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There is a pulse going through a transmission line. There is a phenomena where if we put a pulse through a transmission line then after it reaches the IC we can have ringing instead of good pulse. In LTSPICE simulation connector is represented as pulse voltage source of 6V with resistor in series.

Transmission line is represented as RLCG. The load is 2 Ohm because 6V/3A=2Ohm. As you can see i could not get oscillations from this transmission line. I was expecting to see a picture as shown in the end, instead I got in the plot saw shapes which very stable response.

Where did I go wrong with this simulation?

[![enter image description here][1]][1]

[![enter image description here][2]][2]

Wikipedia

enter image description here

Eric Bogatin book on signal integrity

Editied:i removed photos from books and wikipedia because i still need to learn how to properly give credit.

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    \$\begingroup\$ Josh23 - Hi, As you're new here, please see the tour & help center for the main site rules. || Please note that if a post copies or adapts content (e.g. text, image, photo etc.) from elsewhere, that content must be correctly referenced. As a minimum, for online material, the original source webpage / PDF / video etc. should be named & linked (see that rule about references for books / articles etc.). Therefore please edit your question to name & link the original source of each copied/adapted image (and remember it's your responsibility to do that in future). Thanks. \$\endgroup\$
    – SamGibson ♦
    Commented Nov 24, 2023 at 19:08
  • \$\begingroup\$ Hello Sam ,i have tried to add description to the photos but it ruined the display of them .so i deleted them leaving only LTSPICE simulation photo.Could you please give me a link on a manual how to post photos and present links together on this fiorum? \$\endgroup\$
    – Josh23
    Commented Nov 25, 2023 at 5:57
  • \$\begingroup\$ Give that a look. Text between references is ignored, or breaks the references (embedded links). Put the text with the respective images. I'm not sure if I placed it appropriately; please review for accuracy. \$\endgroup\$
    – Tim Williams
    Commented Nov 25, 2023 at 6:34
  • \$\begingroup\$ Question: where does 6V/3A = 2Ohm come from? This relation is not an explanation; it's just substituting one arbitrary number with two arbitrary numbers. Where did L and C come from, can you show your calculations for them as well? \$\endgroup\$
    – Tim Williams
    Commented Nov 25, 2023 at 6:37
  • \$\begingroup\$ @Josh23 - Hi (a) Pages about SE editing help include here, and here from the FAQ. (b) I see you're getting help from another site member, so I won't get involved unless needed. (c) It's not enough to say that an image source was, for example, "Wikipedia". The source name should give a page title e.g. "Wikipedia - Resistors" & if the source is online, give the page link. If the source is a printed book then see the site rule I linked before. It explains about a citation's contents. TY \$\endgroup\$
    – SamGibson ♦
    Commented Nov 25, 2023 at 6:57

1 Answer 1

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Where did I go wrong with this simulation?

You lumped all the cable's distributed capacitance and inductance into two components and that won't cut the mustard when looking at discontinuity reflections. They are called reflections btw and, although they look like ringing, they are not: -

enter image description here

Also, you appear to be expecting a 50 Ω cable but, the characteristic impedance is more like 316 Ω. You can of course you LTspice's built in transmission line but, don't ask me where it is because I don't use LTspice.

You also need to put links in your question for the images so you can credit them.

Ringing or reflections

Here is a simulated 1 metre, 50 Ω transmission line driven by a 5 MHz squarewave having a zero ohm source impedance. The cable has a 300 Ω termination: -

enter image description here enter image description here

Those effects on Vout are not ringing but reflections traveling back and forth down the cable summing with each other positively and negatively. And, this isn't some theoretical effect either. I was shown this at college in the 1980s where a prof set up an experiment with a few metres of coax just so that we didn't confuse ringing (an LC filter for example) with the reality about reflections.

Here's what happens when the load is significantly lower (10 Ω) than the characteristic impedance of the cable: -

enter image description here

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    \$\begingroup\$ When there are reflections at source and load, it does produce a ringing behavior and you will find plenty of authoritative sources that name it that way. Even if you personally disagree with the term, telling OP the term is wrong will only confuse them when they're reading material from other sources. \$\endgroup\$
    – The Photon
    Commented Nov 24, 2023 at 17:45
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    \$\begingroup\$ For example here is Eric Bogatin discussing "ringing from unterminated lines". Here is Howard Johnson saying that "Terminations exist to control ringing". \$\endgroup\$
    – The Photon
    Commented Nov 24, 2023 at 17:50
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    \$\begingroup\$ @Andyaka, 1. Bogatin and Johnson are two of the most authoritative figures in the field of signal integrity. They're the authoritative authors Wikipedia should be citing for appropriate articles. 2. It's not a matter of one or the other: reflections are the cause, ringing is the effect. 3. Just because the ring signal has harmonics doesn't mean it's not a ring signal. And it will never be perfect step events because the (real-world) signal doesn't have infinite bandwidth. \$\endgroup\$
    – The Photon
    Commented Nov 24, 2023 at 22:17
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    \$\begingroup\$ @Andy aka - Really??? You have 442,000 reputation points, opine all the time on SI issues, yet you claim to have never heard of Drs. Eric Bogatin and Howard Johnson? How 'out Lee Ritchie (The Speeding Edge)? All acknowledged experts (as The Photon said) in SI matters. And all use the term "ringing" to describe the effects discussed here. \$\endgroup\$
    – SteveSh
    Commented Nov 25, 2023 at 1:32
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    \$\begingroup\$ @Andy aka - I finished my university level schooling in the mid 70's. Signal Integrity was not much of a concern back then. And I never took an SI or related course. All my knowledge and experience with SI has been OJT (On The Job) training. I only came across Bogatin, Johnnson, Ritchie, and others around the turn of the century when SI became an issue with the increases in IC and system level clock rates. \$\endgroup\$
    – SteveSh
    Commented Nov 25, 2023 at 11:51

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