On Tue, 8 Sep 2020 14:31:19 +0000 (UTC), antispam@math.uni.wroc.pl wrote:>jlarkin@highlandsniptechnology.com wrote: >> >> Even a 10M input, $20 DVM is a decent picoammeter. >> > >Works nice with old meters. But digitally calibrated "10M" DVM >may have 11M input resistance, for such DVM to get any accuracy >one would have to calibrate it and multiply result by correcton >factor, not so nice. Also, significant part of "10M" may be >input leakage.That's not a giant burden, to get a cheap picoammeter. My handheld Flukes are really 10M. It's not hard to check.> >I have nice cheap Chinse meter, lowest range is 10mV with >four digit resolution. Using it I can measure voltage of >a termocouple and see difference when termocouple is on table >and when it is on floor level. One gets funny results >measuring voltage on well discharged polyester capacitor. >There is substantial drift, indicating that most of >input "resistance" is in fact leakage. So, while quite >sensitive this DVM needs external resistor to measure >low currents.I did a little experiment last week: charged a film cap to 5 volts and connected it to my Fluke 8845, on its 10-volt HI-Z range. The DVM slowly charged the cap, at about 15 pA. You can get cheap fA-bias current opamps and make your own very sensitive current meter easily. https://www.dropbox.com/sh/5b2fs47b1qukefv/AAAQgOWmjbeYYsxglN23Py2ya?dl=0 I think there are even better opamps around now. -- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
typically stupid ED article
Started by ●September 1, 2020
Reply by ●September 8, 20202020-09-08
Reply by ●September 8, 20202020-09-08
On Tuesday, September 8, 2020 at 7:59:34 AM UTC-7, John Larkin wrote:> You can get cheap fA-bias current opamps and make your own very > sensitive current meter easily.yeah, but... lots of current meter applications have HV sources, and require protection on the inputs. There's also the little problem of PC board leakage (some teflon standoffs and discrete FETs are the old solutions for this). The real problems with build-your-own are more packaging than semiconductor performance.
Reply by ●September 9, 20202020-09-09
On 2020-09-08 15:38, whit3rd wrote:> On Tuesday, September 8, 2020 at 7:59:34 AM UTC-7, John Larkin wrote: > >> You can get cheap fA-bias current opamps and make your own very >> sensitive current meter easily. > > yeah, but... lots of current meter applications have HV sources, and > require protection on the inputs. There's also the little problem of PC > board leakage (some teflon standoffs and discrete FETs are the old > solutions for this). > > The real problems with build-your-own are more packaging than > semiconductor performance. >For a one-off, just using something like an LMC660CN (quad, 14-pin DIP) mounted dead bug will make a pretty decent femtoammeter. You get 14 low-leakage standoffs for free, and you can use the other sections to bootstrap the input protection circuitry. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●September 9, 20202020-09-09
On Wed, 9 Sep 2020 12:24:50 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2020-09-08 15:38, whit3rd wrote: >> On Tuesday, September 8, 2020 at 7:59:34 AM UTC-7, John Larkin wrote: >> >>> You can get cheap fA-bias current opamps and make your own very >>> sensitive current meter easily. >> >> yeah, but... lots of current meter applications have HV sources, and >> require protection on the inputs. There's also the little problem of PC >> board leakage (some teflon standoffs and discrete FETs are the old >> solutions for this). >> >> The real problems with build-your-own are more packaging than >> semiconductor performance. >> > >For a one-off, just using something like an LMC660CN (quad, 14-pin DIP) >mounted dead bug will make a pretty decent femtoammeter. You get 14 >low-leakage standoffs for free, and you can use the other sections to >bootstrap the input protection circuitry. > >Cheers > >Phil HobbsInsect abuse. I solder a few pins to the copperclad, or use bypass caps as standoffs, and bend the signal pins out. https://www.dropbox.com/s/oegve42oi34kt4e/Live_Bug.jpg?raw=1 (RCA gate. That pic must be pretty old.) I can still see the part number and count in the usual direction. Agree that air is the best insulator, and there's nothing wrong with mid-air junctions. Plastic DIP packages seem to have fA surface leakage. -- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply by ●September 9, 20202020-09-09
