Microwave Office: Reference planes of RF Power Transistors

[Andrew77]

pdf microwave office

Every time I simulate a rf power amplifier from microwave office I get a little difference from the datasheet Test circuit (Freescale, Infineon) etc. There is always a shift of frequency of about 100-200 MHZ for 2 GHz.
I expect that the problem is the reference planes of the transistor

Could anyone confirm this or give me a better solution to understand

Thanks

 

[Element_115]

Re: Microwave Office: Reference planes of RF Power Transisto

I'm not sure about MWO's workings, but when you use RF Power Amps
you have to get Good Models form the IC maker. At high power a PA's
non-linearities do not behave like most linear models. As you get close
to the PA's 1dB Compression point the internal characteristics of the IC
will change considerably.

 

[septipop]

The data You find in the Datasheet is in most the cases for small signal (I mean the S Parameter and the .s2p file that You use for simulation). If You work at large signal, You have to use the large signal Parameters, which are not every time available, or the large signal model, which is even rare to find!
On other hand, Your simulation is a "clean" circuit, without any other interference. The data You see in the Datasheet is measured in real conditions, on test boards, on which parasitic effects come into action and their effect encreases with the frequency. These parasitic effects (magnetic and electric coupling, parasitic L of the C and viceversa, parasitic L and C of the soldering pads, etc.) You cannot take into account or estimate during the simulation. Even if You try, You'll never succeed in simulate all of them and everytme the practical result will have a slight or considerable difference in comparation to the practical circuit. Take in mind that always after You implement a circuit in accord to the simulated best results, You'll have to optimize it, because the reality always beats the theory!

 

[Manjunatha_hv]

Re: Microwave Office: Reference planes of RF Power Transisto

Hello Andrew77,

The shift may be due to lot of factors such as..
the first foremost issue is you need to have good device models for all Linear/Nonlinear devices you use, try to use the Spicemodels...
check the individual device model charcteristics againest the datsheet details if they are matching or almost matching then proceed with the design...
Or
You can go to Modelithics who provides good models & use with Microwave Office
There are Nonlinear models for Mitsubishi devices for using with MWO from Modelithics
**broken link removed**

The second issue is the dielectric substrate parameters & the layout design...
& if lot of discontinuty & problems and even operating above 1GHz simualte the matching network using Electromagnetic simulator...
Use realistic substrate parameter values & do yield analysis before going for proto...

Finally, If you still have the problems then send the measured data & MWO project file to AWR support they will help you or send it to me at manjunatha_hv@ieee.org

With S-parameter file you can do Small Signal analysis,
such as S-parameters, S11, S22, S21, etc,
Input/output impedance, Gain, NF, Stability of the device based on the meared data at perticular bisa conditions...
https://www.rfcafe.com/references/a...sign-of-RF-Microwave-Amplifiers-copyright.pdf
You can design PA using S-parameters, the procedure & a article is appended below...
First-Time-Right Design Of RF/Microwave Class A Power Amplifiers UsingOnly S-Parameters

other usefull documents on PA design documents using MWO...
www.rfpoweramp.com/papers/rfpa_mwo.pdf

www.polyfet.com/HFE0503_Leong.pdf

**broken link removed**

**broken link removed**

---manju---

 

[Andrew77]

Re: Microwave Office: Reference planes of RF Power Transisto

Hello manjunatha_hv!

you are right when you say that I need a good model in order to simulate a RF power transistor, this is not the first time i simulate and test a PA with frequency > 1 GHz. For my projects I start from the datasheet's pcb and I simulate this by using the non linear model provided by the MWO in its library element browser. This is not a small signal model because I can test the Linear Power, P1dB, Output Impedances, PAE, etc...

The data are quite close to the datasheet pcb results except of the frequency shift of about 100-200 MHz. I'have read from an AN: **broken link removed** (Accurate Simulation Models. Yield High-Efficiency Power Amplifier Design) this happens because of the transistors ' reference planes which are not well defined. Infact when I simulate I have to add a longer or a shorter I/O Microstrip Lines in order to "Match" the simulation to the pcb datasheet results.
Thanks for your help