Forums

Nanoamp calibrator again

Started by Phil Hobbs May 31, 2012
So, I had a chance to get back to that calibration gizmo for my biochip
front end amplifier (1 nA at the shot noise limit in a 100-MHz BW).

It turns out that it's possible to do a very nice job, assuming that the
integration cap (C1 in the schematic) has zero inductance, but as much
as 0.05 nH blows it out of the water.  (Should have thought of that, of
course, but oh well.)

Try running the sim at
http://electrooptical.net/www/sed/sed.html#Calibrator and see.  

With zero inductance in series with the cap, it switches in well under 1
ns.  (The pHEMT diff pair switches in ~100 ps, and faster if I use more
source current.)  There's a certain amount of cruft in this schematic,
e.g. I probably wouldn't bother with a current source to drive the
sources of the pHEMTs, but you know how these things accumulate as you
go along.

Any bright ideas?

Thanks

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
On Thu, 31 May 2012 15:07:58 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>So, I had a chance to get back to that calibration gizmo for my biochip >front end amplifier (1 nA at the shot noise limit in a 100-MHz BW). > >It turns out that it's possible to do a very nice job, assuming that the >integration cap (C1 in the schematic) has zero inductance, but as much >as 0.05 nH blows it out of the water. (Should have thought of that, of >course, but oh well.) > >Try running the sim at >http://electrooptical.net/www/sed/sed.html#Calibrator and see. > >With zero inductance in series with the cap, it switches in well under 1 >ns. (The pHEMT diff pair switches in ~100 ps, and faster if I use more >source current.) There's a certain amount of cruft in this schematic, >e.g. I probably wouldn't bother with a current source to drive the >sources of the pHEMTs, but you know how these things accumulate as you >go along. > >Any bright ideas? > >Thanks > >Phil Hobbs
"Couldn't find symbol npnsub" -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
John Larkin wrote:
> > On Thu, 31 May 2012 15:07:58 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >So, I had a chance to get back to that calibration gizmo for my biochip > >front end amplifier (1 nA at the shot noise limit in a 100-MHz BW). > > > >It turns out that it's possible to do a very nice job, assuming that the > >integration cap (C1 in the schematic) has zero inductance, but as much > >as 0.05 nH blows it out of the water. (Should have thought of that, of > >course, but oh well.) > > > >Try running the sim at > >http://electrooptical.net/www/sed/sed.html#Calibrator and see. > > > >With zero inductance in series with the cap, it switches in well under 1 > >ns. (The pHEMT diff pair switches in ~100 ps, and faster if I use more > >source current.) There's a certain amount of cruft in this schematic, > >e.g. I probably wouldn't bother with a current source to drive the > >sources of the pHEMTs, but you know how these things accumulate as you > >go along. > > > >Any bright ideas? > > > >Thanks > > > >Phil Hobbs > > "Couldn't find symbol npnsub" >
Fixed--see the web page again. Thanks Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Phil Hobbs a &#2013265929;crit :
> So, I had a chance to get back to that calibration gizmo for my biochip > front end amplifier (1 nA at the shot noise limit in a 100-MHz BW). > > It turns out that it's possible to do a very nice job, assuming that the > integration cap (C1 in the schematic) has zero inductance, but as much > as 0.05 nH blows it out of the water. (Should have thought of that, of > course, but oh well.) > > Try running the sim at > http://electrooptical.net/www/sed/sed.html#Calibrator and see. > > With zero inductance in series with the cap, it switches in well under 1 > ns. (The pHEMT diff pair switches in ~100 ps, and faster if I use more > source current.) There's a certain amount of cruft in this schematic, > e.g. I probably wouldn't bother with a current source to drive the > sources of the pHEMTs, but you know how these things accumulate as you > go along. > > Any bright ideas? > > Thanks > > Phil Hobbs >
I did thought of that then, but for some reason the post didn't get through. Didn't find obvious solutions. Anyway some 'random' thoughts: - lower the cap as much as possible to get a better L/C ratio - use several smaller Cs in // - lowering the cap means you need lower non linear parasitics. One way is to use a resistor as a current source and a low frequency parallel path to linearize the exponential ramp. - esl is a pb so 'eliminate' it, that is induce a compensating emf (have 2 surrounding caps the integrating one, so that it couples a 'counter emf' GND ---||---sig2 sig ---||---GND GND ---||---sig2 With the right caps ratio there might be a solution : ---+------+------+ | | | [R1] [R2] [R1] | | | sig2+ | + sig2 | | | | | | 0.05p | sig+--------------||--> | | | C1 | |C2 |C1 --- M --- M --- --- --- --- | | | | | | GND GND GND M is the mutual between the C1s and C2 Another try might be to precompensate for the L-C high frequency response. Tried it: not so easy :-( Also, for the resistor current source, the parasitic cap might as well be a problem... Finally, maybe you can have 2 coupling pads, one with fast, low amplitude pulse (OK saw tooth) and one with a slower, higher amplitude one for different frequency band of interest. This might ease the L pb somewhat. -- Thanks, Fred.
