On Tue, 12 Feb 2013 11:59:36 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 02/11/2013 05:29 PM, mike wrote: >> On 2/11/2013 10:42 AM, Phil Hobbs wrote: >>> Hi, all--I'm looking for a curve tracer. Ideally it would be >>> USB-powered, and come with software that would make plots and =generate>>> data files. Nothing too fancy, just I_C and I_B vs V_CE and V_BE, and >>> the equivalent for FETs. A plus would be automatic computation of =beta,>>> V_GSth, Early voltage, and even some of the DC SPICE parameters like >>> emitter and base resistance. >>> >>> It would be especially nice if it could measure gate current with a >>> resolution of a picoamp or less. >>> >>> Any suggestions? >>> >>> Cheers >>> >>> Phil Hobbs >>> >> You're asking a LOT. >> >> A curve tracer is a qualitative measurement device. >> I use a TEK 7CT1N for simple stuff and only drag out the 576 >> when I gotta have it. I use it more for blowing shorts >> out of NiCd's than for testing transistors. > >It's only qualitative because it only has a CRT readout. A curve tracer==20>is a sort of stripped-down version of a semiconductor parameter analyzer==20>such as an HP4145B, which is very quantitative indeed. (I wouldn't mind==20>one of those--I used to have one at my PPOE, but it takes a lot of rack=20 >space.) >> >> If you try to make one using a series of fixed measurements >> and graphing them, you get mixed results. I tried that back in the =day.>> The device thermal time constants significantly affect the measurement >> details. > >Yup. You have to be quick about it if you're dissipating any=20 >significant power. Of course with a MCU and DACs, you can do the=20 >measurements out of order to keep the average dissipation constant. > >> >> And the parasitics of the test fixture swamp device parasitics, unless=you>> use network analyzer fixturing. > >Not necessarily. My Boonton 72BD easily measures a few femtofarads.=20 >You just null it out before attaching the hot lead to the device. > >> >> Picoamps to amps is a wide dynamic range and will require some serious >> attention to range switching. >> >> Not saying it can't be done, just that it's not nearly as simple as it >> sounds. > >I don't need amps--I'd be quite happy with a 50-100 mA top end. Most of==20>what I need a curve tracer for is measuring weird RF devices with lousy=20 >datasheets. > >Cheers > >Phil HobbsOh foo, the fixturing for RF devices can get really weird and expensive. Those will be on you if we get together and create a USB curve tracer. ?-)
Curve tracers
Started by ●February 11, 2013
Reply by ●February 13, 20132013-02-13
Reply by ●February 13, 20132013-02-13
josephkk wrote:> > On Mon, 11 Feb 2013 21:21:55 -0500, "Michael A. Terrell" > <mike.terrell@earthlink.net> wrote: > > > > >tm wrote: > >> > >> This might be worth $24 to explore. Needs +/- 15 volts and a XY scope. > > > > > > $2 less in kit form. I have 25 new Integrated power designs > >SRW-65-4006 switching power supplies with +/= 15V outputs. > > > > > >http://034262c.netsolhost.com/wp-content/uploads/2011/06/SRW-65%20Specs.pdf > > That is a nice old time experimenters supply. Are they available?I'll have to find the box, but I have 25 NOS out in the shop. I'll let you know when i find them.
