My doubt pertains to the usage of termination resistors. This is a continuation of the discussion I saw in this link - Termination resistor.

I understand that any transmission line can be simulated using a set of LC components (viz a number of tank circuits).

When it says a transmission line, it can also mean a microstrip, right ? Because a microstrip can also send a high speed signal, right ?So, does that mean I will need a termination resistor even in a microstrip ?

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    \$\begingroup\$ If you can live with reflections that are produced when the termination is not there, you dont need it \$\endgroup\$ – PlasmaHH Jan 28 '16 at 14:04
  • \$\begingroup\$ @PlasmaHH. So even microstrips need a termination resistor you mean ? Now, wouldnt that just ground the signal ?This is nothing buta resistor from the microstrip to ground, right ? \$\endgroup\$ – Board-Man Jan 28 '16 at 14:13
  • \$\begingroup\$ They don't "need" termination, if the results of omitting them are negligible to the performance of the circuit. \$\endgroup\$ – rdtsc Jan 28 '16 at 14:22
  • \$\begingroup\$ @Board-Man: microstrips don't really work like the classical electrical connections where you want currents flow, it is more that you direct electric fields in certain ways. As such you have to take the load impedance into account and according to that design it in a way that you don't have signals (e.g. reflections) going into places where you don't want them, which sometimes means shunting them to ground so they do not bounce. But if that bouncing field gets attenuated enough on its way back anyways, there is no need for it. \$\endgroup\$ – PlasmaHH Jan 28 '16 at 14:22

A microstrip is a variant of a transmission line. Just like a piece of Coaxial cable it a variant of a transmission line.

A transmission line transports a signal (from A to B) without affecting it (except for some attenuation) but only when used properly.

How to use a transmission line properly ?

  • At the input side use the proper source impedance when applying the signal.

  • At the output side use the proper termination impedance to ground.

If these conditions are not met, you will get signal reflections.

For example, if you do not place the proper termination at the end of the transmission line, part of the signal reflects back and distorts your signal. When the proper termination resistor to ground is present, it will appear as if the transmission line "goes on for infinite length" and there will be no reflections.

This also applies to a microstrip line so yes, you need to terminate it properly. Unless you want or you can tolerate to have signal reflections of course !

  • \$\begingroup\$ Ought to mention the special case that when there's a single point of reception, you can use a series termination resistor at the sending end. The reflection from the o/c receiving end is part of the mechanism of getting the correct signal. \$\endgroup\$ – Neil_UK Jan 28 '16 at 14:34

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