Power Amp design using LDMOS FET

[Notorious]

Hi,

I am looking to design a Power Amp using an NE5520379A at 2.4GHz. I am a relative novice at designing RF power amps and am looking for guidance about how to go about matching the amp to 50ohm and the input and output.
I have the S-Parameters for the device and would like to know if there is any good (free) software that can be used to design the matching sections. I have seen some papers on power amp design but they all mention very expensive software (Microwave office etc).

I have had the opportunity to look inside an existing one and noticed a lopad of weird and wonderful looking matching sections etched on to the PCB and was wondering how do they go about working all that out?


I would really appreciate any help, thank you.

 

[nandopg]

Dear Friend,

My advice is for you to choose another device if you have to build a 2.4GHz PA.

Some weeks ago I was assigned to design a 2 Watts PA operating at 2.4GHz. In our company we have as a standard procedure to characterize all the devices prior to proceed with the design. So I did for the NE5520379A. After a load and source pull measurements, this device was characterized to operate at 1.8GHz max with about the same datasheet's specs. However at 2.4GHz the gain rolled off to about 3dB, showing its total inapplicability at this frequency range. So, if you want you can take advantage of this experience and not waste your time as I already did go for another device else.

I don't know about your application but you have several other choices for this frequency and power range.

As to references, I recommend the books from Steve C. Cripps: RF Power Amplifiers for Wireless Communications and Advanced Techniques in RF Power Amplifier Design. These books describe techniques to get your matching circuit without the use of expensive EDA tools.

NandoPG

 

[Notorious]

Thank you for your kind advice. What device would you recommend to do a PA at 2.4GHz?

Also, what method of matching did you use? Microstrips? Any further advice would be great.

 

[nandopg]

Dear friend,

Answering to your questions:

1- To choose a device for your design you would have to answer to the following questions:
What is the voltage supply you have available
Do you have a negative voltage available (to bias a GaAs FET)
What is the maximum current available for the amplifier
What is the operating temperature range for the PA

2- Now for the type of implementation for the matching circuit the questions to be answered are:
What kind of substrate you will use to built your PA on? This answer has a straight connection to the budget for the design.
What kind of physical real estate you have to layout the PA.

For example, normally when you implement a circuit in microstrip line you are aiming productivity, because in the assemble process the components to be placed on the boards would be a minimum, once you have a PCB mask basically corresponding to the circuit's components. What you pay for that is: board's real estate (mainly at 2.5GHz) and the necessity to use an expensive microwave substrate.

By the other hand if you choose to implement the matching using lumped components, you would have more labor in the production process, but the board`s real estate used would be much smaller than in the previous case and also you could use an inexpensive substrate to built the circuit.

Sorry for all of these considerations but there is not a straight answer to your question.

NandoPG