4 ms·

In the spirit of times - does anybody know what room-temp supercoductors would do to the transmission lines, like DP/HDMI? Would 0 resistance have positive inf

by jagrsw 3y ago

In the spirit of times - does anybody know what room-temp supercoductors would do to the transmission lines, like DP/HDMI? Would 0 resistance have positive influence on signal degradation/coherence (ie. increasing maximum cable lengths or their reliability), or maybe it's already limited by various forms of capacitance/inductance or other problems in cables?

Waterluvian 3y ago
Assuming you could produce viable consumer cables that are superconductors, my understanding is that there would be no signal loss, so your hypothetical cable could have infinite length. Digital is digital so this would be true for any data use case. Maybe someone smarter can chime in about how electromagnetic interference affects or doesn’t affect a hypothetical “superconductor cable.”
- mycall 3y ago
  The longer the cable, the longer duration loopback signals take. This can affect timing of any synchronous specification. If it is too long, it could be out of scope of the spec and thus stop working. Maybe you can solve this with a transceiver MITM device.
  - Waterluvian 3y ago
    Oh right I forgot about that! So yeah… probably longer than you’d need but not infinitely long. Unless the protocol is fine with it.
- Filligree 3y ago
  Superconductors only have zero resistance when measured in DC. AC still faces impedance, high frequency AC like DisplayPort especially so.
mschuster91 3y ago
Line length would not be limited any more in theory, but it's not like you can do ridiculous length even with a HTSC wire. The most obvious factor is protocols, you can't get faster than light which means protocols with a tight response timeout won't work out. The second one is capacitance, as most transmission is something very closely resembling AC, so IIRC even at zero resistance you'd still have a capacitance between the lines and a resulting reactive power.
stn8188 3y ago
This is a really great question. If you had a perfect conductor in air, then yes you would have no attenuation (or "insertion loss", one common term used in Signal Integrity). Real transmission lines (cables, PCB traces) use dielectric insulating layers adjacent to the conductors. These dielectrics have a property called permittivity which affects what we call "dielectric loss". Essentially, transmission line loss can be broken into conductor loss (resistance, skin effect, etc.) and dielectric loss (energy lost by causing physical rotation in the dipoles of the dielectric material). A perfect conductor would have zero conductor loss but would still have some of this dielectric loss. I covered the concept a little bit in a webinar recently [0] but SI guru Eric Bogatin really boils it down best. In this [1] equation for loss estimation in a PCB trace, you can see the conductor and dielectric portion of loss on either side of the "plus sign". The left part is the conductor loss and is proportional to the square root of the frequency. The right part is the dielectric loss and is proportional to the frequency of the signal, as well as proportional to parts of that permittivity (Dk and Df in that equation). To answer your question though, it absolutely would allow for much longer cables since you eliminate one part of the loss. Sorry for all the ridiculous detail, if you're still interested in the topic please feel free to reach out for more info! Contact info in my profile and at [0]. [0] https://wiki.shielddigitaldesign.com/High_Speed_Design_Wiki/Software_Tools/Simbeor.html https://wiki.shielddigitaldesign.com/High_Speed_Design_Wiki/... [1] https://www.edn.com/loss-in-a-channel-rule-of-thumb-9/ https://www.edn.com/loss-in-a-channel-rule-of-thumb-9/
- azzentys 3y ago
  That man is really good at teaching/explaining SI concepts. He was my professor at my university and taught High Speed PCB design class. Lots of learning like the one you described!
- LASR 3y ago
  The details - I feel like I learned everything I would have from a whole 3-credit university course. Thank you.
- nine_k 3y ago
  I wonder if a coaxial cable with the outer tube made superconducting would make a difference.
hatsunearu 3y ago
superconductors are lossy at AC (less so than regular conductors, but significantly above negligible) a very large bulk of the loss is through dielectric loss too. that one you can't get rid of with superconductors.
- Cerium 3y ago
  No such thing as a super insulator?
  - stn8188 3y ago
    vacuum :)
    - hatsunearu 3y ago
      Vacuum is actually a horrible insulator, like in practice.
dale_glass 3y ago
You don't have to go that fancy, you could just use fiber optics right now. You can get insane bandwidths out of quite cheap and manageable cable. Eg, you can put 100 Gbps down a single strand. Not enough? Try a MPO cable with 12 of those. Maximum length is effectively unlimited.
Filligree 3y ago
Note also that superconductors only have zero resistance to direct current. AC, including and especially any form of high frequency signaling, still face impedance.
rasz 3y ago
Im sure a plethora of high end audio vendors will come out with whole lines of superconductor digital audio/video cables with higher sound clarity and wider soundstage precision.

