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Groups > sci.electronics.design > #454123 > unrolled thread
| Started by | Francesco Zappon <cescozep@gmail.com> |
|---|---|
| First post | 2017-03-29 07:55 -0700 |
| Last post | 2017-03-30 16:57 -0700 |
| Articles | 5 on this page of 25 — 11 participants |
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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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| From | JM <dontreplytothis173@gmail.com> |
|---|---|
| Date | 2017-03-30 19:32 +0100 |
| Message-ID | <objipn$8hb$1@dont-email.me> |
| In reply to | #454250 |
On 30/03/2017 18:45, Joerg wrote: > On 2017-03-29 07:55, Francesco Zappon wrote: >> Hello everyone, >> >> first post here. I hope I do not break any rule; let me know if this >> is the case. >> > > There are not many rules out here anymore :-) > > <ducking for cover now> > > >> Disclaimer: not native English speaker, forgive any mistake. >> > > Your English looks very good (I am non-native myself). > > >> My background: master degree in physics (with a few courses in >> electronics). PhD in electronics/physics, doing 99% of digital >> design. My last encounter with analog design: 10 years ago (ie: my >> knowledge is a bit "rusty"). >> >> The problem: I work in high energy physics. Currently, my new project >> is to design a new version (in a new technology: from 250nm to 130nm) > > > 130nm isn't considered very new these days but, of course, for radhard > your selection will be limited. New designs are still done in the larger > geometries. The most recent one I was involved in was 300nm. > > >> of a chip which has to perform current-to-frequency (CFC from now on) >> conversion. (for background information, if interested, you can read >> the previous designer work here: >> http://dx.doi.org/10.1016/j.mejo.2013.08.020 if you have access). >> > > Do you have a link where this paper can be accessed without charge? From > non-subscribers they want about $40 just to take a look. > > >> Basically, I need to design a CFC with input currents ranging from >> 1nA to 1mA, with a 40 us integration window and low input leakage >> (target: 100fA). Other details can be provided if needed. >> >> The main problem is the design of the amplifier. I am studying the >> common designs and the usual architectures; BUT I have a difficult >> time in connecting the high-level specification of the device (CFC, >> min/max input current, etc..) with the low level specs of the >> amplifier (a fully differential OTA, if we keep the previous >> architecture) such as GBP, phase margin, slew rate, etc... >> > > 1nA gets you into noise floor issues with the first stage if the > integration window means >20kHz bandwidth. > > >> I understand that there is no such thing as a "magical" formula to >> design such circuits, but I assume that there must be, somewhere, a >> point from where to start, which is what I am missing here. >> >> All the examples and designs I see (in tutorials or articles) start >> from the wanted specifications of the OpAmp, which would be good, if >> I had an idea on how to obtain them! >> >> I hope that the question make sense to you. >> >> Any help you can give is greatly appreciated! >> > > Usually the first stage needed would be a transimpedance amplifier or > TIA, in other words a glorified current to voltage converter, followed > by a V/F conversion or another more modern method. Phil Hobbs here in > this group is the guru on low noise TIAs, maybe he could chime in. > > It might also help to talk to these guys: > > http://ams.aeroflex.com/pagesproduct/datasheets/MilAero_ASIC_Brochure.pdf > https://www.dropbox.com/s/52nqfror1jhkqm0/venturini2013.pdf?dl=0
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| From | Joerg <news@analogconsultants.com> |
|---|---|
| Date | 2017-03-30 12:47 -0700 |
| Message-ID | <ek55mdFpc5U1@mid.individual.net> |
| In reply to | #454253 |
On 2017-03-30 11:32, JM wrote: > On 30/03/2017 18:45, Joerg wrote: >> On 2017-03-29 07:55, Francesco Zappon wrote: >>> Hello everyone, >>> >>> first post here. I hope I do not break any rule; let me know if this >>> is the case. >>> >> >> There are not many rules out here anymore :-) >> >> <ducking for cover now> >> >> >>> Disclaimer: not native English speaker, forgive any mistake. >>> >> >> Your English looks very good (I am non-native myself). >> >> >>> My background: master degree in physics (with a few courses in >>> electronics). PhD in electronics/physics, doing 99% of digital >>> design. My last encounter with analog design: 10 years ago (ie: my >>> knowledge is a bit "rusty"). >>> >>> The