NPN protective zener

[Winfield Hill]

John Larkin wrote...

On 24 Jun 2019, Phil Hobbs wrote:

The beta loss is indicative of progressive junction
damage, which is what would make me nervous about
this idea. Sounds like a long-term reliability
headache.

I ran a small NPN as a b-e zener for a week or so.
The voltage declined a bit, roughly 1% as I recall,
and seemed to be leveling out.

The "zener" effect we're using is actually the
avalanche effect, which has quite robust physics,
and doesn't use any of the usual BJT mechanisms.
Except for inverted-mode beta at high currents.
That could cause a small change in zener voltage.
I'm looking forward to doing some long-term tests.


--
Thanks,
- Win

 

[Winfield Hill]

Phil Hobbs wrote...

But probably not with recurrent ampere-level pulses.
Some things are too far out on the lunatic fringe
even for you.

John has the equipment, and is up for such a test.
Me too, I'm going to do 1A and 10A repetitive tests,
even if that seems a bit unrealistic, for typical
applications.


--
Thanks,
- Win

 

[Phil Hobbs]

On 6/24/19 3:42 PM, John Larkin wrote:

On Mon, 24 Jun 2019 14:01:51 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/23/19 11:43 AM, mixed nuts wrote:
On 6/22/2019 1:58 PM, Winfield Hill wrote:
mixed nuts wrote...

Low noise transistors become noisy transistors after the b-e
junction has been zenered a few times. I didn't have an
opportunity to do a rigorous before-after gain comparison but it
didn't seem to change dramatically.

Others have observed a serious loss in beta. There are rumors of
ways to resurrect the poor beast, but if its role in life is as a
low-capacitance zener clamp, who cares? When it's wired up on a
PCB, with the base and collector shorted, there's little else that
it could ever do!

Just don't put them back in the drawer after you finish playing.



The beta loss is indicative of progressive junction damage, which is
what would make me nervous about this idea. Sounds like a long-term
reliability headache.

Cheers

Phil Hobbs

I ran a small NPN as a b-e zener for a week or so. The voltage
declined a bit, roughly 1% as I recall, and seemed to be leveling out.

But probably not with recurrent ampere-level pulses. Some things are too
far out on the lunatic fringe even for you.

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

 

[Phil Hobbs]

On 6/24/19 3:40 PM, John Larkin wrote:

On Mon, 24 Jun 2019 12:13:09 -0700 (PDT), pcdhobbs@gmail.com wrote:

I'd love to get semiconductor CV curves easily. The SMU would need two
channels that can also measure capacitance.

Wire a couple of Boonton 72s in series with the SMUs!

Cheers

Phil Hobbs

Yes, they have bias inputs on the back. Where's the Ethernet
connector?

Didn't one of the Boontons have BCD out?

They have analogue voltage outputs, n'est ce pas? A LabJack is good
medicine for that sort of job.

The 72BD has BCD outputs as well IIRC, but I've never used them.

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

 

[Phil Hobbs]

On 6/21/19 8:09 PM, George Herold wrote:

On Friday, June 21, 2019 at 11:00:24 AM UTC-4, John Larkin wrote:
On 21 Jun 2019 03:05:47 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

This is the paragraph I'm adding, as a
footnote to the graph in the x-Chapter
section on protection devices:

"The reverse avalanche breakdown of the 2N3904
is very sharp, with no current conducted at all
below 7 volts. Once it starts conducting, it
has a low dynamic resistance, with the breakdown
voltage increasing only 5mV / decade up to 1mA,
where its resistance is about 5 ohms. The
voltage increases by a volt at 100mA, and its
still about 5 ohms. We get only one more volt
by 0.5A, where the resistance is even lower.
Above 50mA the breakdown voltage will be a
little higher if you leave the collector pin
open, you need it connected to benefit from
its assistance with inverted-mode gain. The
2N3904 is fine carrying very high currents,
protecting your fragile devices, if the time
is short enough. It's worth noting that the
r_bb' base-resistance we measured and reported
in Table 8.1a, which was 110 ohms for the
2N3904, is not relevant to the breakdown."

I'm hoping that by the time the book goes to
print, I'll have replaced the graph with one
that goes to 10A. I'm confidant the 2N3904,
as with most other zener (actually avalanche)
devices, can handle full 10A peak currents in
the 8-20us surge tests, and pass. So it's a
totally viable low-capacitance protection device.

If one gets it in the SC-70 SOT-323 package
(at least four manufacturers*), it's not even
that large (I still prefer diode-package parts).
Fairchild offers a dual 2N3904 in an SC-70-6
package, FFB3904.** Huge stocking levels and
low prices, too, for all of these.
Lots of interest. Amazing, who knew?

