What type of impedance matching is suitable for class A PA ?

[selvaraja]

impedance matching

Hi

What type of impedance matching suitable for PA if you developing it for class A PA (power Amplifier) for IEEE 802.11a standard where you have to deliver 70 mW to load ( antenna 50 ohm)

regards

 

[vfone]

Re: impedance matching

Usually, LPF matching topology is used for this kind of application.

 

[DJ]

Re: impedance matching

If I understand you correctly the load should be as Zopt, the load for max power. It can be found using a load pull test. Usually the load is LC,(LPF as mentioned).

 

[selvaraja]

Re: impedance matching

Hi

Thk you for valuable input but for my case the supply is 3.3 v and maximum power should deliver to antenna is 17 dBm , the frequency of interest is 5 Ghz How do i calculate the L & C value for this kind of configuration. Thk you in advance.

regards,

selvaraja

 

[DJ]

Re: impedance matching

If you have a nonlinear model for the device you can find Zopt first and then match from load (50 ohm) to Zopt, the device wiuld like to see.
If you don't have a nonlinear model use Krips method: Calculate Ropt by devidind Vmax-1 (about) by the max current. Then calculate the parallel capacitorto this Ropt from its S22.
Now you have Zopt- the load the device has to see for max power output, use LC elements to match the load.

 

[vfone]

Re: impedance matching

If you know the PA name, go to the datasheet and see what recommends the manufacturer for output match (if is external). Beware, now mostly of WLAN PA’s use internal output match, from where you can go direct to a 50 ohms load.
If you don’t have the datasheet, you have to measure the output impedance of the PA (at Pout = +17dBm), using the Network Analyzer and match this impedance to antenna impedance.

 

[selvaraja]

Re: impedance matching

Hai DJ , vfone,

Is it the method you mentioned a applicable if I am implementing in IC using CMOS 0.18 um process. Thank You


regards

selvaraja

 

[jimway]

Re: impedance matching

I am puzzled because in T.H.Lee's book impedance matching for PA is unnessesary due to the efficiency.

 

[vfone]

Re: impedance matching

selvaraja,
Doesn’t matter what process you are using. The PA needs an output match to get the performances.
For WLAN is not enough to get the Power and Efficiency. Very important is to pass EVM.
Output match topology and tuning it will affect all these three parameters. Nobody can give you the components values for the output match. These are particular for each PA design.