Telit Wireless Solutions GE863-QUAD, GE863-PY manual Handset Earphone Design

GE863-QUAD

GE863-PY

1vv0300715 Rev. 1 - 19/09/06

8.4 Handset Earphone Design

As seen previously, a 16Ω earpiece can be directly connected to the output pads EAR_MT+ and EAR_MT- of the GE863-QUAD / PY.

This solution is often the more cost effective, reducing the components count to a minimum. There are several limitations to the use of this solution: speaker direct connect imposes the speaker characteristics to be almost exactly the suggested ones, otherwise the power output may be reduced (if speaker impedance is bigger than 16Ω) or the GE863-QUAD / PY ear port may be damaged (if speaker impedance is less than 15Ω).

The other limitation of the speaker direct connection is the power output capability of the GE863- QUAD / PY which is limited and for some particular applications may not be enough.

For these reasons, when the power output of the GE863-QUAD / PY is not enough or if the speaker characteristics are different from the suggested, then it is preferable to use an amplifier to increase the power and current output capabilities.

Again the output from the GE863-QUAD / PY is bridged and both lines should be used, where possible, as inputs to the power amplifier. This ensures a higher common mode rejection ratio, reducing the GSM current busts noise on the speaker output.

In this case the “EAR_MT” lines from the GE863-QUAD / PY should be AC coupled with a ceramic capacitor of 100nF (or bigger ) .

It is always desirable to have a mute control on the amplifier, in order to turn it off while the device is not sending signal to the output, in this manner the amplifier background noise which may be audible during idle conditions is cut off.

A principle schematic may be:

Reproduction forbidden without Telit Communications S.p.A. written authorization - All Right reserved page 47 of 79