Re: Question on the "super gain" op-amp
From: Fred Bartoli (fred._canxxxel_this_bartoli_at_RemoveThatAlso_free.fr_AndThisToo)
Date: 08/26/04
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Date: Thu, 26 Aug 2004 18:49:06 +0200
"Winfield Hill" <Winfield_member@newsguy.com> a écrit dans le message de
news:cgkrl301utb@drn.newsguy.com...
> Fred Bartoli wrote...
> >
> >>| But you should carefully consider the reasonableness of your spec:
> >>| 0.002 ohms at 100kHz implies a total circuit series inductance of
> >>| under 3nH, which is clearly impossible or highly impractical.
> >>
> >> nice that is reached after 3 mm wire ;-)
> >
> > Well, I could achieve that for a 1.2m(eter) power cable, including
cables
> > connectors (heavy duty, "zero force", fast lock) to the backplane PCB,
2mm
> > connectors from the backplane to the PCB boards, main boards PCB, and
> > loadboard PCB.
> >
> > Lots of interdigitated connector pins, paralleled specially made coax.
> > cables and customized connectors.
>
> Fred, I can believe 0.002 ohms dc resistance, but sorry, not 3nH.
>
I know, it's amazing but you really should. It wasn't 2mR, maybe 5mR, but we
measured the 3nH, well, maybe 3.5nH.
We had a custom designed coax cable with ultra thin kapton isolation. Don't
remember it's loop inductance but I still have a sample in my office and
I'll measure it when I have time.
20 paralleled coaxs with custom made connector terminations (the coax where
wired on the connectors with an interdigitated pattern).
Someting like this :
F R F R F
R F R F R
F R F R F
R F R F R
(F = forward path, R = return path)
The 2mm connectors (from main PCB to the backplane) had almost 100 pins
(2x50) wired in a same pattern. The PCBs were of course designed
accordingly.
This inductance *had* to be pretty low : it was for a power supply I
designed in an ATE tester for testing the P4 (I guess it was this one) on
wafer (production and charaterization).
They wanted 200A sustained current, 100A current step capability, and IIRC
100A/ns (or was it 50A/ns ?) right at the wafer connections.
This was translated to about a small 1A/ns that the supply had to provide. I
designed the PSU for 7nH cable max, targetted the cable at 4nH and obtained
3.5.
This is about a 4V drop and is what was observed, confirming the cable
measurements.
A nice piece of work (and a huge amount of $) was what they call the "space
transformer", which supported more than a thousand springs to make contact
with the die bumps. It's a pyramid shape ***multi***layered ceramic device
with a lot of interdigitated vias whose purpose is to convert the external
world pin spacing to the die level spacing (springs). I don't know if I'm
clear.
The model I was given stated a few 10s of pH (yes pH) serial inductances.
-- Thanks, Fred.
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