Phil Hobbs wrote:
> John Larkin wrote: >> On Thu, 31 May 2012 15:07:58 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> So, I had a chance to get back to that calibration gizmo for my biochip >>> front end amplifier (1 nA at the shot noise limit in a 100-MHz BW). >>> >>> It turns out that it's possible to do a very nice job, assuming that the >>> integration cap (C1 in the schematic) has zero inductance, but as much >>> as 0.05 nH blows it out of the water. (Should have thought of that, of >>> course, but oh well.) >>> >>> Try running the sim at >>> http://electrooptical.net/www/sed/sed.html#Calibrator and see. >>> >>> With zero inductance in series with the cap, it switches in well under 1 >>> ns. (The pHEMT diff pair switches in ~100 ps, and faster if I use more >>> source current.) There's a certain amount of cruft in this schematic, >>> e.g. I probably wouldn't bother with a current source to drive the >>> sources of the pHEMTs, but you know how these things accumulate as you >>> go along. >>> >>> Any bright ideas? >>> >>> Thanks >>> >>> Phil Hobbs >> "Couldn't find symbol npnsub" >> > > Fixed--see the web page again. >
I just did but the sym is still missing. Have you built it and tried meandering back and other tricks to neutralize some of the inductance? Can't do that on the simulator though, at least not on LTSpice. -- Regards, Joerg http://www.analogconsultants.com/
On May 31, 3:07=A0pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:
> So, I had a chance to get back to that calibration gizmo for my biochip > front end amplifier (1 nA at the shot noise limit in a 100-MHz BW). > > It turns out that it's possible to do a very nice job, assuming that the > integration cap (C1 in the schematic) has zero inductance, but as much > as 0.05 nH blows it out of the water. =A0(Should have thought of that, of > course, but oh well.) > > Try running the sim athttp://electrooptical.net/www/sed/sed.html#Calibrat=
orand see.
> > With zero inductance in series with the cap, it switches in well under 1 > ns. =A0(The pHEMT diff pair switches in ~100 ps, and faster if I use more > source current.) =A0There's a certain amount of cruft in this schematic, > e.g. I probably wouldn't bother with a current source to drive the > sources of the pHEMTs, but you know how these things accumulate as you > go along. > > Any bright ideas?
Only the brute force approach. (Is L4 the 'offending' inductance and C10 the gimmick?) Less C, more R and more V. Could you make the C a transmission line type thing? George H.
> > Thanks > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC > Optics, Electro-optics, Photonics, Analog Electronics > > 160 North State Road #203 > Briarcliff Manor NY 10510 > 845-480-2058 > > hobbs at electrooptical dot nethttp://electrooptical.net
Phil Hobbs wrote:
> So, I had a chance to get back to that calibration gizmo for my biochip > front end amplifier (1 nA at the shot noise limit in a 100-MHz BW). > > It turns out that it's possible to do a very nice job, assuming that the > integration cap (C1 in the schematic) has zero inductance, but as much > as 0.05 nH blows it out of the water. (Should have thought of that, of > course, but oh well.) > > Try running the sim at > http://electrooptical.net/www/sed/sed.html#Calibrator and see. > > With zero inductance in series with the cap, it switches in well under 1 > ns. (The pHEMT diff pair switches in ~100 ps, and faster if I use more > source current.) There's a certain amount of cruft in this schematic, > e.g. I probably wouldn't bother with a current source to drive the > sources of the pHEMTs, but you know how these things accumulate as you > go along. > > Any bright ideas? > > Thanks > > Phil Hobbs >
OOPS! tried the LTC program and got the following errors: Questionable use of curly braces in "symattr spiceline rser=0.005 lser={lcap}" Error: undefined symbol in: "[lcap]" Questionable use of curly braces in "symattr value {lbead}" Error: undefined symbol in: "[lbead]" Questionable use of curly braces in "symattr spiceline rpar={rpbead}" Error: undefined symbol in: "[rpbead]" Questionable use of curly braces in "symattr value {rbi}" Error: undefined symbol in: "[rbi]" Questionable use of curly braces in "symattr value {lbead}" Error: undefined symbol in: "[lbead]" Questionable use of curly braces in "symattr spiceline rpar={rpbead}" Error: undefined symbol in: "[rpbead]" Questionable use of curly braces in "symattr value {lbead}" Error: undefined symbol in: "[lbead]" Questionable use of curly braces in "symattr spiceline rpar={rpbead}" Error: undefined symbol in: "[rpbead]" Questionable use of curly braces in "symattr value {lbead}" Error: undefined symbol in: "[lbead]" Questionable use of curly braces in "symattr spiceline rpar={rpbead}" Error: undefined symbol in: "[rpbead]" Questionable use of curly braces in "symattr value {lbead}" Error: undefined symbol in: "[lbead]" Questionable use of curly braces in "symattr spiceline rpar={rpbead}" Error: undefined symbol in: "[rpbead]" Circuit: Version 4 Fatal Error: Multiple instances of "Flag" Maybe one of the problems was that all of the files were in a folder on another drive.
