Quarter Wavelength Impedance Matching
Вставка
- Опубліковано 22 лип 2024
- What is a quarter wavelength transmission line and how should PCB designers use it? We've gotten a lot of RF design questions, some specifically centered around this area. Technical Consultant Zach Peterson explores this topic, how it relates to impedance matching and more.
0:00 Intro
0:48 What is Impedance Matching?
3:29 Quarter Wavelength Transmission Line Properties
7:34 Complex Load Impedance
11:09 Win a T-shirt!
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Alright everyone this contest is over and we have a winner! The answer is for this specific problem is: the length of T line 1 is 0.0292*lambda, the impedance of the quarter wavelength line is 35 Ohms.
There is actually a universal answer that I'll outline in an upcoming video when we announce the winner. Hint: it's always an 1/8th wavelength line!
Sir thank you so much for teaching quarter wave transfor. from Turkiye. Best
My favorite subject. T-lines!
Well presented
Hi Sir I like the way to present these topics related to RF and I am waiting to learn more.
Below are the values I got for the question -
L1 = 0.143lambda and Zo2 =28.5043.
Contest is officially closed! We'll announce the answer and winners very shortly!
Hi Zach, I got 0.0291 lambda :-)
Also, it can be solved with single TL of Zo=33.94 (rounded 34) with single length=0.31227 lambda (0.312) 12% longer, but wider BW and less reflection...
Correct! You can also watch the derivation of answers here:
ua-cam.com/video/euLADxkjG98/v-deo.html
Hey Zach, love your videos!
I have a question for you to make a video about it. I've been told by engineers to pour power planes under all the components that references to that plane potential.
Meaning, they want the plane to exceed the vias related to the components and surround all of them because of parasitic capacitance that the plane have on the interconnects of that circuit.
Can you please make a video explaining about the parasitic capacitance of power planes? thanks!
Hello Zach, here's my result to your challenge. I found that l1 = 0.029*lambda and Z02 = 35 Ohm.
I normalized the load impedance to 0.5 - j*0.14 then used a Smith chart to find that the input impedance becomes purely real with a T-line length of about 0.029*lambda. This normalized input impedance was approximately 0.49, denormalized to 24.5 Ohm. Using Zin = Z0^2 / ZL for a quarter-wave impedance transformer, I obtained Z0 = 35 Ohm. Let me know what you think!
My cat thinks the same, but you made a terrible mistake referring to the Smith chart. Zach doesn't like the Smith chart so my cat is terrified right now...
I got Smith's charts flashbacks from my uni exams.
Help
Since I gave the desired impedance of the transmission line connected to the load, you shouldn't need a Smith chart. FYI, I detest Smith charts....
My cat (and he always watches Zach with interest) tell me: 35 Om length/4, after 50 Om length/34.
The length=pi/4 (45 degree), the characteristic impedance (Zo2= 50 ohm)
Or lambda/8 for the length