Telit Wireless Solutions GE863-QUAD Manual Do Utilizador

 
 
 
 

 

 

 1vv0300715 Rev. 1 - 19/09/06  

  

Reproduction forbidden without Telit Communications S.p.A. written authorization - All Right reserved 

 

page 49 of 79 

 

8.6  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 GE863-QUAD / PY output. 
The design of the amplifier shall comply with the following guidelines: 
 
•  The input to the amplifier MUST be taken from the “Ear_HF” audio path of the GE863-QUAD / PY, 

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 GE863-QUAD / PY “Ear_HF” audio output lines. 

•  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. 

•  The amplifier shall have a mute control to be used while not in conversation. This results in two 

benefits: eliminating the background noise when not in conversation and saving power. 

•  The power to the amplifier should be decoupled as much as possible from the GE863-QUAD / PY 

power supply, by either keeping separate wires and placing bypass capacitors of adequate value 
close to the amplifier power input pads. 

•  The biasing voltage of the amplifier shall be stabilized with a low ESR (e.g. a tantalum) capacitor of 

adequate value.  

 

 
 Example of car kit amplifier schematic.