Hello,
I am currently working on a project which deals with DDR SDRAM. Iam trying to figure out how important is the process of "termination" on an IC. What are the types of terminations? What is 'On die termination'? Can anyone explain it to me in simple terms?
Thanks
P.S: I'm not a geek. I'm just a beginner. Please bear with me if my questions are silly.

 

Hi,

Your question is general and would require pages to properly explain. Termination is important when the length of wire traversed by a signal is roughly the same as the length of the signal's pulse edge. Some say if Length of Trace >= Length of Pulse Edge/4. This is a signal integrity issue. "On Die Terminaiton" means the termination element is in the particular IC, and not added to the circuit board, which would be "On Board Termination" For digital signals, termination typically consists of resistance added to a trace that matches the trace impeadance, which if properly done, attenuates reflections, quashes ringing, etc.

 

The idea of termination comes from the study of transmission lines. In the early days of digital logic the frequencies were low. Typically in the 300 kHz to 3 MHz range. The wave length of these frequencies is measured in the hundreds to thousands of meters.

As the frequencies rose into the GHz range the wavelengths went the other way to ever smaller dimensions. In that regime every PCB trace and wire in a harness becomes a "transmission line". In a transmission line there are at least four interesting conditions.

1. Open, Infinite impedance
2. Short, Zero Impedance
3. Characteristic Impedance
4. Any Other Impedance

In the case of termination with the characteristic impedance of the transmission line there will be no reflections from the load back to the source and the system will behave nicely. In all of the other cases there are increasing levels of negative consequences.

http://en.wikipedia.org/wiki/Transmission_line