Re: gEDA-user: C++ HDL

[John Doty <jpd@xxxxxxxxx>]

On May 15, 2009, at 2:06 PM, Joerg wrote:

> 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,

So will the 6L6, but few engineers ever have reason to design with one.

> 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

Doesn't have to be reasonable cost. The Amptek thing everybody uses  
is $250 apiece, and is too bulky and power hungry for something like  
an x-ray APD array. If NASA and DARPA ever quit arguing over who  
should fund XNAV, they have the need, and they have the money. But  
they're both as bad as Windows users: "We have a common interest so  
here's what I need you to develop for me for free...".

> 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 :-(

The handwriting is on the wall.

>
> [...]
>
> -- 
> Regards, Joerg
>
> http://www.analogconsultants.com/
>
>
>
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John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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