question on input power in PA

[hermit2003]

in cdma pa design, the input power is not constant when the output power is fixed (e.g. 28dBm). the input power generally vary from several -dBm to several +dBm.

so the question is how to make a stable output power when the input power is varied. anybody know some solutions?
thanks a million.

 

[dunn]

Have a look for the data sheets for: MAX2264, MAX2265, MAX2266

 

[vfone]

The CDMA PA for a mobile phone has the Input Power variable, and the Output Power variable also (from –50dBm up to +28dBm). The Gain of the PA is constant.
A constant output power when the input is variable you can obtain when the PA have variable gain.

 

[hermit2003]

so how can i get a variable gain in PA, couple a power detector at the output port of the power stage of PA and feed back to the input port of the drive stage of PA, and when the output power is more or less than 28dBm, then make the input power decrease or increase ?!

 

[vfone]

In CDMA the power control is done by an Open Loop and by a Closed Loop.
In Closed Loop the process involves both, the Base Station and the mobile.
The Base Station continuously monitors the reverse link and command the mobile to change the power up and down, very fast (1500 times/second).
Inside the mobile the gain of the PA is constant, so the power control is done at the input of the PA by the VGA (Variable Gain Amplifier).
If the Gain of the PA is not changing with Temperature and Vcc, the output power at antenna connector will follow the calibrated values.

 

[springf2000]

use the ALC circuit is the simplest way to to this job!
this is a common way to stabilize the output power of the PA