load pull s22

always design the matching in output of PA for optimum load impedance , which convert the 50 ohm to the optimum load impedance of the transistor

khouly

In principle, both i/p and o/p should be matched, though not necessarily 50/75ohm.

Hi,

It's better if your output is matched then you get more exploit your amp, your transfer more power to the load if not your amp will warm up and else...


David

In principle matching is always good but I find really difficult you'll be able to do that in a power amplifier.
When designing for high output power mismatch must be tolerated mainly, but not only, to avoid oscillation.
Max

But if we need to insert a band selection filter between PA and antenna.
In case the filter is not matched, the frequency response would change, right?
Is it a concern?

yeah it will change , in my designs we always use a matched filter or we design the matching circuit , so the PA works well with the filter

most of the filters in the market these days , is matched for 50 ohm , so u won't need the matching circuit
i am using SAW filters they are matched already

khouly

Hi,

But generaly SAW filters have a problem with power [max power as I find is about 30dBm]in unputs so putting them in PA output not will be a problem?

David

yeah , most of the SAW devices are for mobile devices which max out is limited to 30 dbm or eveb 28 dbm

khouly

well, if it's a general product, matching to 50ohm is necessary. However, if you know what's the load, you need to match the load.
Anyway, the match is necessary.

I do not fully agree. From a theoretical point of view, a power amplifier should be designed for maximum efficiency. This means the load impedance should be chosen for optimum efficiency and minimal loss in the PA, meaning longer battery lifetime or consumption. Load pull measurements can identify this optimum impedance.

From a practical point of view, I agree. Most of the time commercial antennas and filters are designed for 50 ohm, so it is a good choice to stick to 50 ohm from a cost budget point of view.

I try again.
At low freq. ... let's say below 2 GHz matching input and output could be reasonable (using buffer!) even if I don't think you can expect more than 15 dB unless you want to design an oscillator :D .
At higher freq. things will be even more difficult for the same reason.
This can be checked looking at some data sheet of PA.
Max

Hi,

By definition, matching is connecing two circuits the source and the load together via a coupling device in such a way that the MAXIMUM transfer of energy occur between the two circuits.

This will maximize power transfer from source to load and will improve the signal to noise ratio. Right?

Let Assume that transistor(Zs=50) output power is traveling on a transmission line with Zo=50Ω and its connected a load Zl=75Ω. Since Zo ≠Zl then some of the power will reflect back to the source(Zs) and the power delivered to the load (Zl) is not what we expect. To correct this we have to design a matching netwok so that maximum transfer can be achieved. I spend much time designing matching network than any other part of the circuit because we can tweak this network base from our design requirement such as MGA,HGA, LNA, MNA,BBA.


Goodluck