Reply by ●February 13, 20132013-02-13
On Tue, 12 Feb 2013 21:57:13 -0800, josephkk <joseph_barrett@sbcglobal.net> wrote:>On Tue, 12 Feb 2013 11:59:36 -0500, Phil Hobbs ><pcdhSpamMeSenseless@electrooptical.net> wrote: > >>On 02/11/2013 05:29 PM, mike wrote: >>> On 2/11/2013 10:42 AM, Phil Hobbs wrote: >>>> Hi, all--I'm looking for a curve tracer. Ideally it would be >>>> USB-powered, and come with software that would make plots and generate >>>> data files. Nothing too fancy, just I_C and I_B vs V_CE and V_BE, and >>>> the equivalent for FETs. A plus would be automatic computation of beta, >>>> V_GSth, Early voltage, and even some of the DC SPICE parameters like >>>> emitter and base resistance. >>>> >>>> It would be especially nice if it could measure gate current with a >>>> resolution of a picoamp or less. >>>> >>>> Any suggestions? >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>>> >>> You're asking a LOT. >>> >>> A curve tracer is a qualitative measurement device. >>> I use a TEK 7CT1N for simple stuff and only drag out the 576 >>> when I gotta have it. I use it more for blowing shorts >>> out of NiCd's than for testing transistors. >> >>It's only qualitative because it only has a CRT readout. A curve tracer >>is a sort of stripped-down version of a semiconductor parameter analyzer >>such as an HP4145B, which is very quantitative indeed. (I wouldn't mind >>one of those--I used to have one at my PPOE, but it takes a lot of rack >>space.) >>> >>> If you try to make one using a series of fixed measurements >>> and graphing them, you get mixed results. I tried that back in the day. >>> The device thermal time constants significantly affect the measurement >>> details. >> >>Yup. You have to be quick about it if you're dissipating any >>significant power. Of course with a MCU and DACs, you can do the >>measurements out of order to keep the average dissipation constant. >> >>> >>> And the parasitics of the test fixture swamp device parasitics, unless you >>> use network analyzer fixturing. >> >>Not necessarily. My Boonton 72BD easily measures a few femtofarads. >>You just null it out before attaching the hot lead to the device. >> >>> >>> Picoamps to amps is a wide dynamic range and will require some serious >>> attention to range switching. >>> >>> Not saying it can't be done, just that it's not nearly as simple as it >>> sounds. >> >>I don't need amps--I'd be quite happy with a 50-100 mA top end. Most of >>what I need a curve tracer for is measuring weird RF devices with lousy >>datasheets. >> >>Cheers >> >>Phil Hobbs > >Oh foo, the fixturing for RF devices can get really weird and expensive. >Those will be on you if we get together and create a USB curve tracer. > >?-)The problem with a lot of (most) RF devices is their terrible DC characterization. Like, no DC curves at all. The s-params give you a rough idea of the high-speed behavior. RF data sheets often say to just adjust the bias until it works. The specified breakdown voltage specs are not useful, because sometimes they assume, without saying so, that the drain voltage can swing to multiples of the supply voltage, and factor that in. Parts spec'd at 6 volts can cheerfully avalanche at 25. A detector diode might be spec'd a 2 volts reverse, woth no curves at all, because they figure that's all a detector user needs to know. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●February 13, 20132013-02-13
On 2/13/2013 12:35 AM, josephkk wrote:> On Mon, 11 Feb 2013 17:25:17 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> >>> Hey, doesn't one of your kids want to get his hands dirty with some >>> software work? If you charge the client a lower rate for that work he >>> could still sock away a lot of money towards his first souped-up TransAm >>> with mag wheels and all that :-) >>> >> >> Brr. My son is _not_ "going to drive me to drinkin'" if I can help it, >> but anyway that wouldn't be his style. He's busy writing Arm Cortex M3 >> firmware at the moment, but since he's learning C at the same time, he >> isn't fast at it yet. (He did get a task switcher working, using a >> linked list of tasks handled by the systick interrupt handler.) > > Hey it may be a bit basic, but it works. It is an adequate approach for > very simple rate monotonic schedulers but the linked list time will start > to hurt if things get complicated and crowded schedule wise. He needs to > separate the switcher from the task manager. Then schedule time for the > task manger as a task. >>It isn't really a multitasking OS, just a way of