Telit Wireless Solutions UC864 manual Audio Section Overview, Generality, Definitions, Selection

UC864-E Hardware User Guide

1vv0300766a Rev.1 - 31/01/08

10 Audio Section Overview

10.1 Generality

The UC864-EAudio Section provides two audio paths both in transmit and in receive sections, active only one at time. Two buffering amplifiers could be used in Differential or Single Ended configuration. To select the well-suited section, refer to paragraph 10.3 Selection mode.

For applications and suggestion refer to the Telit modules Audio Application Note (80000NT10007a)

10.2 Definitions

The Baseband chip was developed for the cellular phones, which needed a couple of amplifiers to be used with internal audio transducers and another couple to be used with external ones , both in transmit and in receive sections . Two different definitions were introduced to distinguish the schematic signals and the Software identifiers, with the following meaning:

•HS or MT Æ internal audio transducers (from HandSet or MicroTelephone )

•HF Æ external audio transducers (from HandsFree )

We have not changed the HS and HF acronyms with UC864-E, keeping them both in the Software and on the schematics. But we want you to remember that if you don’t have any load driving constraint (like a speaker with an impedance coil lower than 16Ω) this distinction is not relevant, because the two sections:

•have fully equivalent electrical performances (like the two microphone amplifiers)

•activate the same functionalities (like the Echo Canceller module)

•offer slightly different performances (like the two speaker buffering stages)

Being the performances of the two blocks like the same in this case, the choice could be done as example in order to overcome the PCB design difficulties, respecting the electrical characteristics.

10.3 Selection

The activation of the requested audio section is made Hardware by AXE line or Software by AT#CAP command, turning on:

•an output stage to drive a low resistive load earpiece and an input stage to drive the local microphone when AUDIO-1 mode (HS/MT) ;

•an output stage to drive a high resistive load headset and an input stage to drive the headset microphone when AUDIO-2 mode (HF) .

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