Specifications

TC35 / TC37 Hardware Interface Description

TC35_37_HD_02_V03.10 - Released Page 42 of 92 21.12.2001

3.6 Audio interface

Each GSM engine comprises two audio interfaces, each with an analog microphone input

and an analog earpiece output (see block diagram below).

To suit several types of equipment, there are six audio modes available which can be

selected with 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

(except for mode 1).

Please refer to Chapter 6.5 for specifications of the audio interface and an overview of the

audio parameters. Detailed instructions on using AT commands are presented in the "TC3x

AT Command Set". Table 35 summarizes the characteristics of the various audio modes and

shows what parameters are supported in each mode.

The first audio interface can be set to the audio modes 1 (default), 4 and 5. The 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 fix parameters which

cannot be modified. In audio mode 4, you can avail of AT commands to adjust the Votronic

handset as well as any individual handset.

The second audio interface is especially intended for headsets and can be configured to the

audio modes 2, 3 or 6. In order to integrate a handsfree application you can take advantage

of the Siemens Car Kit Portable and connect it to the second interface.

All microphone inputs and the earpiece / headset outputs are balanced. A power supply for

electret microphones is implemented and can be used with in audio modes 1 to 4. If not

needed, it has to be decoupled with capacitors.

Figure 15: Audio block diagram

ADC

DAC

MICP1

MICN1

MICP2

MICN2

EPP2

EPN2

EPP1

EPN1

Voiceband

Filters

RX and TX

MUX