Siemens TC35i - Manual (Page 23)

TC35i Terminal Hardware Interface Description
Confidential / Released
TC35i_T_HD_v01.05 Page 23/37 10.07.2003
The audio interface can be configured by AT commands. Please note that the 2 nd audio
interface mentioned in [1] is not connected. Audio modes 2, 3 and 6 can be selected by
setting AT^SAIC=2,1,1, for further details refer to [1].
The electrical characteristics of the voiceband part vary with the audio mode. To suit several
types of audio equipment, three audio modes given by default can be selected by the AT
command AT^SNFS, see [1]. In audio mode 4 and 5, the gain in the microphone, earpiece
and the sidetone path can be adjusted from the cellular device application (different volume
steps can be selected by AT commands). See Table 15: AT adjustable parameters for the
characteristics of the audio modes.
Table 6: Audio modes
Mode No
AT^SNFS= 1 4 5
Name Default Handset User Handset Plain Codec 1
Purpose Recommended
handset (see
chapter 6) User provided
handset Direct access to
speech coder
Gains programmable via AT
command NO YES YES
Sidetone YES YES YES
Volume control NO YES YES
Limiter (receive) YES YES NO
Echo control (send) Suppression Suppression NO
Noise suppression NO NO NO
MIC input signal for 0dBm0
@ 1024 Hz
(at default gain settings) 12.5 mV 12.5 mV 315 mV
Earpiece output signal in mV eff.
@ 0dBm0, 1024 Hz, no load (at
default gain settings);
@ 3.14 dBm0
275 mV 275 mV
default @ max
volume 880 mV
3.7 Vpp
Sidetone gain (at default settings) 27.7 dB 27.7 dB -∞ dB
Speech processing:
The voiceband filter includes a digital interpolation low-pass filter for received voiceband
signals with digital noise shaping and a digital decimation low-pass filter for voiceband
signals to be transmitted.
After voiceband (interpolation) filtering the resulting 2Mbit/s data stream is digital-to-analog
converted and amplified by a programmable gain stage in the voiceband processing part.
The output signal can directly be connected to the earpiece of the GSM cellular device or to
an external handset earpiece (via I/O connector). In the opposite direction the input signal
from the microphone is first amplified by a programmable amplifier. After analog-to-digital
conversion a 2Mbit/s data stream is generated and voiceband (decimation) filtering is
performed.
The resulting speech samples from the voiceband filters are handled by the DSP of the