On 2020-09-09 13:23, John Larkin wrote:> On Wed, 9 Sep 2020 12:24:50 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 2020-09-08 15:38, whit3rd wrote: >>> On Tuesday, September 8, 2020 at 7:59:34 AM UTC-7, John Larkin wrote: >>> >>>> You can get cheap fA-bias current opamps and make your own very >>>> sensitive current meter easily. >>> >>> yeah, but... lots of current meter applications have HV sources, and >>> require protection on the inputs. There's also the little problem of PC >>> board leakage (some teflon standoffs and discrete FETs are the old >>> solutions for this). >>> >>> The real problems with build-your-own are more packaging than >>> semiconductor performance. >>> >> >> For a one-off, just using something like an LMC660CN (quad, 14-pin DIP) >> mounted dead bug will make a pretty decent femtoammeter. You get 14 >> low-leakage standoffs for free, and you can use the other sections to >> bootstrap the input protection circuitry.> > Insect abuse.At least I put them out of their misery, unlike _some_ people. ;)> I solder a few pins to the copperclad, or use bypass > caps as standoffs, and bend the signal pins out.The pins get weakened a lot when you do that, though. In their natural state they can handle a lot of torque from bending resistor leads and stuff.> https://www.dropbox.com/s/oegve42oi34kt4e/Live_Bug.jpg?raw=1 > > (RCA gate. That pic must be pretty old.) > > I can still see the part number and count in the usual direction.You probably open boiled eggs from the small end, too. That would figure. I just put a gouge in the pin 1 end of the package using dikes, and sometimes scribble the P/N on the copper with a fine-point Sharpie.> > Agree that air is the best insulator, and there's nothing wrong with > mid-air junctions. Plastic DIP packages seem to have fA surface > leakage.Yeah, they're surprisingly good. Of course you can't make a fA op amp with a leaky package. Cheers Phil "the only good bug is a dead bug" Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●September 9, 20202020-09-09
On Wed, 9 Sep 2020 15:29:56 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2020-09-09 13:23, John Larkin wrote: >> On Wed, 9 Sep 2020 12:24:50 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 2020-09-08 15:38, whit3rd wrote: >>>> On Tuesday, September 8, 2020 at 7:59:34 AM UTC-7, John Larkin wrote: >>>> >>>>> You can get cheap fA-bias current opamps and make your own very >>>>> sensitive current meter easily. >>>> >>>> yeah, but... lots of current meter applications have HV sources, and >>>> require protection on the inputs. There's also the little problem of PC >>>> board leakage (some teflon standoffs and discrete FETs are the old >>>> solutions for this). >>>> >>>> The real problems with build-your-own are more packaging than >>>> semiconductor performance. >>>> >>> >>> For a one-off, just using something like an LMC660CN (quad, 14-pin DIP) >>> mounted dead bug will make a pretty decent femtoammeter. You get 14 >>> low-leakage standoffs for free, and you can use the other sections to >>> bootstrap the input protection circuitry. > >> >> Insect abuse. > >At least I put them out of their misery, unlike _some_ people. ;) > >> I solder a few pins to the copperclad, or use bypass >> caps as standoffs, and bend the signal pins out. > >The pins get weakened a lot when you do that, though. In their natural >state they can handle a lot of torque from bending resistor leads and stuff._some_people just get everything right first time.> >> https://www.dropbox.com/s/oegve42oi34kt4e/Live_Bug.jpg?raw=1 >> >> (RCA gate. That pic must be pretty old.) >> >> I can still see the part number and count in the usual direction. > >You probably open boiled eggs from the small end, too. That would figure.Boiling eggs is too much trouble, and I get burned handling them. I have a new egg cooking technique that I will reveal if enough people beg. I was shocked when I tested that ACT04. I was used to CMOS being slow, and its edges were as fast as 10K ECL. And a lot bigger.> >I just put a gouge in the pin 1 end of the package using dikes, and >sometimes scribble the P/N on the copper with a fine-point Sharpie.Call the SPCI. -- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply by ●September 9, 20202020-09-09
On 2020-09-09 18:08, John Larkin wrote:> On Wed, 9 Sep 2020 15:29:56 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 2020-09-09 13:23, John Larkin wrote: >>> On Wed, 9 Sep 2020 12:24:50 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 2020-09-08 15:38, whit3rd wrote: >>>>> On Tuesday, September 8, 2020 at 7:59:34 AM UTC-7, John Larkin wrote: >>>>> >>>>>> You can get cheap fA-bias current opamps and make your own very >>>>>> sensitive current meter easily. >>>>> >>>>> yeah, but... lots of current meter applications have HV sources, and >>>>> require protection on the inputs. There's also the little problem of PC >>>>> board leakage (some teflon standoffs and discrete FETs are the old >>>>> solutions for this). >>>>> >>>>> The real problems with build-your-own are more packaging than >>>>> semiconductor performance. >>>>> >>>> >>>> For a one-off, just using something like an LMC660CN (quad, 14-pin DIP) >>>> mounted dead bug will make a pretty decent femtoammeter. You get 14 >>>> low-leakage standoffs for free, and you can use the other sections to >>>> bootstrap the input protection circuitry. >> >>> >>> Insect abuse. >> >> At least I put them out of their misery, unlike _some_ people. ;) >> >>> I solder a few pins to the copperclad, or use bypass >>> caps as standoffs, and bend the signal pins out. >> >> The pins get weakened a lot when you do that, though. In their natural >> state they can handle a lot of torque from bending resistor leads and stuff. > > _some_people just get everything right first time. > > >> >>> https://www.dropbox.com/s/oegve42oi34kt4e/Live_Bug.jpg?raw=1 >>> >>> (RCA gate. That pic must be pretty old.) >>> >>> I can still see the part number and count in the usual direction. >> >> You probably open boiled eggs from the small end, too. That would figure. > > Boiling eggs is too much trouble, and I get burned handling them. I > have a new egg cooking technique that I will reveal if enough people > beg. > > I was shocked when I tested that ACT04. I was used to CMOS being slow, > and its edges were as fast as 10K ECL. And a lot bigger.Plus the shoot-through and asymmetry teaches you a lot about bypassing.