problem: I work in high energy physics. Currently, my new project >>> is to design a new version (in a new technology: from 250nm to 130nm) >> >> >> 130nm isn't considered very new these days but, of course, for radhard >> your selection will be limited. New designs are still done in the larger >> geometries. The most recent one I was involved in was 300nm. >> >> >>> of a chip which has to perform current-to-frequency (CFC from now on) >>> conversion. (for background information, if interested, you can read >>> the previous designer work here: >>> http://dx.doi.org/10.1016/j.mejo.2013.08.020 if you have access). >>> >> >> Do you have a link where this paper can be accessed without charge? From >> non-subscribers they want about $40 just to take a look. >> >> >>> Basically, I need to design a CFC with input currents ranging from >>> 1nA to 1mA, with a 40 us integration window and low input leakage >>> (target: 100fA). Other details can be provided if needed. >>> >>> The main problem is the design of the amplifier. I am studying the >>> common designs and the usual architectures; BUT I have a difficult >>> time in connecting the high-level specification of the device (CFC, >>> min/max input current, etc..) with the low level specs of the >>> amplifier (a fully differential OTA, if we keep the previous >>> architecture) such as GBP, phase margin, slew rate, etc... >>> >> >> 1nA gets you into noise floor issues with the first stage if the >> integration window means >20kHz bandwidth. >> >> >>> I understand that there is no such thing as a "magical" formula to >>> design such circuits, but I assume that there must be, somewhere, a >>> point from where to start, which is what I am missing here. >>> >>> All the examples and designs I see (in tutorials or articles) start >>> from the wanted specifications of the OpAmp, which would be good, if >>> I had an idea on how to obtain them! >>> >>> I hope that the question make sense to you. >>> >>> Any help you can give is greatly appreciated! >>> >> >> Usually the first stage needed would be a transimpedance amplifier or >> TIA, in other words a glorified current to voltage converter, followed >> by a V/F conversion or another more modern method. Phil Hobbs here in >> this group is the guru on low noise TIAs, maybe he could chime in. >> >> It might also help to talk to these guys: >> >> http://ams.aeroflex.com/pagesproduct/datasheets/MilAero_ASIC_Brochure.pdf >> > > 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). 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? 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 -- Regards, Joerg http://www.analogconsultants.com/
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| From | Francesco Zappon <cescozep@gmail.com> |
|---|---|
| Date | 2017-03-30 15:16 -0700 |
| Message-ID | <09b489fd-f376-4dbf-84ad-cf19263cfa41@googlegroups.com> |
| In reply to | #454264 |
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 (degrading the low current measurements) - the need of an FPGA to operate the chip (to control it and readout the data) - some linearity issues > > 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. 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. 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. > > 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! Francesco
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| From | George Herold <gherold@teachspin.com> |
|---|---|
| Date | 2017-03-30 16:11 -0700 |
| Message-ID | <682615f6-4126-4f2d-be91-6885cef6162d@googlegroups.com> |
| In reply to | #454290 |
On Thursday, March 30, 2017 at 6:17:04 PM UTC-4, 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 (degrading the low current measurements) > - the need of an FPGA to operate the chip (to control it and readout the data) > - some linearity issues > > > > > > 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. > > 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. > > 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. Hmm, I guess a lot depends on where the problems are. Are the caps in the silicon? (could they be external?) Radiation damage seems like it would cause leakage everywhere.. (~proportional to area.) George H. > > > > > > 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! > > Francesco
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| From | Joerg <news@analogconsultants.com> |
|---|---|
| Date | 2017-03-30 16:57 -0700 |
| Message-ID | <ek5karF3h7rU1@mid.individual.net> |
| In reply to | #454290 |
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/
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