scheduling stuff for future reference, e.g. looking after a delta-sigma ADC that needs a 3-million clock reset interval. For now the list elements consist of a time stamp, a pointer to a flag variable, and the tail pointer. The systick interrupt just looks at the next thing in the list to see if the time stamp matches, and if so, pops the element, sets the flag, and checks the next one in case it has the same time stamp. All the work is done by functions called from the housekeeping loop. None of them takes enough time that it needs to be preempted--it's quick stuff like setting up a DMA to redraw the screen, taking a data point, sending a character to the USB serial port, that sort of stuff. (I've been doing embedded stuff off and on for a dozen or so years, but I'm nobody's idea of an expert at it.) 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 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 13, 20132013-02-13
On 2/13/2013 10:24 AM, John Larkin wrote:> On Tue, 12 Feb 2013 21:57:13 -0800, josephkk <joseph_barrett@sbcglobal.net> > wrote: > >> On Tue, 12 Feb 2013 11:59:36 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 02/11/2013 05:29 PM, mike wrote: >>>> On 2/11/2013 10:42 AM, Phil Hobbs wrote: >>>>> Hi, all--I'm looking for a curve tracer. Ideally it would be >>>>> USB-powered, and come with software that would make plots and generate >>>>> data files. Nothing too fancy, just I_C and I_B vs V_CE and V_BE, and >>>>> the equivalent for FETs. A plus would be automatic computation of beta, >>>>> V_GSth, Early voltage, and even some of the DC SPICE parameters like >>>>> emitter and base resistance. >>>>> >>>>> It would be especially nice if it could measure gate current with a >>>>> resolution of a picoamp or less. >>>>> >>>>> Any suggestions? >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>>> >>>> You're asking a LOT. >>>> >>>> A curve tracer is a qualitative measurement device. >>>> I use a TEK 7CT1N for simple stuff and only drag out the 576 >>>> when I gotta have it. I use it more for blowing shorts >>>> out of NiCd's than for testing transistors. >>> >>> It's only qualitative because it only has a CRT readout. A curve tracer >>> is a sort of stripped-down version of a semiconductor parameter analyzer >>> such as an HP4145B, which is very quantitative indeed. (I wouldn't mind >>> one of those--I used to have one at my PPOE, but it takes a lot of rack >>> space.) >>>> >>>> If you try to make one using a series of fixed measurements >>>> and graphing them, you get mixed results. I tried that back in the day. >>>> The device thermal time constants significantly affect the measurement >>>> details. >>> >>> Yup. You have to be quick about it if you're dissipating any >>> significant power. Of course with a MCU and DACs, you can do the >>> measurements out of order to keep the average dissipation constant. >>> >>>> >>>> And the parasitics of the test fixture swamp device parasitics, unless you >>>> use network analyzer fixturing. >>> >>> Not necessarily. My Boonton 72BD easily measures a few femtofarads. >>> You just null it out before attaching the hot lead to the device. >>> >>>> >>>> Picoamps to amps is a wide dynamic range and will require some serious >>>> attention to range switching. >>>> >>>> Not saying it can't be done, just that it's not nearly as simple as it >>>> sounds. >>> >>> I don't need amps--I'd be quite happy with a 50-100 mA top end. Most of >>> what I need a curve tracer for is measuring weird RF devices with lousy >>> datasheets. >>> >>> Cheers >>> >>> Phil Hobbs >> >> Oh foo, the fixturing for RF devices can get really weird and expensive. >> Those will be on you if we get together and create a USB curve tracer. >> >> ?-) > > The problem with a lot of (most) RF devices is their terrible DC > characterization. Like, no DC curves at all. The s-params give you a rough idea > of the high-speed behavior. > > RF data sheets often say to just adjust the bias until it works. The specified > breakdown voltage specs are not useful, because sometimes they assume, without > saying so, that the drain voltage can swing to multiples of the supply voltage, > and factor that in. Parts spec'd at 6 volts can cheerfully avalanche at 25. A > detector diode might be spec'd a 2 volts reverse, woth no curves at all, because > they figure that's all a detector user needs to know.I'm normally working down on the low frequency end anyway, e.g. a 100 MHz biochip front end using 14-GHz pHEMTs and 40-GHz bipolars, so simple concepts like C_JC and R_BB' still work OK. Boontons rule! 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 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 13, 20132013-02-13
