RF coupling with multiple capacitors

Nov 15, 2005 34 Replies

I remember reading it--that was the Dana Labs Digiphase. They really did make it work, eventually, and sold a few but then the company went down the tubes....

My situation wasn't quite that bad, thank heavens--I did get it to work with a funky decimal rate-multiplier driven pulse swallowing counter.

The nasty rate-multiplier jitter is much less of a problem when it's in the lowest decades of the counter that runs the pulse-swallowing line. In this case, two cascaded CD4527 rate multipliers drove the carry input of a 74LS190 presettable down counter, which drove the modulus control of a Motorola 10/11 ECL prescaler whose number I forget.

Worked great, eventually--you could set the 14 GHz oscillator frequency directly on BCD dip switches and everything. I sure wasn't going to make that 1/f noise spec with an 8.333 kHz comparison frequency--the FM noise would have multiplied up by 124 dB.

I know a few stories like that Dana Labs one, which is one of the reasons I wanted to work for IBM Research--they pay me to go play in my laboratory, and have done for 18 years now. (Please, nobody here wise them up.) ;-)

Management commitment that will survive failure is rare and precious.

Cheers,

Phil Hobbs

Why should it? They are both the same l/w ration, so I'd expect ESL to be about the same, just under a nH. If the capacitor is used for RF interstage coupling, it's part of a transmission line and its ESL is probably about the same as the length of transmission line it replaces.

Jeroen Belleman

Yes please, that'd be interesting. But could you put in a corner of a web site please? I have no a.b.s.e. here.

Thanks, Jeroen Belleman

Well, by that argument, a 1206 should have the same ESL too, right? And I'm pretty sure most people would agree that a 1206 has a measurably greater ESL than an 0402. I do see your point though; I can readily imagine that 0603 and

0402 are starting to get close enough in size that their ESLs differ by less than the measurement certainty...

For a single layer capacitor that's roughly the same width as the transmission line it replaces, I'd agree with you. For a multi-layer capacitor, however, I submit that it can be noticeably (e.g. 4x) less.

Thanks for the input,

---Joel

Thanks John, great pictures.

Dana 7030, as seen at

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newell

And now you can do most of that on a few square inches of pcb with a $5 DDS chip.

John

If you have the $750 loose, buy it. A genuine piece of engineering history.

Cheers,

Phil Hobbs

Try this:

ftp://ftp.highlandtechnology.com/tee.zip

John

Space is tight in the museum these days, so I'll pass. It doesn't look at all like I'd mentally pictured it from the description in "Analog Circuit Design".

I wish Jim Williams would put out another analog storybook. I'll bet that you, Larkin, and Thompson (among others here) could come up with some good material (hint, hint).

newell

Well, I don't know if we could top the one with the dog holding the soldering iron...

But I did publish a war story of a somewhat similar kind, a couple of years ago in the Optical Society of America's house organ:

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(This web site is going to go away soonish, but it'll still be available via my redirector,
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I've been trying to get some of my electrooptical colleagues to do write similar pieces, but to little avail.

Cheers,

Phil Hobbs

On Fri, 18 Nov 2005 12:17:52 -0500, Phil Hobbs wrote: ...

Holy crap! "fluorinated Saran Wrap?" KEWL!!! %-}

Cheers! Rich

Awwww. It sounds like a really great idea. Sigh.

Is anybody doing the purse-light yet?

Thanks, Rich

Yes indeed. About 1nH. And a measurement using that nice HP8753D here confirmed that nicely.

Jeroen Belleman

Splendid. Instructive too. There's more to bias tees than meets the eye, clearly.

Thanks, Jeroen Belleman

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