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Microstrip wideband AC coupling

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0306 cap, capacitive bump. 0603 cap, inductive bump. No surprise that the 0204 is best. In the 25 ps sort of domain, on FR4, there's no need to buy exotic caps.

That 0204 is a 0.47 uF 16 volt cap. With 9 volts DC bias from my distributed amplifier, it loses 80% of its capacitance.

Reply to
John Larkin
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Comes up 500 at the moment.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Strange; that link used to work.

Dropbox used to just work. They have fancied it up and mostly broke it.

Reply to
John Larkin

Where do you find these sideways capacitors ?

Reply to
boB

Digikey. Search on "0204 capacitor" and 98 part numbers come up, including this one:

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0.47 uF, 4V, with most of the capacitance remaining at the rated voltage, 3 cents in reels.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Dropbox found the picture again. It does look like the 0204 is a good fit to the 50-ohm line. Do you have the TDRs handy?

Thanks

Phil Hobbs

Reply to
Phil Hobbs

How wide a 50 Ohm line is depends on eps-r of the board and the stackup. We got excellent results for the eye diagrams @ 10 GBps with 0402 AVX capacitors > 10 years ago.

And I wonder why the CV product is so much worse for the short & fat capacitors vs. the normal slim & long ones.

I have a lot of 0612 10u 6V3 here, DK 445-4072-1-ND, never used them.

cheers, Gerhard

Reply to
Gerhard Hoffmann

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The caps are at cm 7 in the upper/TDR trace. The Mueller edge-launch SMA connectors are worse than the caps. We did nail 50 ohms pretty good on this one.

Reply to
John Larkin

Very nice!

Cheers

Phil Hobbs

Reply to
Phil Hobbs

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