals must be designed with sufficient protection from surrounding noises.
The following guidelines should be followed to achieve best audio performance:
•
Reference the microphone input circuits to the G30 AGND interface signal.
•
If using single-ended audio outputs, they should be referenced to the G30 AGND interface
signal.
signal.
•
Keep the audio circuits away from the antenna.
•
.
•
The audio signals should not be routed adjacent to digital signals.
Table 2-16: Gain Control Features
Device
Gain Command
Default
Gain
Description
Basic
Advanced
Microphone
AT+MMICG
AT+MMICG
8
Sets input speech gain level.
Headset Micro-
phone
phone
8
Sets input speech gain level.
Mono Speaker
AT+CLVL
AT+MAVOL
4
Sets voice and DTMF gain.
Differential Speaker AT+CRSL
4
Sets rings and alerts gain.