REQ: high speed PCB design

[hatemius]

Hello All, could some one help!!
I want to do high speed PCB design to match CPU or Microprocessor to more than external memory!! say two or three.
I want to know how to calculate and terminate both sides plus the other things related to the design.
could any one advice me for ebooks or paper or software or... commands.

 

[electron_boy]

hi hatemius,

u see, ur memory interface is the most critical part of ur digital design. so SI consideration must be done with utmost care. i would suggest u to route ur memory interface signals as a symmetric stripline sandwiched between power (VDDIO) and gnd. this will provide a nice return path for ur high speed switching signal. for this u can refer the paper (10 layer stack up) by Howard Johnson it is available at www.sigcon.com

next coming to terminations, u need to terminate ur address lines near ur source and for the data lines terminating at both the ends will help. but for both address and data u can go for source & end termination.

when u connect more than a single memory device to ur µp u have to have an end termination when u interconnect in a daisy chained fashion. when u bifurcate the line u have to terminate the loads accordingly. for this u can refer Howard Johnson book, Terminations chapter.

the termination is used to match to the characterictic impedence of the line. so u have to terminate with a value equal to ur Z0 but this is not alway true. for this u have to use some simulating tools like Hyperlynx.

 

[Sigma|Six]

Hi, you can look into this site, Polar Si8000 is a good software that can assist you in calculating the PCB track impedance...depends on your requirement, DDR, DDR2 and the PCB layer count. the software can help you to determine the track size, copper thickness, isulation thickness etc...

https://www.polarinstruments.com/

For the Maths in this issue, please refer to

 

[buenos]

Usually a series (source) termination is adviced, but not always. When U design a small board, with short traces, and not to route any hi-speed signal to connectors, maybe you do not need any termination until 150-200MHz. There are working reference designs with 133MHz SDRAMs and without any termination.

Parallel (end) termination is rearly required, because it loads very strongly the logic outputs. 3,3V 60 Ohm load-> 55mA !!!

series termination not olways required, but not hurts. Rs=Z0-Rg (Rg=output imp.)

Added after 2 minutes:

striplines require a minimum of 6 layers! (routing: top, bott, inner2, inner3; planes: inner1, inner4)

 

[Rame]

Hi,

Go through books of eric bogatin & Douglas brooks,this will help you to have basic knowledge related to high speed.

Mr brooks as written several articles related to this topic,visit ultracad url,it is really cool site for beginners.


Regards

RAME