Amplifier design pre-consultation consultation
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Posted by on July 3, 2008, 1:43 pm
Please log in for more thread options I'm a research scientists with the Johns Hopkins University, and I'm working on a set of designs for an X-ray detector, and trying to spec out various methods for obtaining the data we need. One of the designs is a system based on diode arrays + amplifiers + ADC system. I've already got a good handle on the detector end, and the data acquisition system, but I'm stuck on the amplifier system. We've used commercial amplifiers in the past, but they would likely be overkill for our situation, and end up quite pricey on a cost/channel basis. Given our specifications, I'm wondering if the optimal solution would be to pay for a consultant to develop and test a design specifically for our application, and then take that design and punch out the number of boards that we would need. Our generic needs seem to be fairly modest, 100-250kHz bandwidth with a gain of 10^7, but as always the devil is in the details. Naturally, we want the lowest noise possible so that we can measure signals at the nA or sub-nA level. So, here's the question. Are the specifications and schematic sketch shown here: http://picasaweb.google.com/ktritz/PhotodiodeAmplifierDesign/photo#5218836415390875906 adequate for a professional to provide a consultation estimate? Would the amplifiers be simple enough that a 2nd year EE student could manage the design, or are we talking about skirting the bleeding edge? I'm never contracted a consultant before, so should I expect a consulting price tag of $1000? $10000? I'm working with a budget that's higher than a hobbyist, but not quite corporation level. I would also be happy to discuss specific amplifier design ideas. Given the capacitance of the detectors in question, I would imagine that a very low voltage noise opamp is the way to go, or perhaps a JFET front end. The BF862 looks pretty good, and it's relatively high capacitance wouldn't matter much compared to the diode. Thanks, Kevin | |||||||||||||
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Posted by Tim Shoppa on July 3, 2008, 4:09 pm
Please log in for more thread options You don't say what part of Johns Hopkins you work at, but go talk to the particle and nuclear experimental physicists. Diode detectors followed by amps followed by A/D and triggers are their bread and butter. Google "silicon strip detectors" and find somebody who has worked in it more recently than me (1980's!). Tim. | |||||||||||||
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Posted by Kevin on July 3, 2008, 4:43 pm
Please log in for more thread options > On Jul 3, 1:43=A0pm, ktr...@gmail.com wrote:
> > > > > Greetings!
>
> > I'm a research scientists with the Johns Hopkins University, and I'm
> > working on a set of designs for an X-ray detector, and trying to spec > > out various methods for obtaining the data we need. One of the designs > > is a system based on diode arrays + amplifiers + ADC system. I've > > already got a good handle on the detector end, and the data > > acquisition system, but I'm stuck on the amplifier system. >
> > We've used commercial amplifiers in the past, but they would likely be
> > overkill for our situation, and end up quite pricey on a cost/channel > > basis. Given our specifications, I'm wondering if the optimal solution > > would be to pay for a consultant to develop and test a design > > specifically for our application, and then take that design and punch > > out the number of boards that we would need. >
> > Our generic needs seem to be fairly modest, 100-250kHz bandwidth with
> > a gain of 10^7, but as always the devil is in the details. Naturally, > > we want the lowest noise possible so that we can measure signals at > > the nA or sub-nA level. >
> > So, here's the question. Are the specifications and schematic sketch
> > shown here: >
> >http://picasaweb.google.com/ktritz/PhotodiodeAmplifierDesign/photo#52...
>
> > adequate for a professional to provide a consultation estimate? Would
> > the amplifiers be simple enough that a 2nd year EE student could > > manage the design, or are we talking about skirting the bleeding edge? >
> > I'm never contracted a consultant before, so should I expect a
> > consulting price tag of $1000? $10000? I'm working with a budget > > that's higher than a hobbyist, but not quite corporation level. >
> > I would also be happy to discuss specific amplifier design ideas.
> > Given the capacitance of the detectors in question, I would imagine > > that a very low voltage noise opamp is the way to go, or perhaps a > > JFET front end. The BF862 looks pretty good, and it's relatively high > > capacitance wouldn't matter much compared to the diode. >
> You don't say what part of Johns Hopkins you work at, but go talk to > the particle and nuclear experimental physicists. Diode detectors > followed by amps followed by A/D and triggers are their bread and > butter. Google "silicon strip detectors" and find somebody who has > worked in it more recently than me (1980's!). > > Tim. That certainly is a good suggestion, though often their designs are more suited to high speed pulse shaping/counting. Also, I'm actually located offsite at the Princeton Plasma Physics Laboratory, though I do have a few colleagues on campus that might be able to point me in the right direction. Another option is the Applied Physics Lab, but I have a feeling that unless you have an actual collaboration with them, getting their engineers involved is a 10k or higher proposition. My budget might be a bit constrained compared to what they are used to. Kevin | |||||||||||||
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Posted by Tim Shoppa on July 5, 2008, 7:53 am
Please log in for more thread options Kevin wrote:
> > On Jul 3, 1:43**pm, ktr...@gmail.com wrote:
> > > > > > > > > Greetings!