On 2/11/2013 8:06 PM, Dimitrij Klingbeil wrote:> "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message > news:362dnefOFo3kpoTMnZ2dnUVZ_oCdnZ2d@supernews.com... >> Hi, all--I'm looking for a curve tracer. Ideally it would be USB-powered, >> and come with software that would make plots and generate data files. >> Nothing too fancy, just I_C and I_B vs V_CE and V_BE, and the equivalent >> for FETs. A plus would be automatic computation of beta, V_GSth, Early >> voltage, and even some of the DC SPICE parameters like emitter and base >> resistance. >> >> It would be especially nice if it could measure gate current with a >> resolution of a picoamp or less. >> >> Any suggestions? >> >> Cheers >> >> Phil Hobbs > > Hello > > It looks like simple but working curve tracers are going unobtainium these > days. It's either modular high-end systems for IC Fabs with the prices > skyrocketing up the ISS or the homegrown fleabay stuff designed by people > with no grasp of anything beyound current shunt resistors. > > There's a lot of hobby project schematics published in a hidden corners of > the web that very nearly miss ending up on http://www.thedailywtf.com but > only because the daily WTF does not know they exist (and does not care much > about test equipment either). Also there are some boat anchors in unknown > condition for sale, sometimes way overpriced because audiophools use the > higher-voltage models in order to match tubes (whoever sells the QT2, > listen, there's a new market for you). > > It looks like there's just no supply of affordable and usable curve tracers > in the western corners of the world. There's a lot of Chinese curve tracers > available, mostly analog ones, but the Chinese see no market for them in the > west and don't even bother offering export versions with English user > manuals or sometimes even front panel texts. Even worse, English-speaking > search engines have difficulties finding anything, so most types are only > findable with the proper "native" search terms. > > The "classic" instruments are really heavy (look up "QT2" for example, that > thing is still produced) and haven't heared about a digital interface (or > about the last 4 decades for that matter). > > There are newer versions like http://bayimg.com/KAjeIAAei (XJ4836). It's > mains powered, but it at least has an USB interface. It's a rather sensitive > small-signal tracer (by local standards), collector current down to > 100nA/div, but no way for it to measure picoamps. Somewhat pricey too, given > its specs, but at least it is standalone, PC-less and it is supposed to > store settings and plots somewhere nonvolatile. > > If you search further, you may find the WQ4828 to WQ4830 type curve tracers > too ( http://www.hzwqdz.com/ ), but they only go down to 200nA/div and their > user interface will be a completely non-intuitive guesswork to anyone who > does not have some Chinese friends to help translate it. They seem to be > able to calculate more parameters however. > >Thanks. I agree, it seems like a vast wasteland. 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 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 13, 20132013-02-13
On Wed, 13 Feb 2013 11:01:28 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2/13/2013 10:24 AM, John Larkin wrote: >> On Tue, 12 Feb 2013 21:57:13 -0800, josephkk <joseph_barrett@sbcglobal.net> >> wrote: >> >>> On Tue, 12 Feb 2013 11:59:36 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 02/11/2013 05:29 PM, mike wrote: >>>>> On 2/11/2013 10:42 AM, Phil Hobbs wrote: >>>>>> Hi, all--I'm looking for a curve tracer. Ideally it would be >>>>>> USB-powered, and come with software that would make plots and generate >>>>>> data files. Nothing too fancy, just I_C and I_B vs V_CE and V_BE, and >>>>>> the equivalent for FETs. A plus would be automatic computation of beta, >>>>>> V_GSth, Early voltage, and even some of the DC SPICE parameters like >>>>>> emitter and base resistance. >>>>>> >>>>>> It would be especially nice if it could measure gate current with a >>>>>> resolution of a picoamp or less. >>>>>> >>>>>> Any suggestions? >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>>> >>>>> You're asking a LOT. >>>>> >>>>> A curve tracer is a qualitative measurement device. >>>>> I use a TEK 7CT1N for simple stuff and only drag out the 576 >>>>> when I gotta have it. I use it more for