How to make a super fast sampling head?

I've played with the 45 GHz SiGe bipolars, and always found them to be slow as time-domain amps or switches. And they love to oscillate in wideband circuits.

PHEMTS on the other hand are phenomenal. Today I was testing a cheap NEC part, NE3509M04. Gate capacitance measures under 0.8 pF, drain is about 0.35, Rds-on is about 6 ohms at zero gate voltage, and it switches on/off fast and clean with ecl-type gate swings. It has no equivalent of bipolar saturation delay; pull the gate to -0.4, and it just turns off.

The weird thing is that Rds-on has a negative TC. I've never seen a fet do that before.

(Used my trusty old green Boonton analog c-meter. The bottom meter range is 0 to 1 pF, and it has provision for offsetting strays, 2/4 terminal measurements, and dc bias injection.)

John

On a sunny day (Thu, 10 Jan 2008 14:21:32 -0800) it happened John Larkin wrote in :

Great, can afford 4 of those I think.

On a sunny day (Thu, 10 Jan 2008 22:39:15 GMT) it happened Joerg wrote in :

Found them in .nl, their wesite sucks though.

Got the pdf, needs some reading and getting used to very low inductances like .3 nH :-)

Hey, even a shotglass of Beerenburger with Friese Nagelkaas ist over four Euros these days ...

--
Regards, Joerg

http://www.analogconsultants.com/

I haven't tried the BFP620 yet, running other tests right now. So far my projects don't require more than the BFS17 or maybe the BFR93. But even

6GHz ft is probably considered a slowpoke in your world.

Thanks! Entered into my Dear Santa list.

I am using my dipmeter for small Cs. Sometimes the analyzer but that thing makes such a racket with its airflow.

--
Regards, Joerg

http://www.analogconsultants.com/

It seems complete and utter madness doing this stuff discretely in this day and age. You'll have more problems getting the signal into a fast ADC, without distortion.

So, how do you build a 50psec sampler non-discrete?

--
Regards, Joerg

http://www.analogconsultants.com/

The only thing I can say to counter your statement is that we do picosecond electronics discretely in this day and age, and charge lots of money for it. At the low to moderate quantity that specialized electronics is sold, and the cost/yield of custom GaAs and other exotic materials, discrete design is perfectly reasonable.

Surface-mount parts are so small and fast they have pretty much destroyed the hybrid business; the Tek 20-50 GHz sampling heads were hybrids. The "wall in the sky" for surface-mount design is at about

100 picoseconds, where things start to get tough.

The point of equivalent-time sampling is that the adc can be arbitrarily slow; the front-end acts as a picosecond-gate sample-and-hold.

Really, all you need is the Digikey catalog and ebay and some persistance to build good high-speed signal processing stuff.

John

In stock at Digikey.

John

The fastest samplers, well above 250 GHz by now, are custom GaAs parts. They use a nonlinear transmission line (shock line) to sharpen the edge from an external SRD, and integrate the sampling diodes at the end. Megabucks of engineering.

Agoston Agoston, of Hyperlabs and formerly Tek, did a 20 GHz sampler on FR-4 with surface mount parts, at least 10 years ago. It looks like any ordinary pc board.

Tek and HP sort of called a truce at about 70 GHz, probably because signals this fast berely go through coax or connectors. PSPL sells a

100 GHz shockline sampler, and I think maybe LeCroy has built a scope around it.

John

Your recommendation seems to have cleaned them out.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Nope, you guys must have cleaned them out.

--
Regards, Joerg

http://www.analogconsultants.com/

Ok, full custom it can be done, of course. But that's mega-bucks just in NRE before you even have anything on the bench.

--
Regards, Joerg

http://www.analogconsultants.com/

AFAIK even stuff like this is done on circuit board (but not FR-4):

I used to love hybrids, designed some of them. Active laser trim is a fantastic design tool, you can do things you wouldn't even dream about in regular design or chip design. But yeah, in the early 90's the bottom fell out of that business :-(

Plus one minor detail: Potential customers with enough budget.

--
Regards, Joerg

http://www.analogconsultants.com/

Tell me about it - though my 500psec sampling head was stroboscopic electron microscope, which sold for about $100,000 dollars before we added our timing and data-collecting electronics.

-- Bill Sloman, Nijmegen

TriQuint Semiconductor has a Prototype Chip Option program where they sell you a place on a shared Mask Set for a lot of their PHEMT & HBT processes. You get a small amount of chips for a smaller price with the shared Mask running at regular intervals. The details, and prices, are listed here.

There's also a larger shared Mask program, called the Prototype Development Quickturn, PDQ, listed on another page.

I don't see their new combined HBT and PHEMT process, TQBiHEMT, listed on the prototype schedule but it's possible the Web page hasn't caught up yet.

Robert H.

Cool. What we want is...

4 3 | | +---+ | d +--g | s | | +---+-----+----5 | | | | d d 1----g-----g s s | | | | +-----+ | | | | 2 6

which looks a lot like an old GigaBit Logic depletion-load logic gate. It works pretty well with the NEC parts, but integrated it would really scream.

John

It may be worthwhile to you at those prices (bottom of the page). You'd know better than me. But unless you're talking about larger FETs the part will probably be dominated by the bond pads. You might be able to find someone that can bond you up some die using less than standard size bond pads to get more on an order.

There are free tools around to lay it out. TriQuint used to supply free layout Libraries for IC Editor's ICED layout tools (Layout, DRC, LVS). I saw from their web site recently that they've gone to open source and have a free download.

TriQuint would be able to tell you about what tools their Library supports. I used to layout customer designs in ICED and for your circuit all you'd need to do would be to streach their standard FETs to the size you'd need.

Robert H.

I should mention that they used to supply all their device Models for PSpice as well. You'd have to model the strays yourself but they had some guidance. Or used to.

Robert H.