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BJT behaviour at ridiculously low current levels

Started by Piotr Wyderski ●May 11, 2022
Reply by Phil Hobbs ●May 13, 20222022-05-13
jlarkin@highlandsniptechnology.com wrote:

> 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. ;)



>>>
>>> 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>.



> 
> I 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.


Nice and well-behaved for me, just tightening up all the tolerances 
(including some on the compression page of the control panel, which 
isn't shown on the screen shots).

<https://electrooptical.net/www/sed/JLpuzzle2.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 John S ●May 13, 20222022-05-13
On 5/12/2022 3:19 PM, 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.
> 



Works great!

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TEXT 32 88 Left 2 ;JL May 12 2022
Reply by Hul Tytus ●May 14, 20222022-05-14
Piotr  you might look at the hc cmos series. They will operate in
the 1 volt range with the expected lower current. One maker spoke 
of characterizing their devices at one something volts. 
   I experimented with those supply voltages for devices
working in the 100k cps area and all seemed pheasable.

Hul


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
Reply by ●May 14, 20222022-05-14
On Fri, 13 May 2022 21:45:10 -0500, John S <Sophi.2@invalid.org>
wrote:


>On 5/12/2022 3:19 PM, 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.
>> 
>
>
>Works great!


Not really. If yoy disconnect the base, the current source still
swings +- 100 mv. That depends on some Spice settings.




>
>Version 4
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>WIRE 304 80 288 80
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>SYMATTR Value SINE(0 100f 1)
>SYMBOL res -112 112 R0
>SYMATTR InstName R2
>SYMATTR Value 1g
>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



-- 

Anybody can count to one.

- Robert Widlar
Reply by piglet ●May 14, 20222022-05-14
On 14/05/2022 07:04, Hul Tytus wrote:

> Piotr  you might look at the hc cmos series. They will operate in
> the 1 volt range with the expected lower current. One maker spoke
> of characterizing their devices at one something volts.
>     I experimented with those supply voltages for devices
> working in the 100k cps area and all seemed pheasable.
> 
> Hul
> 


Yes, I actually experienced HC cmos retaining stored latch states down 
into tens of millivolts region. However to make any kind of oscillator 
means passing slowly through a linear region and current consumption 
will shoot up. To make an oscillator a discrete design with high value 
series resistors might be better, this draws an average 10nA to make 
narrow pulses every 8-9 secs...

Version 4
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WIRE 32 -640 -208 -640
WIRE 336 -640 32 -640
WIRE 864 -640 336 -640
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SYMATTR Value 10Meg
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WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 10Meg
TEXT -242 360 Left 2 !.tran 100
TEXT 928 336 Left 2 ;EPW SED MAY 2022
TEXT 928 288 Left 2 ;Nano power pulser



piglet
Reply by Hul Tytus ●May 14, 20222022-05-14
Good point for an osicilator. The 10's of millivolts range you mention
is an interesting area.

Hul


piglet <erichpwagner@hotmail.com> wrote:

> On 14/05/2022 07:04, Hul Tytus wrote:
> > Piotr  you might look at the hc cmos series. They will operate in
> > the 1 volt range with the expected lower current. One maker spoke
> > of characterizing their devices at one something volts.
> >     I experimented with those supply voltages for devices
> > working in the 100k cps area and all seemed pheasable.
> > 
> > Hul
> > 



> Yes, I actually experienced HC cmos retaining stored latch states down 
> into tens of millivolts region. However to make any kind of oscillator 
> means passing slowly through a linear region and current consumption 
> will shoot up. To make an oscillator a discrete design with high value 
> series resistors might be better, this draws an average 10nA to make 
> narrow pulses every 8-9 secs...



