User manual

MTX-HSPA-PH8-P+G UMTS-HSPA terminal modem http://www.matrix.es
MTX-HSPA-PH8-P+G User Manual V.1.0 Pag. 16
Preliminary. Subject to change without prior notice
3.2 Audio Connector
A 6-way 4-poles RJ connector, as shown below, allows a telephone handset to be plugged into the
modem, giving access to the microphone and earpiece signals. The connector may also be used to drive
other analogue audio sub-systems or devices.
The audio interface provides one analog input for a microphone and one analog output for an earpiece.
• The microphone input and the earpiece output are balanced.
• For electret microphones, a supply source is implemented.
• The MTX-HSPA-PH8-P+G is pre-configured to work with a range of handsets. The audio interface is
flexible and its performance can be configured using AT commands to match a particular handset or audio
subsystem.
Audio handset connection.
A power supply for electret microphones is already fed to MICP connection. Microphone signals are fed via
the MICP and MICN pins to an analog-to-digital converter (ADC) and the DSP. The DSP application core
calculates e.g. digital gains, sidetone, echo cancellation or noise suppression depending on the current
configuration of the audio path. The processed speech samples are passed to the speech encoder.
Received samples from the speech decoder are passed to the digital-to-analog converter (DAC) after post
processing (frequency response correction, adding sidetone etc.). The loudspeaker signal is routed via EPP
and EPN pins.
The audio parameters are set with the AT commands AT^SNFI as well as AT^SNFO and are stored on the
volatile memory for the current audio mode.
In order to support different types of equipment, the audio interface can be configured with different
audio modes via the AT^SNFS command. The electrical characteristics of the voiceband part vary with the
audio mode. For example, sending and receiving amplification, sidetone paths, noise suppression etc.
depend on the selected mode and can be set with AT commands.
The default audio mode (AT^SNFS=1) is intended to be used with the audio interface. This default
configuration is optimized for the Votronic HH-SI-30.3/V1.1/0 handset and used for type approving the
Siemens reference configuration. Audio mode 1 has fixed parameters that cannot be modified.
Pin Signal Dir Description
0 Not connected
1 MICN I Microphone
negative input
2 EPN O Earpiece negative
output
3 EPP O Earpiece positive
output
4 MICP I Microphone positive
input
5 Not connected