User guide

UC864-E/G/WD/WDU Hardware User Guide

1vv0300766a Rev.4

- 03/02/09

“Mic_HF” 2nd differential microphone path

• line coupling AC*

• line type balanced

• coupling capacitor ≥ 100nF

• differential input resistance 20kΩ

• differential input voltage ≤ 65mVpp (23mVrms)

• microphone nominal sensitivity -45 dBVrms/Pa

• analog gain suggested +10dB

• echo canceller type car kit hands-free

10.2. OUTPUT LINES (Speaker)

10.2.1. Short Description

The Telit UC864-E/G/WD/WDU provides two audio paths in receive section. Only

one of the two paths can be active at a time, selectable by AXE hardware line or by

AT command.

You must keep in mind the different audio characteristics of the receive blocks when

designing:

• the “Ear_MT” lines EPN1 and EPP1 are the Differential Line-Out Drivers ;

they can drive an external amplifier or directly a 32 Ω earpiece at –

12dBFS (*) ;

• the “Ear_HF” lines EPPA1_2 and EPPA2 are the Fully Differential Power

Buffers ; they can directly drive a 32Ω speaker in differential (balanced) or

single ended (unbalanced) operation mode.

(*) FS: acronym of Full Scale. It is equal to 0dB, the maximum Hardware Analog

Receive Gain of BaseBand Chip.

The “Ear_MT” audio path must be used for handset function, while the “Ear_HF”

audio path is suited for hands-free function (car kit).

(*) WARNING:

AC means that the signals from microphone have to be connected to the input lines

of the module by a CAPACITOR, the value of which must be ≥ 100nF. By not

respecting this constraint, the input stage will be damaged.