difference routing length between microstrip and stripline

[diegopm]

Hello,

I have a question about microstrip and stripline in ddr3 or SI.

What happens with difference routing length between microstrip and stripline?

For instance, the match length in ADDR CMD CONTROL is 20 mils, but it is easy to get a difference between microstrip and stripline about 1 cm, so this results in skew of tens of ps.

Is there some rule for this dispersion between microstrip and stripline?

I have used a simulator and I had 50ps of dispersion in the worst case.

What is the maximum skew in DDR3 flyby 800MT/s?

BR

[robertferanec]

diegopm, I try to keep the length routed on TOP/BOTTOM similar between tracks in one group, but we do not length match it in memory layout. I have not seen any problems with it. (In many designs it is very difficult or it may be even impossible to do that).

Always, when I am not sure or if something is not specified I have a look at some other designs. In your case, I recommend you to have a look at JEDEC memory layouts - you can download the designs and compare microstrip and striplines between signals: https://www.fedevel.com/welldoneblog...yout-examples/

I checked one of my design guides (AMD) and the length matching of ADD/CMD/CTL is done in tolerance +/- 45ps (1333MT/s). But you really may want to follow design recommendations of the chip which you are using (but I guess they do not have it, otherwise you would not be probably asking).

[Ershad]

Hi Robert,
In the Schematics and PCB design course of Lesson 1 at 54:25 of the video, the example values of stripline are used as input to the Microstrip cross-talk calculator during explanation. Is this valid ?. Please clarify...

[robertferanec]

Very good catch! You are right. To get the values for the specific case from the document, the Stripline calculator should be used (or the numbers from the microstrip table should be used). I believe I used the table because it directly shows the dimensions, so I used them for the demo.

[Ershad]

Ya got it...