blowing shorts >>>>> out of NiCd's than for testing transistors. >>>> >>>> It's only qualitative because it only has a CRT readout. A curve tracer >>>> is a sort of stripped-down version of a semiconductor parameter analyzer >>>> such as an HP4145B, which is very quantitative indeed. (I wouldn't mind >>>> one of those--I used to have one at my PPOE, but it takes a lot of rack >>>> space.) >>>>> >>>>> If you try to make one using a series of fixed measurements >>>>> and graphing them, you get mixed results. I tried that back in the day. >>>>> The device thermal time constants significantly affect the measurement >>>>> details. >>>> >>>> Yup. You have to be quick about it if you're dissipating any >>>> significant power. Of course with a MCU and DACs, you can do the >>>> measurements out of order to keep the average dissipation constant. >>>> >>>>> >>>>> And the parasitics of the test fixture swamp device parasitics, unless you >>>>> use network analyzer fixturing. >>>> >>>> Not necessarily. My Boonton 72BD easily measures a few femtofarads. >>>> You just null it out before attaching the hot lead to the device. >>>> >>>>> >>>>> Picoamps to amps is a wide dynamic range and will require some serious >>>>> attention to range switching. >>>>> >>>>> Not saying it can't be done, just that it's not nearly as simple as it >>>>> sounds. >>>> >>>> I don't need amps--I'd be quite happy with a 50-100 mA top end. Most of >>>> what I need a curve tracer for is measuring weird RF devices with lousy >>>> datasheets. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> Oh foo, the fixturing for RF devices can get really weird and expensive. >>> Those will be on you if we get together and create a USB curve tracer. >>> >>> ?-) >> >> The problem with a lot of (most) RF devices is their terrible DC >> characterization. Like, no DC curves at all. The s-params give you a rough idea >> of the high-speed behavior. >> >> RF data sheets often say to just adjust the bias until it works. The specified >> breakdown voltage specs are not useful, because sometimes they assume, without >> saying so, that the drain voltage can swing to multiples of the supply voltage, >> and factor that in. Parts spec'd at 6 volts can cheerfully avalanche at 25. A >> detector diode might be spec'd a 2 volts reverse, woth no curves at all, because >> they figure that's all a detector user needs to know. > >I'm normally working down on the low frequency end anyway, e.g. a 100 >MHz biochip front end using 14-GHz pHEMTs and 40-GHz bipolars, so simple >concepts like C_JC and R_BB' still work OK. Boontons rule!Right. You have to make your own curves, like C-vs-V. That's why a USB curve tracer should measure capacitances, too. Heck, somebody here with a curve tracer and a Booonton could set up a garage operation to characterize parts for a fee. Modelithics does that for big bucks. -- 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
Reply by ●February 13, 20132013-02-13
On 2/13/2013 11:30 AM, John Larkin wrote:> On Wed, 13 Feb 2013 11:01:28 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 2/13/2013 10:24 AM, John Larkin wrote: >>> On Tue, 12 Feb 2013 21:57:13 -0800, josephkk <joseph_barrett@sbcglobal.net> >>> wrote: >>> >>>> On Tue, 12 Feb 2013 11:59:36 -0500, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 02/11/2013 05:29 PM, mike wrote: >>>>>> On 2/11/2013 10:42 AM, Phil Hobbs wrote: >>>>>>> Hi, all--I'm looking for a curve tracer. Ideally it would be >>>>>>> USB-powered, and come with software that would make plots and generate >>>>>>> data files. Nothing too fancy, just I_C and I_B vs V_CE and V_BE, and >>>>>>> the equivalent for FETs. A plus would be automatic computation of beta, >>>>>>> V_GSth, Early voltage, and even some of the DC SPICE parameters like >>>>>>> emitter and base resistance. >>>>>>> >>>>>>> It would be especially nice if it could measure gate current with a >>>>>>> resolution of a picoamp or less. >>>>>>> >>>>>>> Any suggestions? >>>>>>> >>>>>>> Cheers >>>>>>> >>>>>>> Phil Hobbs >>>>>>> >>>>>> You're asking a LOT. >>>>>> >>>>>> A curve tracer is a qualitative measurement device. >>>>>> I use a TEK 7CT1N for simple stuff and only drag out the 576 >>>>>> when I gotta have it. I use it more for blowing shorts >>>>>> out of NiCd's than for testing transistors. >>>>> >>>>> It's only qualitative because it only has a CRT readout. A curve tracer >>>>> is a sort of stripped-down version of a semiconductor parameter analyzer >>>>> such as an HP4145B, which is very quantitative indeed. (I wouldn't