> >
> > > I'm a research scientists with the Johns Hopkins University, and I'm
> > > working on a set of designs for an X-ray detector, and trying to spec > > > out various methods for obtaining the data we need. One of the designs > > > is a system based on diode arrays + amplifiers + ADC system. I've > > > already got a good handle on the detector end, and the data > > > acquisition system, but I'm stuck on the amplifier system. > >
> > > We've used commercial amplifiers in the past, but they would likely be
> > > overkill for our situation, and end up quite pricey on a cost/channel > > > basis. Given our specifications, I'm wondering if the optimal solution > > > would be to pay for a consultant to develop and test a design > > > specifically for our application, and then take that design and punch > > > out the number of boards that we would need. > >
> > > Our generic needs seem to be fairly modest, 100-250kHz bandwidth with
> > > a gain of 10^7, but as always the devil is in the details. Naturally, > > > we want the lowest noise possible so that we can measure signals at > > > the nA or sub-nA level. > >
> > > So, here's the question. Are the specifications and schematic sketch
> > > shown here: > >
> > >http://picasaweb.google.com/ktritz/PhotodiodeAmplifierDesign/photo#52...
> >
> > > adequate for a professional to provide a consultation estimate? Would
> > > the amplifiers be simple enough that a 2nd year EE student could > > > manage the design, or are we talking about skirting the bleeding edge? > >
> > > I'm never contracted a consultant before, so should I expect a
> > > consulting price tag of $1000? $10000? I'm working with a budget > > > that's higher than a hobbyist, but not quite corporation level. > >
> > > I would also be happy to discuss specific amplifier design ideas.
> > > Given the capacitance of the detectors in question, I would imagine > > > that a very low voltage noise opamp is the way to go, or perhaps a > > > JFET front end. The BF862 looks pretty good, and it's relatively high > > > capacitance wouldn't matter much compared to the diode. > >
> > You don't say what part of Johns Hopkins you work at, but go talk to > > the particle and nuclear experimental physicists. Diode detectors > > followed by amps followed by A/D and triggers are their bread and > > butter. Google "silicon strip detectors" and find somebody who has > > worked in it more recently than me (1980's!). > > > > Tim. >
> That certainly is a good suggestion, though often their designs are > more > suited to high speed pulse shaping/counting. Also, I'm actually > located > offsite at the Princeton Plasma Physics Laboratory, though I do have > a few colleagues on campus that might be able to point me in the > right direction. > > Another option is the Applied Physics Lab, but I have a feeling that > unless > you have an actual collaboration with them, getting their engineers > involved > is a 10k or higher proposition. My budget might be a bit constrained > compared > to what they are used to. Kevin - Having looked at other requirements you've mentioned (Vacuum compatibility, cabling, noise) you don't need just an EE to design a pre-amp for you. At the rate I see requirements appearing, your proposed scheme with all its cabling will make the preamp engineering and construction costs less than 1 percent of the total price of instrumentation. Most of your cost is going to go into cables and connectors! You need someone with broader experience in experimental design, construction, integration, and data acquisition. An EE could certainly be part of this team, but it would be one with experience in integrating such experiments into your particular environmental requirements. When I was in the strip detector business, the preamps were mounted at the detector, and then there were massive bundles of differentially driven twisted pairs in ribbon cables ("Twist-N-Flat") running hundreds of feet to the big electronics. This was pretty "hot stuff" and in fact the trigger and A/D converters were massive racks cooled by chilled water. (Now, I also know chilled water is also something common to plasma experiment cooling!) But that was being done with essentially late 70's technology - electronics had evolved rapidly over the 80's and far more integrated solutions were coming available. By the early 90's, designs had realized that all that cabling wasn't optimal - instead integrated solutions with preamp, trigger, A/D all mounted within inches of the detector were being done. Again, google "silicon strip detector" to see the compromises and solutions. Tim. | |||||||||||||
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Posted by Joerg on July 5, 2008, 3:42 pm
Please log in for more thread options Tim Shoppa wrote:
> Kevin wrote:
>>> On Jul 3, 1:43**pm, ktr...@gmail.com wrote:
>>> >>> >>> >>>> Greetings! >>>> I'm a research scientists with the Johns Hopkins University, and I'm >>>> working on a set of designs for an X-ray detector, and trying to spec >>>> out various methods for obtaining the data we need. One of the designs >>>> is a system based on diode arrays + amplifiers + ADC system. I've >>>> already got a good handle on the detector end, and the data >>>> acquisition system, but I'm stuck on the amplifier system. >>>> We've used commercial amplifiers in the past, but they would likely be >>>> overkill for our situation, and end up quite pricey on a cost/channel >>>> basis. Given our specifications, I'm wondering if the optimal solution >>>> would be to pay for a consultant to develop and test a design >>>> specifically for our application, and then take that design and punch >>>> out the number of boards that we would need. >>>> Our generic needs seem to be fairly modest, 100-250kHz bandwidth with >>>> a gain of 10^7, but as always the devil is in the details. Naturally, >>>> we want the lowest noise possible so that we can measure