Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.electronics.design > #454299

Re: OpAmp design - from theory to practice

Show all headers | View raw

On 2017-03-30 15:16, Francesco Zappon wrote:
> On Thursday, 30 March 2017 21:47:29 UTC+2, Joerg  wrote:
>
>
>>> https://www.dropbox.com/s/52nqfror1jhkqm0/venturini2013.pdf?dl=0
>>
>>
>> Thanks! That helps a great deal. The SNR numbers in there do not
>> look very stellar but they claim to have achieved all objectives
>> stated (using sub-ranging though).
>
> Thanks JM for posting it before me!
>
> I was not directly involved with the project, but from the notes I
> found around it seems that the main "problems" they had with the
> first version (the one in the article) were: - too much leakage


Maybe you should then look into SOI like Phil suggested. Then guard 
rings and all the usual low-current tricks.


> (degrading the low current measurements) - the need of an FPGA to
> operate the chip (to control it and readout the data) - some
> linearity issues
>

Linearity will always be tough because of your 120dB. FPGA could be done 
in space. Work together with Gerhard maybe? He is located close to you 
and is self-employed as far as I know.

>
>>
>> Francesco, I am wondering what you'd like to improve above and
>> beyond what these guys did? Is it the sub-ranging and subsequent
>> SNR trade-off that you don't like?
>
> I don't know if I can really say I want to "improve" it. The chip
> itself was working quite nice, but for several reasons (I can
> explain, but it would take a long post and it is not super-relevant
> to the discussion here) we need a new version with a new technology.
>

If it is more or less a transfer from an obsolete technology to a new 
one for foundry reasons and such I'd talk to an analog IC design house.


> Now, I can keep the same approach (no problem on my side) but
> changing technology node means doing a redesign and re-dimension of
> the OTA, for starters. And this is where I struggle, because I am a
> bit in the dark about how to "obtain" the specs of the amplifier.
>

I can't imagine going to another node being a large obstacle. You can 
always use larger geometries as you did before, it's just the minimum 
that is now lower. Plus of course process differences but that is where 
a good IC design house helps. We always used those for IC designs, never 
went it alone.


> But I think I might be starting from the wrong point (after reading
> the posts here): I probably should start with the OpAmp as a black
> box and consider it ideal, and from there calculate the behavior of
> the circuit in ideal conditions; and after this, probably the OpAmp
> becomes a bit more straightforward.
>

Just keep in mind that in the real world nothing is ideal and you will 
always have offset, offset drift, offset tempco and such effects.

>>
>> If you really want to use a I/F concept (which as others have
>> hinted may not be the optimum here) there are V/F converters where
>> the manufacturer claims 6 decades which corresponds to 120dB:
>>
>> http://www.ti.com/lit/ds/symlink/vfc320.pdf
>>
>> This would have to be preceded by a low noise TIA for a current to
>> voltage conversion and those architectures are described in the
>> field of pre-biased photodiodes. Like here:
>>
>> http://electrooptical.net/www/frontends/frontends.pdf
>
> Thanks for all the info. I have some reading to do!
>

It sure is a nice engineering challenge. Those are the things that keep 
us young :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

Back to sci.electronics.design | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

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

csiph-web