Transmission line with 2x termination

• likephysics
In summary: TL reflection coefficient equation is applied over time for each transition, and maybe use Excel for a quick way to solve for the response to the transition.
likephysics
Trying to work out the match for a transmission line with 2x termination.
Like the one here:
https://ibb.co/p4dY7pF
V1=1
R1=R2=T1=T2=50,
V1 sees R1 and T1. So it is divided to half.
Now you have 0.5V source with a 50 Ohms series impedance(T1) looking into a load that is a parallel combo of R3&T2, which is 25 Ohms.
So voltage at load is (0.5*25/75) = 0.16V.
This further reduces to a voltage source of 0.16v with 25 ohm series resistance and 50 ohm Tline?

(not an assignment, just trying to refresh by knowledge)

I wouldn't call this a 2x terminated TL. It's a lot more complicated than that.

I would use the TL reflection coefficient equation applied over time for each transition, and maybe use Excel for a quick way to solve for the response to the transition. Do you have the simulation results for the waveform seen at the transmitter versus time?

(See the better reply below by Baluncore)

Last edited:
A quick look suggests first simplify the circuit. Since T2 is terminated in a perfect match, T2 can be eliminated and the termination R2, moved to parallel R3, making 25 ohms. Now you have only one line, terminated in Zo/2.

The 1 volt step will appear as a half volt step at entry to T1.
2 ns later, the reflection from the 25 ohm termination will return to the correctly matched T1 input.

You then have a 50 ohm source resistor in series with a 25 ohm load.
So the steady state input to T1 will be 1/3 Vin, as will the output across R2.

dlgoff, DaveE and berkeman
I was trying to figure out the equivalent circuit starting from R3 to the load R2.

Let's say R2=100 and T2=50, then the part from R3 would reduce to
Voltage source of 0.33V with series res of 25 ohm and a T line of 50 ohm?
The 25 doesn't make sense. Since R3=T2, this series res would be 0?
But then what if R3 is not equal to T2.

@berkemen, here's the sim result for ckt earlier.
https://ibb.co/mqmQMrg

likephysics said:
I was trying to figure out the equivalent circuit starting from R3 to the load R2.
The input to T1 is series matched, so it will not return reflected energy from the T1:T2 junction.

When the terminal load R2 is changed from 50R to 100R, both ends of T2 become mismatched, which makes a resonator.

A transient on T2 will travel forwards and backwards until it settles at the terminal state, or is disturbed again by another transient.

The terminal state will be that of a voltage divider where ( 50R // 100R ) = 33R33; is driven through 50R.
33R33 / ( 33R33 + 50R ) = 0.400 Vin.

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• T'Line-termin8.asc.txt
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1. What is a transmission line with 2x termination?

A transmission line with 2x termination refers to a type of electrical circuit that is used to transfer signals or power from one point to another. It consists of two conductors, typically copper wires, that are separated by a dielectric material. The 2x termination refers to the use of two identical resistors at the end of the transmission line to match the impedance of the line and minimize signal reflections.

2. How does a transmission line with 2x termination work?

A transmission line with 2x termination works by using the two resistors at the end of the line to match the impedance of the line. This helps to minimize signal reflections and ensure that the signal is transmitted efficiently from one point to another. The resistors also help to prevent any interference or distortion in the signal, resulting in a more reliable transmission.

3. What are the advantages of using a transmission line with 2x termination?

One of the main advantages of using a transmission line with 2x termination is that it helps to minimize signal reflections, ensuring a more accurate and reliable transmission. It also helps to prevent interference and distortion in the signal, resulting in a clearer and more stable signal. Additionally, using a 2x termination can improve the overall efficiency and performance of the transmission line.

4. Are there any disadvantages to using a transmission line with 2x termination?

One potential disadvantage of using a transmission line with 2x termination is that it can be more complex and expensive to implement compared to other types of transmission lines. Additionally, if the resistors are not properly matched to the impedance of the line, it can result in signal loss or distortion. However, these issues can be mitigated with proper design and implementation.

5. Where are transmission lines with 2x termination commonly used?

Transmission lines with 2x termination are commonly used in various electronic devices and systems, such as telecommunications networks, computer networks, and audio systems. They are also used in high-frequency applications, such as radio frequency (RF) and microwave systems, where signal integrity and efficiency are crucial.

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