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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

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

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Siemens TC35i Manuel d'utilisateur Page 23

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