Robert Baer wrote:> > 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.Weird. All of those are defined right there in the .asc, which runs fine here. I took some suggestions and added a few more tweaks, including a critically damped RLC filter at the output, and it looks okay now with 1 nH in series with each of 10 parallelled 39 pF capacitors. The transient gate current of pHEMTs can be pretty significant when you're only running them at 70 uA I_D. Also the beta linearity and Early voltage of PNP RF transistors is really, really horrible. With reasonably realistic strays put in, it looks like the transients are all over in a nanosecond, and they're not a lot larger than the DC, so it should reproduce the 3.5 ns rise time of the preamp pretty well. Cheers 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
Nanoamp calibrator again
Started by ●May 31, 2012
Reply by ●June 1, 20122012-06-01
Reply by ●June 1, 20122012-06-01
On Jun 1, 5:31=A0pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> Robert Baer wrote: > > > Phil Hobbs wrote: > > > So, I had a chance to get back to that calibration gizmo for my bioch=ip> > > 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 muc=h> > > 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 at > > >http://electrooptical.net/www/sed/sed.html#Calibratorand see. > > > > With zero inductance in series with the cap, it switches in well unde=r 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 schemat=ic,> > > 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 yo=u> > > go along. > > > > Any bright ideas? > > > > Thanks > > > > Phil Hobbs > > > =A0 =A0OOPS! tried the LTC program and got the following errors: > > Questionable use of curly braces in "symattr spiceline rser=3D0.005 > > lser=3D{lcap}" > > =A0 =A0 =A0Error: undefined symbol in: "[lcap]" > > Questionable use of curly braces in "symattr value {lbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[lbead]" > > Questionable use of curly braces in "symattr spiceline rpar=3D{rpbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[rpbead]" > > Questionable use of curly braces in "symattr value {rbi}" > > =A0 =A0 =A0Error: undefined symbol in: "[rbi]" > > Questionable use of curly braces in "symattr value {lbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[lbead]" > > Questionable use of curly braces in "symattr spiceline rpar=3D{rpbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[rpbead]" > > Questionable use of curly braces in "symattr value {lbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[lbead]" > > Questionable use of curly braces in "symattr spiceline rpar=3D{rpbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[rpbead]" > > Questionable use of curly braces in "symattr value {lbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[lbead]" > > Questionable use of curly braces in "symattr spiceline rpar=3D{rpbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[rpbead]" > > Questionable use of curly braces in "symattr value {lbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[lbead]" > > Questionable use of curly braces in "symattr spiceline rpar=3D{rpbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[rpbead]" > > Circuit: Version 4 > > > Fatal Error: Multiple instances of "Flag" > > =A0 =A0Maybe one of the problems was that all of the files were in a fo=lder> > on another drive. > > Weird. =A0All of those are defined right there in the .asc, which runs > fine here. > > I took some suggestions and added a few more tweaks, including a > critically damped RLC filter at the output, and it looks okay now with 1 > nH in series with each of 10 parallelled 39 pF capacitors.Excellent! (that's semi-brute force) George H.> > The transient gate current of pHEMTs can be pretty significant when > you're only running them at 70 uA I_D. =A0Also the beta linearity and > Early voltage of PNP RF transistors is really, really horrible. > > With reasonably realistic strays put in, it looks like the transients > are all over in a nanosecond, and they're not a lot larger than the DC, > so it should reproduce the 3.5 ns rise time of the preamp pretty well. > > Cheers > > 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- Hide quoted tex=t -> > - Show quoted text -
Reply by ●June 2, 20122012-06-02
On Fri, 01 Jun 2012 13:49:45 -0800, Robert Baer wrote:> 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.Ran first time for me. -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
Reply by ●June 2, 20122012-06-02
On Jun 2, 6:16=A0pm, Fred Abse <excretatau...@invalid.invalid> wrote:> On Fri, 01 Jun 2012 13:49:45 -0800, Robert Baer wrote: > > =A0 =A0OOPS! tried the LTC program and got the following errors: > > Questionable use of curly braces in "symattr spiceline rser=3D0.005 > > lser=3D{lcap}" > > =A0 =A0 =A0Error: undefined symbol in: "[lcap]" > > Questionable use of curly braces in "symattr value {lbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[lbead]" > > Questionable use of curly braces in "symattr spiceline rpar=3D{rpbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[rpbead]" > > Questionable use of curly braces in "symattr value {rbi}" > > =A0 =A0 =A0Error: undefined symbol in: "[rbi]" > > Questionable use of curly braces in "symattr value {lbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[lbead]" > > Questionable use of curly braces in "symattr spiceline rpar=3D{rpbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[rpbead]" > > Questionable use of curly braces in "symattr value {lbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[lbead]" > > Questionable use of curly braces in "symattr spiceline rpar=3D{rpbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[rpbead]" > > Questionable use of curly braces in "symattr value {lbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[lbead]" > > Questionable use of curly braces in "symattr spiceline rpar=3D{rpbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[rpbead]" > > Questionable use of curly braces in "symattr value {lbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[lbead]" > > Questionable use of curly braces in "symattr spiceline rpar=3D{rpbead}" > > =A0 =A0 =A0Error: undefined symbol in: "[rpbead]" > > Circuit: Version 4 > > > Fatal Error: Multiple instances of "Flag" > > =A0 =A0Maybe one of the problems was that all of the files were in a fo=lder> > on another drive. > > Ran first time for me.Lucky you. I just got a long string of error messages, suggesting that whatever end-of-line symbol Phil uses in his longer Spice command strings isn't recognised as such by my version of LTSpice. -- Bill Sloman, Nijmegen
Reply by ●June 2, 20122012-06-02
Fred Abse wrote:> > On Fri, 01 Jun 2012 13:49:45 -0800, Robert Baer wrote: > > > 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. > > Ran first time for me.I posted a rebiased version that runs off +5V and gets the edge artifacts down to something reasonable. It uses single-ended drive for the pHEMT differential pair Z2/Z3, in order to prevent capacitive gate current in Z3 from corrupting the output. Using ten 39 pF caps in parallel reduces the equivalent series inductance, and adding an RLC filter to the output makes the transition a lot cleaner. The output as before is I(C5). The simulation shows all sorts of ripples at up to 12 GHz elsewhere in the circuit, which I really don't think are real. (The pHEMTs are that fast at 20 mA of drain current, but surely not at 70 uA.) Anyway, I think this can be made to work, assuming that the layout person knows something about RF. Cheers 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
Reply by ●June 2, 20122012-06-02
Bill Sloman wrote:> > On Jun 2, 6:16 pm, Fred Abse <excretatau...@invalid.invalid> wrote: > > On Fri, 01 Jun 2012 13:49:45 -0800, Robert Baer wrote: > > > 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. > > > > Ran first time for me. > > Lucky you. I just got a long string of error messages, suggesting that > whatever end-of-line symbol Phil uses in his longer Spice command > strings isn't recognised as such by my version of LTSpice. > > -- > Bill Sloman, NijmegenI took the .asc file and copied it directly to the web host using sftp. I suspect that your client mungs the line endings somehow. Cheers 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
Reply by ●June 2, 20122012-06-02
Phil Hobbs wrote:> Fred Abse wrote: >> On Fri, 01 Jun 2012 13:49:45 -0800, Robert Baer wrote: >> >>> 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. >> Ran first time for me. > > > I posted a rebiased version that runs off +5V and gets the edge > artifacts down to something reasonable.I still get "Couldn't find symbol npnsub". It uses single-ended drive for> the pHEMT differential pair Z2/Z3, in order to prevent capacitive gate > current in Z3 from corrupting the output. Using ten 39 pF caps in > parallel reduces the equivalent series inductance, and adding an RLC > filter to the output makes the transition a lot cleaner. > > The output as before is I(C5). The simulation shows all sorts of > ripples at up to 12 GHz elsewhere in the circuit, which I really don't > think are real. (The pHEMTs are that fast at 20 mA of drain current, > but surely not at 70 uA.) > > Anyway, I think this can be made to work, assuming that the layout > person knows something about RF. >And think about tricks like meander-back to reduce inductance. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●June 2, 20122012-06-02
Joerg wrote:> > Phil Hobbs wrote: > > Fred Abse wrote: > >> On Fri, 01 Jun 2012 13:49:45 -0800, Robert Baer wrote: > >> > >>> 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. > >> Ran first time for me. > > > > > > I posted a rebiased version that runs off +5V and gets the edge > > artifacts down to something reasonable. > > I still get "Couldn't find symbol npnsub".The .asy file is there on the webpage--the LTspice NPN symbol doesn't work with a subcircuit, so I had to make another one.> > It uses single-ended drive for > > the pHEMT differential pair Z2/Z3, in order to prevent capacitive gate > > current in Z3 from corrupting the output. Using ten 39 pF caps in > > parallel reduces the equivalent series inductance, and adding an RLC > > filter to the output makes the transition a lot cleaner. > > > > The output as before is I(C5). The simulation shows all sorts of > > ripples at up to 12 GHz elsewhere in the circuit, which I really don't > > think are real. (The pHEMTs are that fast at 20 mA of drain current, > > but surely not at 70 uA.) > > > > Anyway, I think this can be made to work, assuming that the layout > > person knows something about RF. > > > > And think about tricks like meander-back to reduce inductance.Care to expound? Cheers 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
Reply by ●June 2, 20122012-06-02
Robert Baer 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" >> >> > Look harder..It's usually best to include all non-standard models right inside the SPICE file and then declare a regular parts a subcircuit. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●June 2, 20122012-06-02
Joerg wrote:> > Robert Baer 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" > >> > >> > > Look harder.. > > It's usually best to include all non-standard models right inside the > SPICE file and then declare a regular parts a subcircuit.The BFP640FESD model is sort of large and complicated, and I don't think you can put a symbol in a .asc file--can you? Cheers 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
