Lost a Bet

Nifty. Can you take a shot of the whole trace, including the SMA at the far end?

-- john, KE5FX

Corollary to that: coupling between adjacent microstrip is s***ty. Good news for parallel buses, bad news* for differential traces.

The drool means it's pretty bad for certain RF purposes (say, filters and matching networks?), and longer analog delays (maybe with some compensation though?). When you don't care about any of that because your logic thresholds are 30-70%, it's no problem.

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

The TDR includes the whole trace, up to about cm 9. The losses in the traces blur the TDR resolution such that the end SMA doesn't show up much. TDR is only approximately a graph of impedance vs distance; losses mess things up.

I should have done another TDR starting at the other end. I'll do that.

With 16 mil traces and 6 mil spaces on 9 mil dielectric, coupling is small.

The step response is fine for logic. It is a pretty long trace.

What Phil said, and also, stripline can be made with much more beneficial geometry -- face-to-face rather than side-by-side, for example.

There's also lots more stackups than a standard 4 layer build: a pair of 30 mil traces, on 62 mil core, with 7 mil separation (a standard 2-layer board), are coupled more closely than a pair of 10 mil traces, 7 mil separation, 10 mil prepreg (standard 4-layer board).

Or, for the 4-layer build, simply removing the ground plane beneath the trace, so you get a half trench stripline geometry.

You could even make a slotline geometry with even higher coupling (but also fairly high impedance, unless you use a high-k substrate).

I think it would be difficult to make wideband (>> 1 octave) directional couplers over, say, -20dB, in microstrip.

Tim

Here's the TDR starting from the tight meander end. Again, the opposite SMA connector (at the right-most cursor dot) is blurred by the trace losses.

The vias are less distinct, too.

Well I hope your colleague is extremely patient, 'cos I'm still waiting for the burger & fries you owe me from our wager back in 1998!!

Isn't there a statute of limitations on newsgroup bets?

What was that about anyhow?

Yes. 6 years. After that it's only binding in honour only.

F***ed if I can remember after all this time, John. But I do recall my prize was a burger & fries and a beer in a biker bar somewhere dangerous (Oakland, in all probability). Oh - and I of course regard you as a highly honourable man.

Well, we could go to Zeitgeist. It's a biker bar, but the kind of bikes with pedals. 44 beers on tap. Al fresco dining, sticky picnic tables under a freeway ramp. Joerg loved it. Free matches.

The food is actually good. Burgers, home fries, grilled cheese sandwiches.

"Warm beer, cold women"????? N..i..c..e! Since you're picking up the tab, I shall require something a bit more classy (well, classy for Oakland, anyway:)). Somewhere not totally burnt- out, for example. It's not too much to ask after a 19 year wait, surely?

Oakland? I don't know much about Oakland, except that it's generally dangerous.

My not-yet-then-wife used to live in Oakland. I decided that the world's biggest impedimet to romance is the Bay Bridge. So, she moved.

Zuni and Absinthe both have high-end burgers, $16 ballpark and worth it. Trick Dog is amazing, both the burger (long and skinny, on a hot dog bun) and the fries (hot and gooey inside, crispy as broken glass on the outside.) Dang, I'm hungry.

That's all part of the appeal, though, don't you think? I mean, that's why we decided to meet up in a biker-bar honky-tonk burger-joint there. Have you lost your sense of adventure?

Very sensible. All that fog and whatnot. No good.

After a near 20 year wait, so am I! :P