> Version 4
> SHEET 1 1160 680
> WIRE 32 -640 -208 -640
> WIRE 336 -640 32 -640
> WIRE 864 -640 336 -640
> WIRE 336 -592 336 -640
> WIRE 32 -544 32 -640
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> SYMATTR Value 10Meg
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> WINDOW 0 0 56 VBottom 2
> WINDOW 3 32 56 VTop 2
> SYMATTR InstName R2
> SYMATTR Value 10Meg
> TEXT -242 360 Left 2 !.tran 100
> TEXT 928 336 Left 2 ;EPW SED MAY 2022
> TEXT 928 288 Left 2 ;Nano power pulser





> piglet
Reply by Piotr Wyderski ●May 14, 20222022-05-14
piglet wrote:


> Yes, I actually experienced HC cmos retaining stored latch states down 
> into tens of millivolts region. However to make any kind of oscillator 
> means passing slowly through a linear region and current consumption 
> will shoot up. To make an oscillator a discrete design with high value 
> series resistors might be better, this draws an average 10nA to make 
> narrow pulses every 8-9 secs...


Nice, your edges are super sharp. Here is mine, sort of 1us pulses at 
14Hz with 30nA average at 3V. The perhaps interesting part is the narrow 
pulse generator: the pulse duration is limited by the energy stored in 
C2, as the discharging cycle itself is orders of magnitude longer. With 
R7 I can specify any reasonable duration and it comes at no additional 
energy cost, as the energy to be dissipated has already come through R4.

On the downside, I got stuck here: no idea how to transform the 100mV 
V_OUT pulses into the full VDD swing without a fancy 100mV Vth 
transistor and still keep the average power consumption low. The bias 
network for a differential amplifier or a common base stage will burn 
hundreds of times more power than the oscillator. Inductors don't seem 
to help here.

	Best regards, Piotr


Version 4
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Reply by John S ●May 15, 20222022-05-15
On 5/14/2022 1:03 PM, piglet wrote:

> On 14/05/2022 07:04, Hul Tytus wrote:
>> Piotr&nbsp; you might look at the hc cmos series. They will operate in
>> the 1 volt range with the expected lower current. One maker spoke
>> of characterizing their devices at one something volts.
>> &nbsp;&nbsp;&nbsp; I experimented with those supply voltages for devices
>> working in the 100k cps area and all seemed pheasable.
>>
>> Hul
>>
> 
> Yes, I actually experienced HC cmos retaining stored latch states down 
> into tens of millivolts region. However to make any kind of oscillator 
> means passing slowly through a linear region and current consumption 
> will shoot up. To make an oscillator a discrete design with high value 
> series resistors might be better, this draws an average 10nA to make 
> narrow pulses every 8-9 secs...
> 
> Version 4

[Snip SPICE listing]

> piglet


Keep everything clean while building!
Reply by Piotr Wyderski ●May 22, 20222022-05-22
piglet wrote:


> To make an oscillator a discrete design with high value 
> series resistors might be better, this draws an average 10nA to make 
> narrow pulses every 8-9 secs...


After some prototyping I can confirm, your UJT-emulating circuit wins 
hands down. I removed R6, R2, Q3 and R5, changed C1 and C2 to 470p and 
coupled to the C2 discharge energy via a small transformer, getting 
beautiful 1us spikes @28Hz. Thank you, Piglet!

	Best regards, Piotr
Reply by John Larkin ●May 23, 20222022-05-23
On Sat, 14 May 2022 19:03:40 +0100, piglet <erichpwagner@hotmail.com>
wrote:


>On 14/05/2022 07:04, Hul Tytus wrote:
>> Piotr  you might look at the hc cmos series. They will operate in
>> the 1 volt range with the expected lower current. One maker spoke
>> of characterizing their devices at one something volts.
>>     I experimented with those supply voltages for devices
>> working in the 100k cps area and all seemed pheasable.
>> 
>> Hul
>> 
>
>Yes, I actually experienced HC cmos retaining stored latch states down 
>into tens of millivolts region. However to make any kind of oscillator 
>means passing slowly through a linear region and current consumption 
>will shoot up. To make an oscillator a discrete design with high value 
>series resistors might be better, this draws an average 10nA to make 
>narrow pulses every 8-9 secs...
>


I want an LED blinker to show that a high-voltage power supply is
still dangerous. It should discharge the supply at some low current
and blink from, say, 1400 volts down to maybe 40.

A variant of your circuit might work. Charge a cap through a string of
depletion fets and modify your thing with a zener between emitters.

-- 

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