Telit GM862-QUAD/-QUAD-PY
Hardware User Guide
1vv0300692, Rev. ISSUE#0, - 04/10/2005
Reproduction forbidden without DAI Telecom written authorization – All Right reserved – Right of modification reserved
page 38 of 69
And an example of internal Ear amplifier is:
Some amplifier require a low impedance load at high frequency in order to avoid auto oscillation,
this can be made with a capacitor (100nF) in series with a resistor (15
Ω
).
When designing your application, remember to provide an adequate bypass capacitor to the
amplifier and place it close to the power input pin of the IC, keeping the traces as short as possible.
6.4 Hands Free earphone (low power) design
The same design considerations made for the handset are valid for the hands free earphone, the only
difference is that the external ear audio output level from the GM862-QUAD is 6dB lower than the
internal one, so the gain of the amplifier must be 6dB higher to provide the same audio level.
6.5 Car Kit speakerphone design
For the car kit speaker phone function the power output requirement is usually at least 4W,
therefore an amplifier is needed to boost the GM862-QUAD output.
The design of the amplifier shall comply with the following guidelines:
•
The input to the amplifier MUST be taken from the external audio path (, EAR_HF-)
of the GM862-QUAD, because of its echo canceller parameters suited to a car cabin use.
•
The amplifier shall have a gain of 30-40 times ( 29-32 dB) to provide the desired output power
of 5-10W with the signal from the GM862-QUAD external audio output lines (EAR_HF).
•
If the amplifier has a fixed gain then it can be adjusted to the desired value by reducing the input
signal with a resistor divider network.
