John Doty wrote: > On May 12, 2009, at 12:38 AM, Stephan Boettcher wrote: > >> Joerg <[email protected]> writes: >> >>>>> The topper was a professor at my university who said that soon >>>>> everything will be ICs, that transistors and most of that discrete >>>>> stuff would go away. I burst into laughter in the auditorium, a bit >>>>> embarrassing ... >>>> Well, in case you haven't noticed, it's headed that way. My CCD >>>> measurement chains of 10-20 years ago were full of discrete >>>> transistors. IC's were not up to the job at the power levels >>>> required >>>> for a space instrument. Present day versions have no discretes, but >>>> use less power, and are faster and quieter. It's physics: the >>>> scaling >>>> laws tell you that in most cases, smaller transistors with shorter >>>> interconnections are better. You can only go so far down this road >>>> with discretes. Still need a big power transistor? Those are mostly >>>> IC's, too: millions of tiny transistors in parallel. >> Our charge sensitive preamps for the Radiation Assessment Detector >> (RAD) >> on the Mars Science Lab mission (launch 2011) use a discrete input >> FET. >> 17 bit dynamic range are still tough in an integrated circuit, when >> the >> noise level is supposed to be 1000 electrons, and the largest expected >> signal is 150M electrons. The problem is less with the power, but >> mass. >> 1cm² board space per preamp is significant weight, if it needs to >> go to >> Mars. Even more expensive was the paperwork to get that FET (BF862) >> qualified. >> > > Yep. A couple of years ago, the MIT folks I work with were doing some > experiments with x-ray detection using APDs. The system I designed > for them used a BF862 at the front end. But how much longer will this > last. The process folks keep improving their ability to mix > technologies. I think somebody will come up with a process mixing low > voltage JFETs with bipolar, some designer (maybe even you or me) will > then put a preamp (or maybe a whole measurement chain) in a six bump > BGA, and this part of the discrete game will be over. It's had an > awfully long run though: the Amptek hybrid that is the "industry > standard" here is a slight modification of a preamp my old MIT > colleague Bob Goeke designed in the early 1970's. I have a copy of > the original schematic around here somewhere... >
I think the BF862 will be around for a long time, else Digikey wouldn't keep >10k of them in stock most of the time. The six bump BGA (I hate BGAs...) won't ever happen at reasonable cost unless there is a huge consumer app that needs it. Some laser measurement device or whatever. As for smaller geometry JFETs, those unfortunately do tend to vanish and someday we might even read a eulogy on ye olde 2SK3372 :-( [...] -- Regards, Joerg http://www.analogconsultants.com/ _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
