Telit GE863-QUAD / GE863-PY
Hardware User guide
1vv0300697, Rev. ISSUE#0, - 21/11/05
Reproduction forbidden without Telit Communication written authorization – All Right reserved – Right of modification reserved
page 39 of 69
high power external ear
• line coupling:
DC
• line type:
bridged not referred to GND
• speaker impedance (operating conditions):
≥ 4 Ω
• minimum load impedance:
4 Ω
• signal bandwidth:
150 - 8000 Hz @ -3 dB
• maximum power output:
6 W
• THD+N
10% @ 6 W
7.2 General Design rules
There are several configurations for the audio output path, but the various design requirements
can be grouped into three different categories:
• handset earphone (low power, typically a handset)
• hands free earphone (low power, typically a headset)
• car kit speakerphone (high power, typically a speaker)
The three groups have different power requirements, usually the first two applications need only
few mW of power, which can be directly drained from the GE863-QUAD pads, provided a
suited speaker is used. This direct connect design is the cheaper and simpler solution and will be
suited for the most of the earphone design requirements. There's no need to decouple the output
ear lines if a suited earpiece is connected. For the last group, the speakerphone, a power
amplifier is required to raise the output power up to 5-10W required in a car cabin application.
All the designs shall comply with the following guidelines:
• Where possible use a bridged earphone circuitry, to achieve the maximum power output
from the device.
• Keep the earphone traces on the PCB and wires as short as possible.
• If your application requires a single ended earpiece and you want a direct connection, then
leave one of the two output lines open and use only the other referred to ground. Remember
that in this case the power output is 4 times lower than the bridged circuit and may not be
enough to ensure a good voice volume.
• Make sure that the earphone traces in the PCB don't cross or run parallel to noisy traces
(especially the power line)
• The cable to the speaker shall be a twisted pair with both the lines floating for the bridged
output type, shielded with the shield to ground for the single ended output type.
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