mind >>>>> one of those--I used to have one at my PPOE, but it takes a lot of rack >>>>> space.) >>>>>> >>>>>> If you try to make one using a series of fixed measurements >>>>>> and graphing them, you get mixed results. I tried that back in the day. >>>>>> The device thermal time constants significantly affect the measurement >>>>>> details. >>>>> >>>>> Yup. You have to be quick about it if you're dissipating any >>>>> significant power. Of course with a MCU and DACs, you can do the >>>>> measurements out of order to keep the average dissipation constant. >>>>> >>>>>> >>>>>> And the parasitics of the test fixture swamp device parasitics, unless you >>>>>> use network analyzer fixturing. >>>>> >>>>> Not necessarily. My Boonton 72BD easily measures a few femtofarads. >>>>> You just null it out before attaching the hot lead to the device. >>>>> >>>>>> >>>>>> Picoamps to amps is a wide dynamic range and will require some serious >>>>>> attention to range switching. >>>>>> >>>>>> Not saying it can't be done, just that it's not nearly as simple as it >>>>>> sounds. >>>>> >>>>> I don't need amps--I'd be quite happy with a 50-100 mA top end. Most of >>>>> what I need a curve tracer for is measuring weird RF devices with lousy >>>>> datasheets. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> Oh foo, the fixturing for RF devices can get really weird and expensive. >>>> Those will be on you if we get together and create a USB curve tracer. >>>> >>>> ?-) >>> >>> The problem with a lot of (most) RF devices is their terrible DC >>> characterization. Like, no DC curves at all. The s-params give you a rough idea >>> of the high-speed behavior. >>> >>> RF data sheets often say to just adjust the bias until it works. The specified >>> breakdown voltage specs are not useful, because sometimes they assume, without >>> saying so, that the drain voltage can swing to multiples of the supply voltage, >>> and factor that in. Parts spec'd at 6 volts can cheerfully avalanche at 25. A >>> detector diode might be spec'd a 2 volts reverse, woth no curves at all, because >>> they figure that's all a detector user needs to know. >> >> I'm normally working down on the low frequency end anyway, e.g. a 100 >> MHz biochip front end using 14-GHz pHEMTs and 40-GHz bipolars, so simple >> concepts like C_JC and R_BB' still work OK. Boontons rule! > > Right. You have to make your own curves, like C-vs-V. That's why a USB > curve tracer should measure capacitances, too. > > Heck, somebody here with a curve tracer and a Booonton could set up a > garage operation to characterize parts for a fee. Modelithics does > that for big bucks. > >Have you measured the leakage of the Boonton's biasing system? Maybe one could just hang a little board on the back of one, and do it that way. 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 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 13, 20132013-02-13
On Wed, 13 Feb 2013 11:34:36 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2/13/2013 11:30 AM, John Larkin wrote: >> On Wed, 13 Feb 2013 11:01:28 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 2/13/2013 10:24 AM, John Larkin wrote: >>>> On Tue, 12 Feb 2013 21:57:13 -0800, josephkk <joseph_barrett@sbcglobal.net> >>>> wrote: >>>> >>>>> On Tue, 12 Feb 2013 11:59:36 -0500, Phil Hobbs >>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> >>>>>> On 02/11/2013 05:29 PM, mike wrote: >>>>>>> On 2/11/2013 10:42 AM, Phil Hobbs wrote: >>>>>>>> Hi, all--I'm looking for a curve tracer. Ideally it would be >>>>>>>> USB-powered, and come with software that would make plots and generate >>>>>>>> data files. Nothing too fancy, just I_C and I_B vs V_CE and V_BE, and >>>>>>>> the equivalent for FETs. A plus would be automatic computation of beta, >>>>>>>> V_GSth, Early voltage, and even some of the DC SPICE parameters like >>>>>>>> emitter and base resistance. >>>>>>>> >>>>>>>> It would be especially nice if it could measure gate current with a >>>>>>>> resolution of a picoamp or less. >>>>>>>> >>>>>>>> Any suggestions? >>>>>>>> >>>>>>>> Cheers >>>>>>>> >>>>>>>> Phil Hobbs >>>>>>>> >>>>>>> You're asking a LOT. >>>>>>> >>>>>>> A curve tracer is a qualitative measurement device. >>>>>>> I use a TEK 7CT1N for simple stuff and only drag out the 576 >>>>>>> when I gotta have it. I use it more for blowing shorts >>>>>>> out of NiCd's than for testing transistors. >>>>>> >>>>>> It's only qualitative because it only has a CRT readout. A curve tracer >>>>>> is a sort of stripped-down version of a semiconductor parameter