Matching network Proof
I am doing an assignment regarding the LNA design.Theres a question which ch asks that I have to prove that the input matching network is not necessary for the specified problem.
According to the problem, the source and load impedance are given as 50 ohms.
Would be great if someone guides me to go about in solving the problem
Santom
You will have to show that with the specified load either the input impedance of the transistor is 50 ohms or that the source impedance which produces the minimum noise figure is 50 ohms.
HI..
Thanks for the reply.But unfortunately I was not able to capture as what you were trying to explain me.Would be really great if you elaborate on that answer.
Thanks again for your reply,
SAntom
your goal is to show that this particular transistor does not need an input matching network. This network is not needed if the input impedance is already 50 ohms and thus will produce maximum gain with the 50 ohm source.
First read about Gain Circles and N Opt Circles Pozar's Microwave Engineering CH 10.
So you will understand what Flatulent was explaining.
Look at this LNA data sheet (on pg 8).
http://www.datasheetdir.com/go/-bxj-xk-xxnkmn.pdf
You will see that the input matching circuit is being described by a Noise figure
"Circle". Now if you look at the Noise Circle NF = 1.6dB you will notice that 50 Ohms
is in/on that circle ! So if you just use a 50 Ohm line to inject the input signal you LNA
will give you NF = 1.6 . Now we assume that you input signal will becoming from
a 50 Souce (i.e a Sig Gen).
Now go to the Data sheet of your LNA Amp and see if you can answer your question.
Hope this helps !
Cheers
Develop the circuit as per the PCB guide lines by the manufacturer and test for RL.
If RL is OK then you can confirm that they are matched to 50 ohm and you need not to do any thing.
If you feel that you need to get better RL then you need to measure the S-para and go 4 simulation and optimize the circuit.