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Re: OpAmp design - from theory to practice

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On 30/03/2017 09:02, Francesco Zappon wrote:
> On Wednesday, 29 March 2017 18:53:21 UTC+2, Tim Wescott  wrote:
>
>> Just to _really_ throw a wrench into the works:
>> <whatever>-to-frequency is an old idea that's mostly gone out of
>> favor because of advances in digital processing and in ADC
>> converters.  If I were on your team I would be questioning the
>> system-level decision to continue using it -- but I'd be ready to
>> back off from that if there's good reasons to stick with it.

We used to do it that way to bodge an analogue only high range onto what 
was originally designed as an ion counting system using the existing 
backend which was similar to an HEP multichannel analyser. It didn't do 
the detector much good lifetime wise but it sold more kit.

> As I said, not an expert; I am not really sure what is the message
> you are trying to convey here, so I can give you some more details:
>
> - we are designing a custom ASIC because discrete components cannot
> withstand the expected level of radiation (target is 10kgy in 20
> years and probably more) - given that, we cannot use FPGAs either!
> the ASIC must operate "standalone" and using basic components only
> (all validated for radiation hardness, of course) - starting from
> this, I don't really see other solutions. I mean, maybe a
> self-switching, multi-range CFC might not be the best option
> (Sigma-Delta? pipeline?) but we have an input current and we need to
> digitize it, there is no escape from that :)
>
> Thanks also for the other answer, of course.

Can the device not be shielded with lead foil to some extent?

This although now very dated might give you some inspiration as a 
starting point for a suitable current to frequency design:

http://www.spelektroniikka.fi/kuvat/lm331b.pdf

> Since you are not the first person giving me that answer, I am
> starting to wonder if my question is simply a non-question, because I
> am still left with my doubts.
>
> Oh well, I'll keep studying I guess :)

Mass spectrometers Faraday cups often do a high gain stabilised current 
to voltage conversion and then digitise the resulting voltage. This 
leaves you with thermal drift, gain stability and zero level problems.

-- 
Regards,
Martin Brown

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OpAmp design - from theory to practice Francesco Zappon <cescozep@gmail.com> - 2017-03-29 07:55 -0700
  Re: OpAmp design - from theory to practice Tim Wescott <tim@seemywebsite.com> - 2017-03-29 11:51 -0500
  Re: OpAmp design - from theory to practice Tim Wescott <tim@seemywebsite.com> - 2017-03-29 11:53 -0500
    Re: OpAmp design - from theory to practice Francesco Zappon <cescozep@gmail.com> - 2017-03-30 01:02 -0700
      Re: OpAmp design - from theory to practice Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2017-03-30 10:54 +0100
        Re: OpAmp design - from theory to practice sroberts6328@gmail.com - 2017-03-30 05:25 -0700
      Re: OpAmp design - from theory to practice Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2017-03-30 14:37 +0200
        Re: OpAmp design - from theory to practice Francesco Zappon <cescozep@gmail.com> - 2017-03-30 07:16 -0700
          Re: OpAmp design - from theory to practice Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2017-03-30 20:25 +0200
            Re: OpAmp design - from theory to practice bitrex <bitrex@de.lete.earthlink.net> - 2017-03-30 14:51 -0400
            Re: OpAmp design - from theory to practice Joerg <news@analogconsultants.com> - 2017-03-30 12:58 -0700
              Re: OpAmp design - from theory to practice pcdhobbs@gmail.com - 2017-03-30 13:25 -0700
              Re: OpAmp design - from theory to practice Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> - 2017-03-30 23:55 +0200
                Re: OpAmp design - from theory to practice Joerg <news@analogconsultants.com> - 2017-03-30 16:43 -0700
          Re: OpAmp design - from theory to practice George Herold <gherold@teachspin.com> - 2017-03-30 11:43 -0700
            Re: OpAmp design - from theory to practice Francesco Zappon <cescozep@gmail.com> - 2017-03-30 15:02 -0700
            Re: OpAmp design - from theory to practice Jeroen Belleman <jeroen@nospam.please> - 2017-03-31 10:20 +0200
      Re: OpAmp design - from theory to practice Tim Wescott <tim@seemywebsite.com> - 2017-03-30 12:14 -0500
        Re: OpAmp design - from theory to practice Francesco Zappon <cescozep@gmail.com> - 2017-03-30 15:05 -0700
  Re: OpAmp design - from theory to practice Joerg <news@analogconsultants.com> - 2017-03-30 10:45 -0700
    Re: OpAmp design - from theory to practice JM <dontreplytothis173@gmail.com> - 2017-03-30 19:32 +0100
      Re: OpAmp design - from theory to practice Joerg <news@analogconsultants.com> - 2017-03-30 12:47 -0700
        Re: OpAmp design - from theory to practice Francesco Zappon <cescozep@gmail.com> - 2017-03-30 15:16 -0700
          Re: OpAmp design - from theory to practice George Herold <gherold@teachspin.com> - 2017-03-30 16:11 -0700
          Re: OpAmp design - from theory to practice Joerg <news@analogconsultants.com> - 2017-03-30 16:57 -0700

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