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GE864 Hardware User Guide
1vv0300694 Rev.10 - 10/06/08
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 42 of 69
9.2 OUTPUT LINES (Speaker)
9.2.1 Short description
The Telit GE864-QUAD / PY 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:
Æ
the “EAR_MT” lines EPN1 and EPP1 are the Differential Line-Out Drivers ; they can drive an
external amplifier or directly a 16 Ω earpiece at –12dBFS (*) ;
Æ the “EAR_HF” lines EPPA1_2 and EPPA2 are the Fully Differential Power Buffers ; they can
directly drive a 16Ω 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 should be used for handset function, while the “EAR_HF” audio path is
suited for hands-free function (car kit).
Both receiver outputs are B.T.L. type (Bridged Tie Load) and the OEM circuitry shall be designed
bridged to reduce the common mode noise typically generated on the ground plane and to get the
maximum power output from the device; however also a single ended circuitry can be designed for
particular OEM application needs.