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horrible, horrible

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I'm doing this layout myself, which is easier than trying to explain all the constraints to someone else. But it's still horrible. I think I've just past the point of maximum chaos.

It could have been 4 layers, but the power pours and bypassing would be a nightmare, so I'll go for 6. So two ground planes, two power planes, two signal layers, for stack symmetry. On this fast stuff, all the important traces are on layer 1; vias are deadly below 100 ps.

The cryptic notes on the right are trace width reminders for 50 and

100 ohm microstrip on the outer layers. We had been including a nice chart on most boards, but then the board houses come back with a zillion questions about impedance control, even when we have a big HIGHLAND NOTES ONLY thing.

U22 is a $330 distributed amplifier. Maybe the 100 piece price is better.

(Sorry to interrupt the politics and viruses and squabbling with electronics.)

Reply to
jlarkin
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You are forgiven. ;-)

Jeroen belleman

Reply to
Jeroen Belleman

Finding U22 was fun kinda like Where's Waldo. Oh there he is.

Reply to
bitrex

Indeed "rather than explaining all the constraints to someone else" In other words, PCB layout requires high degree of specialized skills. I used to do layout on PADS but simple, audio stuff, not like this. Nevertheless, I saw the benefit of a mind that can think multi-dimensionally. That requires high intelligent, especially visualization.

John, If the project is similar to or based on another, can it take advantage of layout already done for the parent project? Can modular design apply here?

cheers, Rich S

Reply to
Rich S

My understanding is that power layers are just as good as ground for impedance control. So why two ground layers? What will the stack up be?

Reply to
Rick C

I can't really explain all the constraints to someone else; I sort of just feel it. And I can change the schematic when it helps the layout.

Doing this myself has moments of gotcha, makes me think about stuff I may be doing wrong.

The distributed amp has a gbw around 140 GHz. The nearby MMIC is about the same. The composite gain-bandwidth is about 2e22.

This is pretty much new, but the output stage layout, the distributed amp and the monitor buffer MMIC, can be reused on another board in the same box.

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Those sideways 0306 caps are cool, but you can't run a 50 ohm trace into them. The trace end radius shorts out the cap. So I have to run skinny traces and then pave them over with rectangular copper pours. Nuisance.

L9 is a Coilcraft 6 GHz inductor, sort of a more sensible version of the awful conical things. But a soleniod inductor has two components, the obvious inductance and the impedance of the wire viewed as a transmission line. So the TDR has a little flat spot before the L/R curve kicks in.

Reply to
John Larkin

mandag den 20. september 2021 kl. 23.23.24 UTC+2 skrev John Larkin:

can't just end the fat trace early and add skinny trace to keep DRC happy?

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highlighted skinny trace from end of fat trace to center of pad

Reply to
Lasse Langwadt Christensen

That leaves the two little hickies. We can't have that!

Reply to
John Larkin

tirsdag den 21. september 2021 kl. 01.00.29 UTC+2 skrev John Larkin:

make a special footprint with extended pads and only parts of it in mask/paste layer

Reply to
Lasse Langwadt Christensen

Buried stripline is less dispersive than microstrip on the surface of the board.

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The Rogers "experts" didn't mention that. If you really want 100psec rise-times at the end of your transmission lines, it might pay to bury a strip-line or two.

You can't afford a via anywhere along the track, but the source and destination are unavoidable discontinuities anyway.

If you want tighter control of the impedances, sandwiching buried stripline between layers of a low dielectric constant substrate lets you get away with wider lines.

Of course better quality electronics would be even better.

Reply to
Anthony William Sloman

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