A simple question about PA selection.

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tsunghan

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Hi !
I am just a beginner and want to design PA used in 802.11b/g. What's the key point i must pay attention to during selection ? Bluetooth is also working at 2.4GHz ISM band. Can I use the PA which is designed for Bluetooth such as RFMD RF2172 in my design ? What will happen if I do this ? Similarly, what will happen if I use a PA designed for WLAN on Bluetooth module ? Is it possible to use a PA at 2.4GHz with both WLAN and Bluetooth on board simultaneously ? Could anyone give me an advise about it. Thanks in advance.
 

HI,
Does the PA mean the phased array?If it is,thanks for help!
 

The criteria for selection of an PA..
Most important descending
-Class
-P1dB Compression Level or Maximum Output Power
-IP3 and IP5 ( e.g. Harmonic Levels )
-Power Gain
-Cost
-Power Consumption and PAE ( and related with Power Added Efficieny)
-Input and Output Impedances ( e.g. S11 and S22 )
-Placement Room and heatsinking properties
-Reliability
-Maximum permitted Input Power
-Feasibility..

Bluetooth uses GFSK Modulation. In fact Class C may be sufficient depending on Harmonic levels and other spectral regrowth specifications.

But Generally Clas AB is used for this purpose.
 

PA for WLAN need a lot of power backoff.
Because the modulation type is QPSK for 11b and 64QAM for 11g at maximum data transfer rate. In these modulation, the linearity of front-end circuit is more important. Therefore, the backoff is needed. So it would cost much current consumption in this application.
As for Bluetooth, the GFSK modulation care less linearity. Class AB or C can be used. The efficiency is much better in Bluetooth application.
 

So, if I don't care about current consumption in this design. The Power Amplifier designed for WLAN can be used in Bluetooth application. But the PA designed for Bluetooth can't be used in WLAN application because of less linearity. Is it correct ?
 

Hi , what is deffrent between the voltage control and current control for PA ?
 

Sure! But in personal communication system or portable device which concerned about battery lifetime will take much attention in power saving.
 

hi

I think the best solution for power saving, using "Zig-bee" {IEEE 802.15.4} protocol...mainly for ultra low power transceiver. But for WLAN, Wi-Fi is the dominant way for communication. as you don't care about the power budget.
 

In WLAN PA evaluation one of the most important parameter after P1dB is EVM.
This parameter is critical in a WLAN communication system.
You can find PA’s with identical P1dB, but with different EVM at the same output power.
regards
 

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