signals at >>>> the nA or sub-nA level. >>>> So, here's the question. Are the specifications and schematic sketch >>>> shown here: >>>> http://picasaweb.google.com/ktritz/PhotodiodeAmplifierDesign/photo#52... >>>> adequate for a professional to provide a consultation estimate? Would >>>> the amplifiers be simple enough that a 2nd year EE student could >>>> manage the design, or are we talking about skirting the bleeding edge? >>>> I'm never contracted a consultant before, so should I expect a >>>> consulting price tag of $1000? $10000? I'm working with a budget >>>> that's higher than a hobbyist, but not quite corporation level. >>>> I would also be happy to discuss specific amplifier design ideas. >>>> Given the capacitance of the detectors in question, I would imagine >>>> that a very low voltage noise opamp is the way to go, or perhaps a >>>> JFET front end. The BF862 looks pretty good, and it's relatively high >>>> capacitance wouldn't matter much compared to the diode. >>> You don't say what part of Johns Hopkins you work at, but go talk to >>> the particle and nuclear experimental physicists. Diode detectors >>> followed by amps followed by A/D and triggers are their bread and >>> butter. Google "silicon strip detectors" and find somebody who has >>> worked in it more recently than me (1980's!). >>> >>> Tim. >> That certainly is a good suggestion, though often their designs are
>> more >> suited to high speed pulse shaping/counting. Also, I'm actually >> located >> offsite at the Princeton Plasma Physics Laboratory, though I do have >> a few colleagues on campus that might be able to point me in the >> right direction. >> >> Another option is the Applied Physics Lab, but I have a feeling that >> unless >> you have an actual collaboration with them, getting their engineers >> involved >> is a 10k or higher proposition. My budget might be a bit constrained >> compared >> to what they are used to. >
> Kevin - > > Having looked at other requirements you've mentioned (Vacuum > compatibility, cabling, noise) you don't need just an EE to design a > pre-amp for you. At the rate I see requirements appearing, your > proposed scheme with all its cabling will make the preamp engineering > and construction costs less than 1 percent of the total price of > instrumentation. Most of your cost is going to go into cables and > connectors! > > You need someone with broader experience in experimental design, > construction, integration, and data acquisition. An EE could certainly > be part of this team, but it would be one with experience in > integrating such experiments into your particular environmental > requirements. > > When I was in the strip detector business, the preamps were mounted > at the detector, and then there were massive bundles of differentially > driven twisted pairs in ribbon cables ("Twist-N-Flat") running > hundreds of feet to the big electronics. This was pretty "hot stuff" > and in fact the trigger and A/D converters were massive racks cooled > by chilled water. (Now, I also know chilled water is also something > common to plasma experiment cooling!) > > But that was being done with essentially late 70's technology - > electronics had evolved rapidly over the 80's and far more integrated > solutions were coming available. By the early 90's, designs had > realized that all that cabling wasn't optimal - instead integrated > solutions with preamp, trigger, A/D all mounted within inches of the > detector were being done. Again, google "silicon strip detector" to > see the compromises and solutions. > Although, back in the 70's I remember jumping up and down when I discovered the uA733. Tons of bandwidth, modest consumption. I used to do all this stuff with Harris HA2540 and similar chips but they got hot and were very expensive. However, later the ceramic DIP version and the LCC disappeared from the marketplace :-( -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. | |||||||||||||
>
> I'm a research scientists with the Johns Hopkins University, and I'm
> working on a set of designs for an X-ray detector, and trying to spec
> out various methods for obtaining the data we need. One of the designs
> is a system based on diode arrays + amplifiers + ADC system. I've
> already got a good handle on the detector end, and the data
> acquisition system, but I'm stuck on the amplifier system.
>
> We've used commercial amplifiers in the past, but they would likely be
> overkill for our situation, and end up quite pricey on a cost/channel
> basis. Given our specifications, I'm wondering if the optimal solution
> would be to pay for a consultant to develop and test a design
> specifically for our application, and then take that design and punch
> out the number of boards that we would need.
>
> Our generic needs seem to be fairly modest, 100-250kHz bandwidth with
> a gain of 10^7, but as always the devil is in the details. Naturally,
> we want the lowest noise possible so that we can measure signals at
> the nA or sub-nA level.
>
> So, here's the question. Are the specifications and schematic sketch
> shown here:
>
> http://picasaweb.google.com/ktritz/PhotodiodeAmplifierDesign/photo#52...
>
> adequate for a professional to provide a consultation estimate? Would
> the amplifiers be simple enough that a 2nd year EE student could
> manage the design, or are we talking about skirting the bleeding edge?
>
> I'm never contracted a consultant before, so should I expect a
> consulting price tag of $1000? $10000? I'm working with a budget
> that's higher than a hobbyist, but not quite corporation level.
>
> I would also be happy to discuss specific amplifier design ideas.
> Given the capacitance of the detectors in question, I would imagine
> that a very low voltage noise opamp is the way to go, or perhaps a
> JFET front end. The BF862 looks pretty good, and it's relatively high
> capacitance wouldn't matter much compared to the diode.