On Thu, 12 May 2022 10:43:14 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Arie de Muijnck wrote: >> On 2022-05-12 00:30, John Larkin wrote: >> >>> 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. >> >> AFAIK, it's not the base current but base voltage that controls the >> collector current. The base current is just an unfortunate side effect. >> The relation between them happens to be rather constant, hence the idea >> that hfe is the main factor. Ideally, the base 'leakage' could be so low >> that base current electrons can be counted. In that case, would the much >> higher collector current come in packets? >> >> Arie > >Yup, a BJT is a transconductance device with a loss mechanism >(recombination in the base region) that produces leakage current. IIRC >Mikko Kiviranta or somebody said that the beta of a BFP650 goes up to >above 10000 at low temperature. > >Cheers > >Phil HobbsA transistor has c-b leakage, Is of the c-b diode, so turns itself on with the base open. Spice at least suggests that any amount of added base current increases collector current. That said, I don't understand this: Version 4 SHEET 1 880 680 WIRE 288 80 272 80 WIRE 304 80 288 80 WIRE 416 80 384 80 WIRE 272 128 272 80 WIRE 416 144 416 80 WIRE 176 176 144 176 WIRE 208 176 176 176 WIRE 144 208 144 176 WIRE 272 288 272 224 WIRE 416 288 416 224 WIRE 144 320 144 288 FLAG 272 288 0 FLAG 416 288 0 FLAG 144 320 0 FLAG 176 176 B FLAG 288 80 C SYMBOL npn 208 128 R0 WINDOW 0 83 28 Left 2 WINDOW 3 56 54 Left 2 SYMATTR InstName Q1 SYMATTR Value 2N5550 SYMBOL voltage 416 128 R0 WINDOW 0 49 37 Left 2 WINDOW 3 54 64 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL current 144 288 R180 WINDOW 0 54 35 Left 2 WINDOW 3 24 0 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName I1 SYMATTR Value SINE(0 100f 1) SYMBOL res 400 64 R90 WINDOW 0 -8 51 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 1 TEXT 56 144 Left 2 !.tran 2 TEXT 528 184 Left 2 !.op abstol 1e-18 TEXT 528 216 Left 2 !.op gmin 1e-18 TEXT 0 56 Left 2 ;Low current NPN test TEXT 32 88 Left 2 ;JL May 12 2022 -- 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
BJT behaviour at ridiculously low current levels
Started by ●May 11, 2022
Reply by ●May 12, 20222022-05-12
Reply by ●May 12, 20222022-05-12
Phil Hobbs wrote:> Don wrote: >> Arie de Muijnck wrote: >>> John Larkin wrote: >>> >>>> 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. >>> >>> AFAIK, it's not the base current but base voltage that controls the >>> collector current. The base current is just an unfortunate side effect. >>> The relation between them happens to be rather constant, hence the idea >>> that hfe is the main factor. Ideally, the base 'leakage' could be so low >>> that base current electrons can be counted. In that case, would the much >>> higher collector current come in packets? >> >> Good point. You must be within the active region to use the hybrid model >> to ignore transconductance. > > Don't ever ignore transconductance."Hybrid" (as used by me above) is arguably ambiguous. "Hybrid equivalent" puts a finer point on it. And it indeed ignores transconductance: https://upload.wikimedia.org/wikipedia/commons/9/9f/BJT_h-parameters_(generalised).svg Danke, -- Don, KB7RPU, https://www.qsl.net/kb7rpu There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night.
