Why termination is required

Since current typically flows from one side of an RS driver through the termination network, then through the other side of the driver, by placing a series capacitor the steady state current goes to zero. The two caveats of this type of termination are that it requires one extra component on each termination network, and the series resistor and capacitor introduce a resistor-capacitor RC delay. The RC time constant will slow the rising and falling edge of the differential signal and limit the maximum data rate of the network.

For optimal signal integrity, it is always best to match the differential-mode characteristic impedance of the cable with a termination of equal impedance. But if you take the proper steps, it is also possible to successfully implement AC terminations or avoid termination altogether.

As always, log in and leave a comment if there are any RS topics you would like to hear more about. This is true that a reflection is where some of the energy of the signal literally returns back up the line, which can then constructively or destructively interfere with the next bits propagating down the bus. You can find some discussion in section 5 on page 7 of this app note www. It explains how to choose the cap value. If you still have questions, you're welcome to post them on e2e.

We would love to continue the discussion. Thanks for the question. Below is an app note that has some oscilloscope screen shots of an example set-up in the lab. Also, I would recommend placing any additional questions on the industrial interface forum for product specific help from the current applications team.

Below is a link to the forum:. Site Search User. Share Contact author Subscribe by email More Cancel. Similar topics. RS basics: When termination is necessary, and how to do it properly. Digital Multimeter Instrumentation. Counter Timer Instrumentation. Digitizer Instrumentation. All Measurement Products.

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All Power Supplies Products. Bus Interfaces. Bus Expanders. ARINC All Bus Interfaces Products. Wavetek Replacements. AC signals that travel along a wire get reflected at its ends. This reflected signal mixes with the "real" signal and causes interference. Termination usually means to put a resistor at the end; this makes the line end behave like an infinite length of wire with no end, so no reflection. The value of the resistor depends on the impedance of the line. This is why there is a specific termination resistor value that has to be used for a specific type of line or bus.

Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. What and Why's of termination? Ask Question. Asked 6 years, 5 months ago. Active 6 years, 5 months ago. Viewed 12k times. He uses mechanical waves to demonstrate reflections, termination and impedance changes.

Add a comment. Active Oldest Votes. The wave should move from left to right: As you can see, piece no 15 encounters an upward force and so is accelerated upwards. What happens at the wall? What if the rope is not fixed at all? What if your buddy holds the second end? What does it have to do with electronics? EDIT: Searched for it yesterday, but didn't find it. EDIT2: I had some fun writing a simulation.

I like all the answers but i understood them well, only after reading your explanation. Do you know from where to start with all the basics to understand digital communications. Nick Johnson Nick Johnson 7, 3 3 gold badges 25 25 silver badges 43 43 bronze badges.

In lossy lines realistic ones , there are also series resistance and shunt conductance in the ladder. Because it is a series inductance, at low frequencies a very long cable doesn't look like a 50Ohm resistor, it looks like whatever the cable series resistance. At high frequencies it looks like a 50Ohm. I believe my post addresses the frequency issue - I stated that it looks like a 50 ohm resistance only while the signal is propagating.

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