Re: gEDA-user: C++ HDL

[Joerg <joergsch@xxxxxxxxxxxxxxxxxxxxx>]

John Doty wrote:
> On May 12, 2009, at 12:38 AM, Stephan Boettcher wrote:
> 
>> Joerg <joergsch@xxxxxxxxxxxxxxxxxxxxx> 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/



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