Reply by ●May 12, 20222022-05-12
Don wrote:> Phil Hobbs wrote: >> Don wrote: >>> Arie de Muijnck wrote: >>>> John Larkin wrote: >>>> >>>>> 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. >>>> >>>> AFAIK, it's not the base current but base voltage that controls the >>>> collector current. The base current is just an unfortunate side effect. >>>> The relation between them happens to be rather constant, hence the idea >>>> that hfe is the main factor. Ideally, the base 'leakage' could be so low >>>> that base current electrons can be counted. In that case, would the much >>>> higher collector current come in packets? >>> >>> Good point. You must be within the active region to use the hybrid model >>> to ignore transconductance. >> >> Don't ever ignore transconductance. > > "Hybrid" (as used by me above) is arguably ambiguous. "Hybrid > equivalent" puts a finer point on it. And it indeed ignores > transconductance: > > https://upload.wikimedia.org/wikipedia/commons/9/9f/BJT_h-parameters_(generalised).svg > > Danke, >Of course it does. That's why nobody ever uses it for anything real AFAICT. The only reference I ever make to the h model is the current gain, because it's easy to keep the distinction between small-signal (h_FE) and large-signal (H_FE) straight. One could use upper- and lowercase beta, but uppercase beta is indistinguishable from B. You can turn LEDs on and off ignoring g_M, or make a rule-of-thumb single-ended CE amplifier with emitter degeneration. For anything differential, you use g_M for the design and beta for the sanity check. Beta is a useful number, mostly because it warns you about things you can't do, but even in beta-graded parts it varies by a factor of 2, whereas the transconductance of any two BJTs at the same collector current and same temperature, of whatever size, of whatever make, matches to a tiny fraction of 1%, at least at collector currents where beta is vaguely reasonable. 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 12, 20222022-05-12
John Larkin wrote:> On Thu, 12 May 2022 10:43:14 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> Arie de Muijnck wrote: >>> On 2022-05-12 00:30, John Larkin wrote: >>> >>>> 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. >>> >>> AFAIK, it's not the base current but base voltage that controls the >>> collector current. The base current is just an unfortunate side effect. >>> The relation between them happens to be rather constant, hence the idea >>> that hfe is the main factor. Ideally, the base 'leakage' could be so low >>> that base current electrons can be counted. In that case, would the much >>> higher collector current come in packets? >>> >>> Arie >> >> Yup, a BJT is a transconductance device with a loss mechanism >> (recombination in the base region) that produces leakage current. IIRC >> Mikko Kiviranta or somebody said that the beta of a BFP650 goes up to >> above 10000 at low temperature. >> >> Cheers >> >> Phil Hobbs > > A transistor has c-b leakage, Is of the c-b diode, so turns itself on > with the base open. Spice at least suggests that any amount of added > base current increases collector current. > > That said, I don't understand this:<snip> I went into the control panel and set chgtol and absolute current tolerance to 1E-18, and it works fine. Hopefully JT is smiling indulgently somewhere. ;) 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 12, 20222022-05-12
On Wednesday, May 11, 2022 at 3:30:14 PM UTC-7, John Larkin wrote:> 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.The other numbers are important. A single-electron level is noise (recombination noise) in a semiconductor of any useful size. Transistor base and emitter contacts for most packages are dozens of microns, so discrete transistor volumes are on the order of 5E-5 cubic centimeters. At 1.4 x 10E10 charge carriers per cc, for silicon, there's mobile electrons and holes by the thousands in a transistor-size piece of nonconducting (undoped) silicon. A doped transistor has... more. It takes sizeable base charge to get above the noise.
Reply by ●May 12, 20222022-05-12
On Thu, 12 May 2022 15:01:06 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>John Larkin wrote: >> On Thu, 12 May 2022 10:43:14 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> Arie de Muijnck wrote: >>>> On 2022-05-12 00:30, John Larkin wrote: >>>> >>>>> 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. >>>> >>>> AFAIK, it's not the base current but base voltage that controls the >>>> collector current. The base current is just an unfortunate side effect. >>>> The relation between them happens to be rather constant, hence the idea >>>> that hfe is the main factor. Ideally, the base 'leakage' could be so low >>>> that base current electrons can be counted. In that case, would the much >>>> higher collector current come in packets? >>>> >>>> Arie >>> >>> Yup, a BJT is a transconductance device with a loss mechanism >>> (recombination in the base region) that produces leakage current. IIRC >>> Mikko Kiviranta or somebody said that the beta of a BFP650 goes up to >>> above 10000 at low temperature. >>> >>> Cheers >>> >>> Phil Hobbs >> >> A transistor has c-b leakage, Is of the c-b diode, so turns itself on >> with the base open. Spice at least suggests that any amount of added >> base current increases collector current. >> >> That said, I don't understand this: ><snip> > >I went into the control panel and set chgtol and absolute current >tolerance to 1E-18, and it works fine. > >Hopefully JT is smiling indulgently somewhere. ;) > >Cheers > >Phil HobbsWhat I don't understand is why the sine wave current source doesn't make a sine wave of current. -- 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 12, 20222022-05-12
On Thursday, May 12, 2022 at 1:20:11 PM UTC-7, John Larkin wrote:> >John Larkin wrote:> >> A transistor has c-b leakage, Is of the c-b diode, so turns itself on > >> with the base open. Spice at least suggests that any amount of added > >> base current increases collector current.> What I don't understand is why the sine wave current source doesn't > make a sine wave of current.The base sees leakage plus a sinewave. How could that sum be proportional to a sinewave, when your applied signal is a sine, but leakage is a non-negligible constant?