* ON Semi MMBT3904WT1G, Diodes MMST3904-7-F,
Nexperia PMSS3904, MCC MMST3904-TP.

** and the FMB3946, get one each 2n3904 and
2n3906 in SC-70-6, and other manuf as well.


BFT25 is a phenomenal diode:

https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

The low end was limited by my measurement rig and may be even better.
Huh, can you say anything about the measurement rig.
(610 electrometer?)
I've measured current of about a pA with a ~10 pA bias current opamp
(difference measurement...

I think I was looking at c-b junction of a ~200V npn.
'HV' diode with low leakage.

The Keithley 610 is a pretty good instrument. Its bottom range is 10 fA
FS, which is more aspirational than functional, but the 100 fA range is
pretty solid, considering.

Some modern CMOS op amps will blow the 610 into the weeds.

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

 

[John Larkin]

On Mon, 24 Jun 2019 21:29:58 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/21/19 8:09 PM, George Herold wrote:
On Friday, June 21, 2019 at 11:00:24 AM UTC-4, John Larkin wrote:
On 21 Jun 2019 03:05:47 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

This is the paragraph I'm adding, as a
footnote to the graph in the x-Chapter
section on protection devices:

"The reverse avalanche breakdown of the 2N3904
is very sharp, with no current conducted at all
below 7 volts. Once it starts conducting, it
has a low dynamic resistance, with the breakdown
voltage increasing only 5mV / decade up to 1mA,
where its resistance is about 5 ohms. The
voltage increases by a volt at 100mA, and its
still about 5 ohms. We get only one more volt
by 0.5A, where the resistance is even lower.
Above 50mA the breakdown voltage will be a
little higher if you leave the collector pin
open, you need it connected to benefit from
its assistance with inverted-mode gain. The
2N3904 is fine carrying very high currents,
protecting your fragile devices, if the time
is short enough. It's worth noting that the
r_bb' base-resistance we measured and reported
in Table 8.1a, which was 110 ohms for the
2N3904, is not relevant to the breakdown."

I'm hoping that by the time the book goes to
print, I'll have replaced the graph with one
that goes to 10A. I'm confidant the 2N3904,
as with most other zener (actually avalanche)
devices, can handle full 10A peak currents in
the 8-20us surge tests, and pass. So it's a
totally viable low-capacitance protection device.

If one gets it in the SC-70 SOT-323 package
(at least four manufacturers*), it's not even
that large (I still prefer diode-package parts).
Fairchild offers a dual 2N3904 in an SC-70-6
package, FFB3904.** Huge stocking levels and
low prices, too, for all of these.
Lots of interest. Amazing, who knew?

* ON Semi MMBT3904WT1G, Diodes MMST3904-7-F,
Nexperia PMSS3904, MCC MMST3904-TP.

** and the FMB3946, get one each 2n3904 and
2n3906 in SC-70-6, and other manuf as well.


BFT25 is a phenomenal diode:

https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

The low end was limited by my measurement rig and may be even better.
Huh, can you say anything about the measurement rig.
(610 electrometer?)
I've measured current of about a pA with a ~10 pA bias current opamp
(difference measurement...

I think I was looking at c-b junction of a ~200V npn.
'HV' diode with low leakage.

The Keithley 610 is a pretty good instrument. Its bottom range is 10 fA
FS, which is more aspirational than functional, but the 100 fA range is
pretty solid, considering.

Some modern CMOS op amps will blow the 610 into the weeds.

Cheers

Phil Hobbs

My capacitor charging thing could get well into the aA range. I just
need a good SPDT switch.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Michael Terrell]

On Monday, June 24, 2019 at 3:43:26 PM UTC-4, John Larkin wrote:

On Mon, 24 Jun 2019 12:13:09 -0700 (PDT), Phil Hobbs wrote:

I'd love to get semiconductor CV curves easily. The SMU would need two
channels that can also measure capacitance.

Wire a couple of Boonton 72s in series with the SMUs!

Cheers

Phil Hobbs

Yes, they have bias inputs on the back. Where's the Ethernet
connector?

Didn't one of the Boontons have BCD out?