John Larkin wrote:
> On Thu, 31 May 2012 15:07:58 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> So, I had a chance to get back to that calibration gizmo for my biochip >> front end amplifier (1 nA at the shot noise limit in a 100-MHz BW). >> >> It turns out that it's possible to do a very nice job, assuming that the >> integration cap (C1 in the schematic) has zero inductance, but as much >> as 0.05 nH blows it out of the water. (Should have thought of that, of >> course, but oh well.) >> >> Try running the sim at >> http://electrooptical.net/www/sed/sed.html#Calibrator and see. >> >> With zero inductance in series with the cap, it switches in well under 1 >> ns. (The pHEMT diff pair switches in ~100 ps, and faster if I use more >> source current.) There's a certain amount of cruft in this schematic, >> e.g. I probably wouldn't bother with a current source to drive the >> sources of the pHEMTs, but you know how these things accumulate as you >> go along. >> >> Any bright ideas? >> >> Thanks >> >> Phil Hobbs > > "Couldn't find symbol npnsub" > >
Look harder..
Fred Bartoli wrote:
> Phil Hobbs a &#2013265929;crit : >> So, I had a chance to get back to that calibration gizmo for my biochip >> front end amplifier (1 nA at the shot noise limit in a 100-MHz BW). >> >> It turns out that it's possible to do a very nice job, assuming that the >> integration cap (C1 in the schematic) has zero inductance, but as much >> as 0.05 nH blows it out of the water. (Should have thought of that, of >> course, but oh well.) >> >> Try running the sim at >> http://electrooptical.net/www/sed/sed.html#Calibrator and see. >> With zero inductance in series with the cap, it switches in well under 1 >> ns. (The pHEMT diff pair switches in ~100 ps, and faster if I use more >> source current.) There's a certain amount of cruft in this schematic, >> e.g. I probably wouldn't bother with a current source to drive the >> sources of the pHEMTs, but you know how these things accumulate as you >> go along. >> >> Any bright ideas? >> >> Thanks >> >> Phil Hobbs >> > > I did thought of that then, but for some reason the post didn't get > through. > > Didn't find obvious solutions. Anyway some 'random' thoughts: > > - lower the cap as much as possible to get a better L/C ratio > - use several smaller Cs in // > - lowering the cap means you need lower non linear parasitics. One way > is to use a resistor as a current source and a low frequency parallel > path to linearize the exponential ramp. > - esl is a pb so 'eliminate' it, that is induce a compensating emf (have > 2 surrounding caps the integrating one, so that it couples a 'counter emf' > > GND ---||---sig2 > sig ---||---GND > GND ---||---sig2 > > With the right caps ratio there might be a solution : > > ---+------+------+ > | | | > [R1] [R2] [R1] > | | | > sig2+ | + sig2 > | | | > | | | 0.05p > | sig+--------------||--> > | | | > C1 | |C2 |C1 > --- M --- M --- > --- --- --- > | | | > | | | > GND GND GND > > M is the mutual between the C1s and C2
* Cute!
> > Another try might be to precompensate for the L-C high frequency > response. Tried it: not so easy :-(
* Or maybe some feed forward or some positive feedback?
> > Also, for the resistor current source, the parasitic cap might as well > be a problem... > > Finally, maybe you can have 2 coupling pads, one with fast, low > amplitude pulse (OK saw tooth) and one with a slower, higher amplitude > one for different frequency band of interest. This might ease the L pb > somewhat. >
Joerg wrote:
> Phil Hobbs wrote: >> John Larkin wrote: >>> On Thu, 31 May 2012 15:07:58 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> So, I had a chance to get back to that calibration gizmo for my biochip >>>> front end amplifier (1 nA at the shot noise limit in a 100-MHz BW). >>>> >>>> It turns out that it's possible to do a very nice job, assuming that the >>>> integration cap (C1 in the schematic) has zero inductance, but as much >>>> as 0.05 nH blows it out of the water. (Should have thought of that, of >>>> course, but oh well.) >>>> >>>> Try running the sim at >>>> http://electrooptical.net/www/sed/sed.html#Calibrator and see. >>>> >>>> With zero inductance in series with the cap, it switches in well under 1 >>>> ns. (The pHEMT diff pair switches in ~100 ps, and faster if I use more >>>> source current.) There's a certain amount of cruft in this schematic, >>>> e.g. I probably wouldn't bother with a current source to drive the >>>> sources of the pHEMTs, but you know how these things accumulate as you >>>> go along. >>>> >>>> Any bright ideas? >>>> >>>> Thanks >>>> >>>> Phil Hobbs >>> "Couldn't find symbol npnsub" >>> >> >> Fixed--see the web page again. >> > > I just did but the sym is still missing. Have you built it and tried > meandering back and other tricks to neutralize some of the inductance? > Can't do that on the simulator though, at least not on LTSpice. >
Check; it disliked the ASC - a fair bunch of errors.