What are the consequences of a source terminator resistor (placed in series with the output) that is too high of a resistance value? Is it just a slower rise time at the input, or are there other consequences? Do I make ringing/reflections WORSE at the input if the source terminator is too high?

I am wondering what can go wrong if I just put a source terminator resistor in series with an output that makes the series resistance greater than the characteristic impedance of a short transmission line? (When I say transmission line, I'm talking about wire of a few inches, paired with a ground wire of same length.)

  • \$\begingroup\$ It sounds like you're asking about terminating a transmission line at first, but then talk about a GPIO pin. I can't make out what you're asking, and even what you think "terminating" actually means. \$\endgroup\$ Dec 13, 2016 at 19:27
  • \$\begingroup\$ I would not try to put 50uA through a transmission line. \$\endgroup\$ Dec 13, 2016 at 19:28
  • \$\begingroup\$ @OlinLathrop - You're right, I will edit my question to get rid of the GPIO pin nonsense. My question should be simple: What happens when the source terminator resistor is too large of a resistance value? \$\endgroup\$
    – acker9
    Dec 13, 2016 at 19:30
  • \$\begingroup\$ See figures 3 and 4 of this application report. \$\endgroup\$
    – CL.
    Dec 13, 2016 at 20:34
  • \$\begingroup\$ Is the transmission line terminated in the characteristic impedance of the line? Most likely, if this is a digital signal only travelling a few inches, then it doesn't matter very much. You may not need the series termination at all. \$\endgroup\$
    – user57037
    Dec 14, 2016 at 2:49


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