The Boonton 72AD has BCD outputs.


https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwjOwqCgwIPjAhUwT98KHUTfDyIQIDAAegQIBRAF&url=http%3A%2F%2Fwebcache.googleusercontent.com%2Fsearch%3Fq%3Dcache%3AGe_g4Me3fOcJ%3Amanuals.repeater-builder.com%2Fte-files%2FBOONTON%2FBOONTON%25252072AD%252520Instructions.pdf%2B%26cd%3D1%26hl%3Den%26ct%3Dclnk%26gl%3Dus%26client%3Dfirefox-b-1-d&usg=AOvVaw1SvaY7QEnVS2LGeTJG0Sl0


The 7200 series has IEEE-488 interface for automated testing

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwipuqOaw4PjAhXCm-AKHeXnBFwQIDAAegQIABAE&url=https%3A%2F%2Fwebcache.googleusercontent.com%2Fsearch%3Fq%3Dcache%3AMuGL71pPMCsJ%3Ahttps%3A%2F%2Fboonton.com%2Ftestpages%2Flegacy-products%2F7200-capacitance-meter%253Fgo%253Dmanuals_software%2B%26cd%3D1%26hl%3Den%26ct%3Dclnk%26gl%3Dus%26client%3Dfirefox-b-1-d&usg=AOvVaw2mwYretIyH3WQKvXcT5xKo

I don't have either of these, but I do have the 42, 92, 4200 and 9200 series meters. The older analog models allow remote range selection, but do not have an A/D converter. Only those ending in D have these, in their two number model series.

 

On Tuesday, 25 June 2019 03:28:50 UTC+1, John Larkin wrote:

On Mon, 24 Jun 2019 21:29:58 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
On 6/21/19 8:09 PM, George Herold wrote:
On Friday, June 21, 2019 at 11:00:24 AM UTC-4, John Larkin wrote:

https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

The low end was limited by my measurement rig and may be even better.

Huh, can you say anything about the measurement rig.
(610 electrometer?)
I've measured current of about a pA with a ~10 pA bias current opamp
(difference measurement...

I think I was looking at c-b junction of a ~200V npn.
'HV' diode with low leakage.

The Keithley 610 is a pretty good instrument. Its bottom range is 10 fA
FS, which is more aspirational than functional, but the 100 fA range is
pretty solid, considering.

Some modern CMOS op amps will blow the 610 into the weeds.

Cheers

Phil Hobbs

My capacitor charging thing could get well into the aA range. I just
need a good SPDT switch.

Dracula's knife switch would at least give lots of clearance.


NT

 

[John Larkin]

On 24 Jun 2019 18:19:48 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

Phil Hobbs wrote...

But probably not with recurrent ampere-level pulses.
Some things are too far out on the lunatic fringe
even for you.

John has the equipment, and is up for such a test.
Me too, I'm going to do 1A and 10A repetitive tests,
even if that seems a bit unrealistic, for typical
applications.

10 amps is easy, just a pulse generator and a mosfet. Put a resistor
in the mosfet source for constant-current pulsing.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Mon, 24 Jun 2019 21:08:46 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/24/19 3:42 PM, John Larkin wrote:
On Mon, 24 Jun 2019 14:01:51 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/23/19 11:43 AM, mixed nuts wrote:
On 6/22/2019 1:58 PM, Winfield Hill wrote:
mixed nuts wrote...

Low noise transistors become noisy transistors after the b-e
junction has been zenered a few times. I didn't have an
opportunity to do a rigorous before-after gain comparison but it
didn't seem to change dramatically.

Others have observed a serious loss in beta. There are rumors of
ways to resurrect the poor beast, but if its role in life is as a
low-capacitance zener clamp, who cares? When it's wired up on a
PCB, with the base and collector shorted, there's little else that
it could ever do!

Just don't put them back in the drawer after you finish playing.



The beta loss is indicative of progressive junction damage, which is
what would make me nervous about this idea. Sounds like a long-term
reliability headache.

Cheers

Phil Hobbs

I ran a small NPN as a b-e zener for a week or so. The voltage
declined a bit, roughly 1% as I recall, and seemed to be leveling out.


But probably not with recurrent ampere-level pulses. Some things are too
far out on the lunatic fringe even for you.

Cheers

Phil Hobbs

Not with my safety glasses.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Dave Platt]

In article <dfc2fa60-efca-4637-80ee-cf56dda879f5@googlegroups.com>,
<tabbypurr@gmail.com> wrote:

My capacitor charging thing could get well into the aA range. I just
need a good SPDT switch.

Dracula's knife switch would at least give lots of clearance.

Wasn't it Dr. Frankenstein who had the big knife-switch?

And, if I recall correctly, that switch was always festooned with
cobwebs. This might create paths for excessive leakage, especially if
the weather is damp (which it usually was during the doctor's normal
work hours... something about thunderstorms...)

 

[George Herold]

On Tuesday, June 25, 2019 at 3:16:46 PM UTC-4, John Larkin wrote:

On Tue, 25 Jun 2019 14:56:21 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/25/19 9:39 AM, tabbypurr@gmail.com wrote:
On Tuesday, 25 June 2019 03:28:50 UTC+1, John Larkin wrote:
On Mon, 24 Jun 2019 21:29:58 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
On 6/21/19 8:09 PM, George Herold wrote:
On Friday, June 21, 2019 at 11:00:24 AM UTC-4, John Larkin wrote:

https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

The low end was limited by my measurement rig and may be even better.

