DDR3 pattern for AM3874

Michi Yama

Guru 10030 points

Other Parts Discussed in Thread: AM3874

Hi,

My customer is designing AM3874 board with DDR3 now. And they have some question regarding pattern length.

Please see the attached file. And give me answer. 3302.Question for DDR3 pattern.ppt

Quick reply is helpful for me.

Best reagrds,

Michi

over 12 years ago

0 Biser Gatchev-XID over 12 years ago

TI__Guru**** 393215 points

Hi Michi,

On the PPT you sent:

Q1: This is very precise indeed. You will get also very close results if adding via radius. The difference will be too small to be of any account.

Q2: What is this resistor? If you are referring to the EVM schematics, there are 22Ohm resistors on the DM lines, which length should be taken into account. On the EVM there are also 0Ohm resistor arrays on the Data/DQS lines, which can be removed from the design if you don't need them as access for measurements. If included, their length should also be taken into account.

Best Regards

Biser

0 Michi Yama over 12 years ago in reply to Biser Gatchev-XID

Guru 10030 points

Dear Biser-san,

Thank you for your quick reply.

Regarding Q1, if pattern is connected to the differenrt layer, total length must be included the height(between layer and layer), I think.

Do you know the calculation in case of the height is included?

I appreciate your quick reply.

Best regards,

Michi

0 Biser Gatchev-XID over 12 years ago in reply to Michi Yama

TI__Guru**** 393215 points

Hi Michi,

Yes, in order to be precise the via height should be included in the calculation.

Best Regards

Biser

0 Michi Yama over 12 years ago in reply to Biser Gatchev-XID

Guru 10030 points

Biser-san,

Thank you for your quick reply.

Regarding the height, is it just height from via to via? Are there some restriction?

Best regards,

Michi

0 Biser Gatchev-XID over 12 years ago in reply to Michi Yama

TI__Guru**** 393215 points

I don't understand what you mean.

0 Michi Yama over 12 years ago in reply to Biser Gatchev-XID

Guru 10030 points

Dear Biser-san,

Thank you for your support.

I attached powerpoint file with my new question. Plese see the attached file. And give me your advice.

8750.Question for DDR3 pattern2.ppt

Quick reply is helpful for me.

Best regard,

Michi

0 Biser Gatchev-XID over 12 years ago in reply to Michi Yama

TI__Guru**** 393215 points

Hi Michi,

I understand now what you mean: Total length A" = B"+ C"+D"+C"+E? or Total length A" = B"+"via"+C"+D"+C"+D"+"via"+E"?

The second one is more precise of course, but it should be: Total length A = B+via radius+C+D+C+via radius+E. However I don't think that via diameter will have much influence on total length. There is a tolerance for matching lengths, after all. Please tell your customer that it is desirable to use as few vias as possible on DDR3 lines.

Best Regards

Biser

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DDR3 pattern for AM3874