Hi, I am experimenting with ultra-low power ideas and I was able to simulate a 30Hz relaxation oscillator running at 45nA/1V. I am waiting for the delivery of high-value resistors, but the same oscillator with resistors scaled down 10x works on the bench and consumes ~380nA/3V/360Hz which is still pretty awesome. This real device has been made of BSS123/BSS84 operating in the subthreshold realm -- the highest AC p-p voltage I can observe is ~500mV. There is a lot of interesting papers on subthreshold mode, so it is all good. But, out of curiosity, I replaced the FETs with BC847C/BC857C and it appears to work (in LTSpice!) even better, with V_BE sort of 350mV. I admit, no prototype so far. I didn't expect this -- could you please you recommend me some good book/papers on BJTs operated at nA levels? I would like to learn the theory in a proper way, as inferring it from a SPICE behavioural model might not be the best way to go. For example, it looks like the beta is extremely high there, even exponential. Does this BJT mode have a googlable name? Best regards, Piotr
BJT behaviour at ridiculously low current levels
Started by ●May 11, 2022
Reply by ●May 11, 20222022-05-11
On Wednesday, May 11, 2022 at 11:39:29 AM UTC-7, Piotr Wyderski wrote:> Hi, > > I am experimenting with ultra-low power ideas and I was able to simulate > a 30Hz relaxation oscillator running at 45nA/1V....> recommend me some good book/papers on BJTs operated at nA levels? > I would like to learn the theory in a proper way, as inferring it from a > SPICE behavioural model might not be the best way to go. For example, it > looks like the beta is extremely high there, even exponential. Does this > BJT mode have a googlable name?Alas, it's a region that has high dependence on collector leakage currents (and cosmic rays, etc). Some of the space-rated research does get into this, because radiation damage moves the effects into higher-current parts of the characteristic. Beta is 'high' because the collector leakage is adding to the external base wire's contribution. It takes negative base bias to get an 'off' state, through Rbb resistance (base spreading resistance).
Reply by ●May 11, 20222022-05-11
On Wed, 11 May 2022 20:39:08 +0200, Piotr Wyderski <bombald@protonmail.com> wrote:>Hi, > >I am experimenting with ultra-low power ideas and I was able to simulate >a 30Hz relaxation oscillator running at 45nA/1V. I am waiting for the >delivery of high-value resistors, but the same oscillator with resistors >scaled down 10x works on the bench and consumes ~380nA/3V/360Hz which is >still pretty awesome. > >This real device has been made of BSS123/BSS84 operating in the >subthreshold realm -- the highest AC p-p voltage I can observe is >~500mV. There is a lot of interesting papers on subthreshold mode, so it >is all good. > >But, out of curiosity, I replaced the FETs with BC847C/BC857C and it >appears to work (in LTSpice!) even better, with V_BE sort of 350mV. >I admit, no prototype so far. I didn't expect this -- could you please >you recommend me some good book/papers on BJTs operated at nA levels? >I would like to learn the theory in a proper way, as inferring it from a >SPICE behavioural model might not be the best way to go. For example, it >looks like the beta is extremely high there, even exponential. Does this >BJT mode have a googlable name? > > Best regards, Piotr > >There is a niche of building oscillators that run at very low supply voltages, ballpark 10 mV. I think jfets do pretty good. A depletion PHEMT might be good too. -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
Reply by ●May 11, 20222022-05-11
John Larkin wrote:> There is a niche of building oscillators that run at very low supply > voltages, ballpark 10 mV. I think jfets do pretty good.Yes, there are several interesting examples. The lowest voltage I know of is 20mV. But in this off-time research application related to the recent CeraCharge purchase I am trying to minimize current consumption, not voltage. It can stop oscillating at 1.2V, no problem with that. But if the current could be as low as 20nA, that would be something. Best regards, Piotr
Reply by ●May 11, 20222022-05-11
On Wed, 11 May 2022 21:23:17 +0200, Piotr Wyderski <bombald@protonmail.com> wrote:>John Larkin wrote: > >> There is a niche of building oscillators that run at very low supply >> voltages, ballpark 10 mV. I think jfets do pretty good. > >Yes, there are several interesting examples. The lowest voltage I know >of is 20mV. But in this off-time research application related to the >recent CeraCharge purchase I am trying to minimize current consumption, >not voltage. It can stop oscillating at 1.2V, no problem with that. But >if the current could be as low as 20nA, that would be something. > > Best regards, PiotrThe AOE X-chapter book has some data on using BJTs at pA levels. Section 2x.9 2N4401 holds up pretty well at Ic of 100 pA. I'd expect some very small RF transistors to be pretty good. -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
Reply by ●May 11, 20222022-05-11