Reply by ●May 12, 20222022-05-12
John Larkin wrote:> On Thu, 12 May 2022 15:01:06 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> John Larkin wrote: >>> On Thu, 12 May 2022 10:43:14 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> Arie de Muijnck wrote: >>>>> On 2022-05-12 00:30, John Larkin wrote: >>>>> >>>>>> 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. >>>>> >>>>> AFAIK, it's not the base current but base voltage that controls the >>>>> collector current. The base current is just an unfortunate side effect. >>>>> The relation between them happens to be rather constant, hence the idea >>>>> that hfe is the main factor. Ideally, the base 'leakage' could be so low >>>>> that base current electrons can be counted. In that case, would the much >>>>> higher collector current come in packets? >>>>> >>>>> Arie >>>> >>>> Yup, a BJT is a transconductance device with a loss mechanism >>>> (recombination in the base region) that produces leakage current. IIRC >>>> Mikko Kiviranta or somebody said that the beta of a BFP650 goes up to >>>> above 10000 at low temperature. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> A transistor has c-b leakage, Is of the c-b diode, so turns itself on >>> with the base open. Spice at least suggests that any amount of added >>> base current increases collector current. >>> >>> That said, I don't understand this: >> <snip> >> >> I went into the control panel and set chgtol and absolute current >> tolerance to 1E-18, and it works fine. >> >> Hopefully JT is smiling indulgently somewhere. ;) >> >> Cheers >> >> Phil Hobbs > > What I don't understand is why the sine wave current source doesn't > make a sine wave of current. >Right, but if you hack at the control panel as above, it does. See <https://electrooptical.net/www/sed/JLpuzzle.png>. 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 12, 20222022-05-12
On Thu, 12 May 2022 13:34:27 -0700 (PDT), whit3rd <whit3rd@gmail.com> wrote:>On Thursday, May 12, 2022 at 1:20:11 PM UTC-7, John Larkin wrote: > >> >John Larkin wrote: > >> >> A transistor has c-b leakage, Is of the c-b diode, so turns itself on >> >> with the base open. Spice at least suggests that any amount of added >> >> base current increases collector current. > >> What I don't understand is why the sine wave current source doesn't >> make a sine wave of current. > >The base sees leakage plus a sinewave. How could that sum be >proportional to a sinewave, when your applied signal is a sine, >but leakage is a non-negligible constant?A current source shouldn't care about its load. It should make its programmed current. -- Anybody can count to one. - Robert Widlar
Reply by ●May 13, 20222022-05-13
On Thu, 12 May 2022 16:41:47 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>John Larkin wrote: >> On Thu, 12 May 2022 15:01:06 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> John Larkin wrote: >>>> On Thu, 12 May 2022 10:43:14 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> Arie de Muijnck wrote: >>>>>> On 2022-05-12 00:30, John Larkin wrote: >>>>>> >>>>>>> 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. >>>>>> >>>>>> AFAIK, it's not the base current but base voltage that controls the >>>>>> collector current. The base current is just an unfortunate side effect. >>>>>> The relation between them happens to be rather constant, hence the idea >>>>>> that hfe is the main factor. Ideally, the base 'leakage' could be so low >>>>>> that base current electrons can be counted. In that case, would the much >>>>>> higher collector current come in packets? >>>>>> >>>>>> Arie >>>>> >>>>> Yup, a BJT is a transconductance device with a loss mechanism >>>>> (recombination in the base region) that produces leakage current. IIRC >>>>> Mikko Kiviranta or somebody said that the beta of a BFP650 goes up to >>>>> above 10000 at low temperature. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> A transistor has c-b leakage, Is of the c-b diode, so turns itself on >>>> with the base open. Spice at least suggests that any amount of added >>>> base current increases collector current. >>>> >>>> That said, I don't understand this: >>> <snip> >>> >>> I went into the control panel and set chgtol and absolute current >>> tolerance to 1E-18, and it works fine. >>> >>> Hopefully JT is smiling indulgently somewhere. ;) >>> >>> Cheers >>> >>> Phil Hobbs >> >> What I don't understand is why the sine wave current source doesn't >> make a sine wave of current. >> > >Right, but if you hack at the control panel as above, it does. > >See <https://electrooptical.net/www/sed/JLpuzzle.png>. > >Cheers > >Phil HobbsI can get the current source to make a sine wave if I skip the initial operating point solution, uic, with your spice settings, but the collector current is goofy, a 250 Hz triangle. One issue is maybe the roughly negative 1 gigavolt swing on the base. -- Anybody can count to one. - Robert Widlar