> > >> >> I just put a gouge in the pin 1 end of the package using dikes, and >> sometimes scribble the P/N on the copper with a fine-point Sharpie. > > Call the SPCI.Society for the Promotion of Cool Inventions? Bring 'em on. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●September 10, 20202020-09-10
On Thursday, September 10, 2020 at 8:08:30 AM UTC+10, John Larkin wrote:> On Wed, 9 Sep 2020 15:29:56 -0400, Phil Hobbs > <pcdhSpamM...@electrooptical.net> wrote: > > >On 2020-09-09 13:23, John Larkin wrote: > >> On Wed, 9 Sep 2020 12:24:50 -0400, Phil Hobbs > >> <pcdhSpamM...@electrooptical.net> wrote: > >> > >>> On 2020-09-08 15:38, whit3rd wrote: > >>>> On Tuesday, September 8, 2020 at 7:59:34 AM UTC-7, John Larkin wrote:> I was shocked when I tested that ACT04. I was used to CMOS being slow, > and its edges were as fast as 10K ECL. And a lot bigger.ECL was always designed to drive 50R transmission lines. A 1.2V swing into 50R is 24mA, and that's enough to get the driver warm. National Semiconductors LVDS uses the same voltage swing for the same reason. Most of us have known about this for some forty years now, but John gets shocked when he runs into it. <snip> -- Bill Sloman, Sydney
Reply by ●September 10, 20202020-09-10
torsdag den 10. september 2020 kl. 09.35.07 UTC+2 skrev Bill Sloman:> On Thursday, September 10, 2020 at 8:08:30 AM UTC+10, John Larkin wrote: > > On Wed, 9 Sep 2020 15:29:56 -0400, Phil Hobbs > > <pcdhSpamM...@electrooptical.net> wrote: > > > > >On 2020-09-09 13:23, John Larkin wrote: > > >> On Wed, 9 Sep 2020 12:24:50 -0400, Phil Hobbs > > >> <pcdhSpamM...@electrooptical.net> wrote: > > >> > > >>> On 2020-09-08 15:38, whit3rd wrote: > > >>>> On Tuesday, September 8, 2020 at 7:59:34 AM UTC-7, John Larkin wrote: > > > I was shocked when I tested that ACT04. I was used to CMOS being slow, > > and its edges were as fast as 10K ECL. And a lot bigger. > > ECL was always designed to drive 50R transmission lines. > > A 1.2V swing into 50R is 24mA, and that's enough to get the driver warm. > > National Semiconductors LVDS uses the same voltage swing for the same reason. Most of us have known about this for some forty years now, but John gets shocked when he runs into it. >what are you on about? John saw that an ATC04 was just as fast with a bigger swing and LVDS isn't some National Semiconductors special it is a standard and the swing is only 450mV or 4.5mA
Reply by ●September 10, 20202020-09-10
On Thu, 10 Sep 2020 08:50:35 -0700 (PDT), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>torsdag den 10. september 2020 kl. 09.35.07 UTC+2 skrev Bill Sloman: >> On Thursday, September 10, 2020 at 8:08:30 AM UTC+10, John Larkin wrote: >> > On Wed, 9 Sep 2020 15:29:56 -0400, Phil Hobbs >> > <pcdhSpamM...@electrooptical.net> wrote: >> > >> > >On 2020-09-09 13:23, John Larkin wrote: >> > >> On Wed, 9 Sep 2020 12:24:50 -0400, Phil Hobbs >> > >> <pcdhSpamM...@electrooptical.net> wrote: >> > >> >> > >>> On 2020-09-08 15:38, whit3rd wrote: >> > >>>> On Tuesday, September 8, 2020 at 7:59:34 AM UTC-7, John Larkin wrote: >> >> > I was shocked when I tested that ACT04. I was used to CMOS being slow, >> > and its edges were as fast as 10K ECL. And a lot bigger. >> >> ECL was always designed to drive 50R transmission lines. >> >> A 1.2V swing into 50R is 24mA, and that's enough to get the driver warm. >> >> National Semiconductors LVDS uses the same voltage swing for the same reason. Most of us have known about this for some forty years now, but John gets shocked when he runs into it. >> > >what are you on about? John saw that an ATC04 was just as fast with a bigger swing > >and LVDS isn't some National Semiconductors special it is a standard and the swing is only 450mV or 4.5mAAnd standard ECL swings about 0.8, not 1.2. The voltage across a pulldown resistor could be anything. A few ECL parts, like EL89, swing close to 2 volts. That can be handy. CML usually swings about 0.4 at the termination. I haven't tried them unterminated; I should. We're playing with the idea building a distributed amplifier with discrete fets; I have an EE prof doing the math. The arbitrary goal is to make 50 volt pulses with 50 ps edges. If the output stage works, the next problem will be to come up with a fast gate-line driver with sufficient swing. The problem keeps moving left. The Tek 545 used a distributed amp made from tubes. We should be able to do that with fets. -- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