Piotr Wyderski wrote:> Hi, > > I am experimenting with ultra-low power ideas and I was able to simulate > a 30Hz relaxation oscillator running at 45nA/1V. I am waiting for the > delivery of high-value resistors, but the same oscillator with resistors > scaled down 10x works on the bench and consumes ~380nA/3V/360Hz which is > still pretty awesome. > > This real device has been made of BSS123/BSS84 operating in the > subthreshold realm -- the highest AC p-p voltage I can observe is > ~500mV. There is a lot of interesting papers on subthreshold mode, so it > is all good. > > But, out of curiosity, I replaced the FETs with BC847C/BC857C and it > appears to work (in LTSpice!) even better, with V_BE sort of 350mV. > I admit, no prototype so far. I didn't expect this -- could you please > you recommend me some good book/papers on BJTs operated at nA levels? > I would like to learn the theory in a proper way, as inferring it from a > SPICE behavioural model might not be the best way to go. For example, it > looks like the beta is extremely high there, even exponential. Does this > BJT mode have a googlable name? > > Best regards, PiotrLots of small BJTs work fine in the low nanoamps. I've used BFT25As as transdiodes down to 5 nA or so. They crapped out about 1 nA. The transconductance is a lot better than FETs down there! 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 ●May 11, 20222022-05-11
John Larkin wrote:> On Wed, 11 May 2022 21:23:17 +0200, Piotr Wyderski > <bombald@protonmail.com> wrote: > >> John Larkin wrote: >> >>> There is a niche of building oscillators that run at very low supply >>> voltages, ballpark 10 mV. I think jfets do pretty good. >> >> Yes, there are several interesting examples. The lowest voltage I know >> of is 20mV. But in this off-time research application related to the >> recent CeraCharge purchase I am trying to minimize current consumption, >> not voltage. It can stop oscillating at 1.2V, no problem with that. But >> if the current could be as low as 20nA, that would be something. >> >> Best regards, Piotr > > The AOE X-chapter book has some data on using BJTs at pA levels. > Section 2x.9 > > 2N4401 holds up pretty well at Ic of 100 pA. I'd expect some very > small RF transistors to be pretty good. > > >The f_T goes in the tank--at 1 nA, even a BFT25A is a < 1-MHz transistor. 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 ●May 11, 20222022-05-11
Phil Hobbs wrote:> Lots of small BJTs work fine in the low nanoamps. I've used BFT25As as > transdiodes down to 5 nA or so. They crapped out about 1 nA.This is getting really interesting. I didn't know that BJTs have useful subthreshold region too.> The transconductance is a lot better than FETs down there!Indeed, Spice appears to say the same. I need to build a JFET probe in order not to disturb the single electron microcosmos down there with a dingy default 1Meg probe. And grab some radial resistors in the range of 47Meg+, as I don't fancy the idea of connecting hordes of 4.7Meg ones to get there. Best regards, Piotr
Reply by ●May 11, 20222022-05-11
On Wed, 11 May 2022 17:14:08 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>John Larkin wrote: >> On Wed, 11 May 2022 21:23:17 +0200, Piotr Wyderski >> <bombald@protonmail.com> wrote: >> >>> John Larkin wrote: >>> >>>> There is a niche of building oscillators that run at very low supply >>>> voltages, ballpark 10 mV. I think jfets do pretty good. >>> >>> Yes, there are several interesting examples. The lowest voltage I know >>> of is 20mV. But in this off-time research application related to the >>> recent CeraCharge purchase I am trying to minimize current consumption, >>> not voltage. It can stop oscillating at 1.2V, no problem with that. But >>> if the current could be as low as 20nA, that would be something. >>> >>> Best regards, Piotr >> >> The AOE X-chapter book has some data on using BJTs at pA levels. >> Section 2x.9 >> >> 2N4401 holds up pretty well at Ic of 100 pA. I'd expect some very >> small RF transistors to be pretty good. >> >> >> > >The f_T goes in the tank--at 1 nA, even a BFT25A is a < 1-MHz transistor. > >Cheers > >Phil HobbsWell, 1 pA into 1 pF gets you 1 volt per second. Speed takes power. Big savings on heat sinks! -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
Reply by ●May 11, 20222022-05-11
On Wed, 11 May 2022 23:38:24 +0200, Piotr Wyderski <bombald@protonmail.com> wrote:>Phil Hobbs wrote: > >> Lots of small BJTs work fine in the low nanoamps.� I've used BFT25As as >> transdiodes down to 5 nA or so.� They crapped out about 1 nA. > >This is getting really interesting. I didn't know that BJTs have useful >subthreshold region too.I was theorizing that an LED, at low current, wouldn't have enough voltage across it to make visible photons. A typical green LED runs about 80 mV per decade current. I tried some green LEDs at 1 nA and they made visible light. I conjecture (ie guess) that base current makes collector current down at the single-electron level. 1 pA is just 6 milion electrons per second. -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
