How do I measure the correct length for meander tool

[thomasstoll]

I found the longest signal with the "run length-freq-ri" ULP, it is 49mm. Now I select the Meander tool and enter 49mm in the command line. Now I select and meander the signal, when it reaches 100% the signal is much to long. What am I doing wrong, why is the length in the meander tool not the same as in "run length-freq-ri"? I can only find the correct length with try and fail. This takes to long and is unnerving. Is there a better way?

[mtl_asm]

Hi, can you try this:

Note the signal/net that is 49mm from the ulp.

Now click Meander and click on the signal from above (do not explicitly tell meander the 49mm on command line).

When you click a small box with a measurement in it will appear. Does the box that appears on the trace also say 49mm?

If it is not 49mm then whatever shows up on that click is what the meander tool thinks the signal length is

maybe a screen cap would help too. 

[jorge_garcia]

Hi @thomasstoll ,

The meander tool only measure the length of traces between to pads or two vias. It will not look at the full length of a net in the same way the ULP sums up all the traces in a net. Remember that one of the objectives involved length matching is to also match impedance once vias get involved that becomes much more difficult, the meander command looks at length between pads and vias. We recognize that the differential pair and meander tools need some work to make them more friendly but once you are aware of this, it easy to figure out why the numbers are sometimes different.

Follow @mtl_asm advice and equalize to the number given by the meander command, if you have a lot of layer transitions(not a good idea) then you will have to be much more careful. A screen cap would be helpful.

Best Regards,

[mtl_asm]

@jorge_garcia wrote:

The meander tool only measure the length of traces between to pads or two vias.

From my experience it ignores vias, IE it will not return the length of the segment between 2 vias as you mention here. (I'm on windows with v 9.4.2.). It will return the measure of a segment between 2 pads though.  Here are 2 screen caps at the same zoom, i think you will agree it is not returning the length of segment between 2 vias.

First here is the length of a segment between 2 pads. It says 21.5mm which is correct. 

Now if i go over to some short segment between 2 vias it says that short segment is 76mm but look how short it is compared to the 21.5mm ;). 

So it seems at least in 9.4.2 it does not care about vias much.

[jorge_garcia]

Hi @mtl_asm,

Thank you for the correction, you are right. I was going of off memory and I should have verified it. Thank you.

Ok so it is just between pads that it measures. So @thomasstoll , if you look at the first image @mtl_asm you'll see the difference between what meander measures and what the length-freq-ri.ulp will give. The meander command will only measure between the two pads, but the ULP will give you the total length of that net with all the other connections between pads made on that net.

Thanks again @mtl_asm.

Best Regards,

[thomasstoll]

Is there an ULP that gives me only the length between the pads, so I can find the longest track?

[mtl_asm]

maybe, but i don't know it off the top of my head.

you can do it with the meander tool somewhat already. its not as automated but you can do it by clicking the meander tool, then hold control and shift and click each of the segments in question. the goal length will become whatever the longest trace control clicked. 

for example here i have control shift left clicked this section of N$19 first, it shows length is 3mm, meander goal also 3mm. 

Now i control shift left click this much longer net "MIXER_5_B" and it shows 26.7mm. and now if you click back on that segment ofN$19 it should show the completion of  12% of 3mm and goal of 26.7mm. Whatever the greatest length that was control-shift-left clicked should be the goal.

so it is not a ULP but you can actually get the greatest length straight from using the meander tool and using control shift click.