analyzer >>>>>> such as an HP4145B, which is very quantitative indeed. (I wouldn't mind >>>>>> one of those--I used to have one at my PPOE, but it takes a lot of rack >>>>>> space.) >>>>>>> >>>>>>> If you try to make one using a series of fixed measurements >>>>>>> and graphing them, you get mixed results. I tried that back in the day. >>>>>>> The device thermal time constants significantly affect the measurement >>>>>>> details. >>>>>> >>>>>> Yup. You have to be quick about it if you're dissipating any >>>>>> significant power. Of course with a MCU and DACs, you can do the >>>>>> measurements out of order to keep the average dissipation constant. >>>>>> >>>>>>> >>>>>>> And the parasitics of the test fixture swamp device parasitics, unless you >>>>>>> use network analyzer fixturing. >>>>>> >>>>>> Not necessarily. My Boonton 72BD easily measures a few femtofarads. >>>>>> You just null it out before attaching the hot lead to the device. >>>>>> >>>>>>> >>>>>>> Picoamps to amps is a wide dynamic range and will require some serious >>>>>>> attention to range switching. >>>>>>> >>>>>>> Not saying it can't be done, just that it's not nearly as simple as it >>>>>>> sounds. >>>>>> >>>>>> I don't need amps--I'd be quite happy with a 50-100 mA top end. Most of >>>>>> what I need a curve tracer for is measuring weird RF devices with lousy >>>>>> datasheets. >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>> >>>>> Oh foo, the fixturing for RF devices can get really weird and expensive. >>>>> Those will be on you if we get together and create a USB curve tracer. >>>>> >>>>> ?-) >>>> >>>> The problem with a lot of (most) RF devices is their terrible DC >>>> characterization. Like, no DC curves at all. The s-params give you a rough idea >>>> of the high-speed behavior. >>>> >>>> RF data sheets often say to just adjust the bias until it works. The specified >>>> breakdown voltage specs are not useful, because sometimes they assume, without >>>> saying so, that the drain voltage can swing to multiples of the supply voltage, >>>> and factor that in. Parts spec'd at 6 volts can cheerfully avalanche at 25. A >>>> detector diode might be spec'd a 2 volts reverse, woth no curves at all, because >>>> they figure that's all a detector user needs to know. >>> >>> I'm normally working down on the low frequency end anyway, e.g. a 100 >>> MHz biochip front end using 14-GHz pHEMTs and 40-GHz bipolars, so simple >>> concepts like C_JC and R_BB' still work OK. Boontons rule! >> >> Right. You have to make your own curves, like C-vs-V. That's why a USB >> curve tracer should measure capacitances, too. >> >> Heck, somebody here with a curve tracer and a Booonton could set up a >> garage operation to characterize parts for a fee. Modelithics does >> that for big bucks. >> >> > >Have you measured the leakage of the Boonton's biasing system? Maybe >one could just hang a little board on the back of one, and do it that way. > >Cheers > >Phil HobbsGood idea. Design the USB curve tracer to run through a Boonton 72 to get the capacitances. The Boonton has an analog output on the back. But it would be more fun to do it ourselves. -- 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
Reply by ●February 13, 20132013-02-13
On Tue, 12 Feb 2013 15:30:25 -0800, mike wrote:> Methinks you're applying apples thinking to oranges. If you take a > measurement at a fixed operating point, whether it be DC or pulsed, your > average junction temperature is likely to be different from what it would > be in an analog curve tracer like the 576. All those measurement points > are not likely to line up on exactly the same line you'd see with an > analog plot. Nothing wrong with that. If you want data at a particular > operating point, that's the way to go. > If you want a curve tracer, like it says in the subject line, you may not > see what you expect.The basic 576 *incorporates* pulsed measurements, as well as swept. 300 microseconds and 80 microseconds. Bottom row of buttons on the right hand side. It does that at a single operating point at a time, if you want a plot, you have to draw it by hand. Methinks you are not that familiar with the 576. I use one or other of the two in my lab on an almost daily basis. The 176 is an addon unit that fits in place of the standard test fixture, that goes to 200 amps. It is pulsed mode only, using delay line charge storage, to avoid enormous, heavy power supplies, unlike the 175, that needed two people or a fork truck to carry it. -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)