by jagrsw 3y ago

Waterluvian 3y ago

Assuming you could produce viable consumer cables that are superconductors, my understanding is that there would be no signal loss, so your hypothetical cable could have infinite length. Digital is digital so this would be true for any data use case. Maybe someone smarter can chime in about how electromagnetic interference affects or doesn’t affect a hypothetical “superconductor cable.”

mycall 3y ago
The longer the cable, the longer duration loopback signals take. This can affect timing of any synchronous specification. If it is too long, it could be out of scope of the spec and thus stop working. Maybe you can solve this with a transceiver MITM device.
- Waterluvian 3y ago
  Oh right I forgot about that! So yeah… probably longer than you’d need but not infinitely long. Unless the protocol is fine with it.
Filligree 3y ago
Superconductors only have zero resistance when measured in DC. AC still faces impedance, high frequency AC like DisplayPort especially so.

mschuster91 3y ago

Line length would not be limited any more in theory, but it's not like you can do ridiculous length even with a HTSC wire. The most obvious factor is protocols, you can't get faster than light which means protocols with a tight response timeout won't work out. The second one is capacitance, as most transmission is something very closely resembling AC, so IIRC even at zero resistance you'd still have a capacitance between the lines and a resulting reactive power.

stn8188 3y ago

This is a really great question. If you had a perfect conductor in air, then yes you would have no attenuation (or "insertion loss", one common term used in Signal Integrity). Real transmission lines (cables, PCB traces) use dielectric insulating layers adjacent to the conductors. These dielectrics have a property called permittivity which affects what we call "dielectric loss". Essentially, transmission line loss can be broken into conductor loss (resistance, skin effect, etc.) and dielectric loss (energy lost by causing physical rotation in the dipoles of the dielectric material). A perfect conductor would have zero conductor loss but would still have some of this dielectric loss. I covered the concept a little bit in a webinar recently [0] but SI guru Eric Bogatin really boils it down best. In this [1] equation for loss estimation in a PCB trace, you can see the conductor and dielectric portion of loss on either side of the "plus sign". The left part is the conductor loss and is proportional to the square root of the frequency. The right part is the dielectric loss and is proportional to the frequency of the signal, as well as proportional to parts of that permittivity (Dk and Df in that equation). To answer your question though, it absolutely would allow for much longer cables since you eliminate one part of the loss. Sorry for all the ridiculous detail, if you're still interested in the topic please feel free to reach out for more info! Contact info in my profile and at [0]. [0] https://wiki.shielddigitaldesign.com/High_Speed_Design_Wiki/Software_Tools/Simbeor.html https://wiki.shielddigitaldesign.com/High_Speed_Design_Wiki/... [1] https://www.edn.com/loss-in-a-channel-rule-of-thumb-9/ https://www.edn.com/loss-in-a-channel-rule-of-thumb-9/

azzentys 3y ago
That man is really good at teaching/explaining SI concepts. He was my professor at my university and taught High Speed PCB design class. Lots of learning like the one you described!
LASR 3y ago
The details - I feel like I learned everything I would have from a whole 3-credit university course. Thank you.
nine_k 3y ago
I wonder if a coaxial cable with the outer tube made superconducting would make a difference.

hatsunearu 3y ago

superconductors are lossy at AC (less so than regular conductors, but significantly above negligible) a very large bulk of the loss is through dielectric loss too. that one you can't get rid of with superconductors.

Cerium 3y ago
No such thing as a super insulator?
- stn8188 3y ago
  vacuum :)
  - hatsunearu 3y ago
    Vacuum is actually a horrible insulator, like in practice.

dale_glass 3y ago

You don't have to go that fancy, you could just use fiber optics right now. You can get insane bandwidths out of quite cheap and manageable cable. Eg, you can put 100 Gbps down a single strand. Not enough? Try a MPO cable with 12 of those. Maximum length is effectively unlimited.

Filligree 3y ago

Note also that superconductors only have zero resistance to direct current. AC, including and especially any form of high frequency signaling, still face impedance.

rasz 3y ago

Im sure a plethora of high end audio vendors will come out with whole lines of superconductor digital audio/video cables with higher sound clarity and wider soundstage precision.