Huh, can you say anything about the measurement rig.
(610 electrometer?)
I've measured current of about a pA with a ~10 pA bias current opamp
(difference measurement...

I think I was looking at c-b junction of a ~200V npn.
'HV' diode with low leakage.

The Keithley 610 is a pretty good instrument. Its bottom range is 10 fA
FS, which is more aspirational than functional, but the 100 fA range is
pretty solid, considering.

Some modern CMOS op amps will blow the 610 into the weeds.

Cheers

Phil Hobbs

My capacitor charging thing could get well into the aA range. I just
need a good SPDT switch.

Dracula's knife switch would at least give lots of clearance.


NT


Were his teeth bolted on?

Cheers

Phil Hobbs

(I suspect you meant Frankenstein.)


Only one side of one switch needs really low leakage.

https://www.dropbox.com/s/vj47r3uw9f3klm8/aA_Tester.JPG?raw=1

What's S1 for? (S2 resets cap and measures offset V.)
George H.

That probably needs some home-made switch.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Tue, 25 Jun 2019 11:27:30 -0700, dplatt@coop.radagast.org (Dave
Platt) wrote:

In article <dfc2fa60-efca-4637-80ee-cf56dda879f5@googlegroups.com>,
tabbypurr@gmail.com> wrote:

My capacitor charging thing could get well into the aA range. I just
need a good SPDT switch.

Dracula's knife switch would at least give lots of clearance.

Wasn't it Dr. Frankenstein who had the big knife-switch?

And, if I recall correctly, that switch was always festooned with
cobwebs. This might create paths for excessive leakage, especially if
the weather is damp (which it usually was during the doctor's normal
work hours... something about thunderstorms...)

A small antenna and a high-z voltmeter does interesting things as a
cloud passes over. A lightning shot can really change the e-field.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Tue, 25 Jun 2019 14:56:21 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/25/19 9:39 AM, tabbypurr@gmail.com wrote:
On Tuesday, 25 June 2019 03:28:50 UTC+1, John Larkin wrote:
On Mon, 24 Jun 2019 21:29:58 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
On 6/21/19 8:09 PM, George Herold wrote:
On Friday, June 21, 2019 at 11:00:24 AM UTC-4, John Larkin wrote:

https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

The low end was limited by my measurement rig and may be even better.

Huh, can you say anything about the measurement rig.
(610 electrometer?)
I've measured current of about a pA with a ~10 pA bias current opamp
(difference measurement...

I think I was looking at c-b junction of a ~200V npn.
'HV' diode with low leakage.

The Keithley 610 is a pretty good instrument. Its bottom range is 10 fA
FS, which is more aspirational than functional, but the 100 fA range is
pretty solid, considering.

Some modern CMOS op amps will blow the 610 into the weeds.

Cheers

Phil Hobbs

My capacitor charging thing could get well into the aA range. I just
need a good SPDT switch.

Dracula's knife switch would at least give lots of clearance.


NT


Were his teeth bolted on?

Cheers

Phil Hobbs

(I suspect you meant Frankenstein.)

Only one side of one switch needs really low leakage.

https://www.dropbox.com/s/vj47r3uw9f3klm8/aA_Tester.JPG?raw=1


That probably needs some home-made switch.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Phil Hobbs]

On 6/25/19 9:39 AM, tabbypurr@gmail.com wrote:

On Tuesday, 25 June 2019 03:28:50 UTC+1, John Larkin wrote:
On Mon, 24 Jun 2019 21:29:58 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
On 6/21/19 8:09 PM, George Herold wrote:
On Friday, June 21, 2019 at 11:00:24 AM UTC-4, John Larkin wrote:

https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

The low end was limited by my measurement rig and may be even better.

Huh, can you say anything about the measurement rig.
(610 electrometer?)
I've measured current of about a pA with a ~10 pA bias current opamp
(difference measurement...

I think I was looking at c-b junction of a ~200V npn.
'HV' diode with low leakage.

The Keithley 610 is a pretty good instrument. Its bottom range is 10 fA
FS, which is more aspirational than functional, but the 100 fA range is
pretty solid, considering.

Some modern CMOS op amps will blow the 610 into the weeds.

Cheers

Phil Hobbs

My capacitor charging thing could get well into the aA range. I just
need a good SPDT switch.

Dracula's knife switch would at least give lots of clearance.


NT

Were his teeth bolted on?

Cheers

Phil Hobbs

(I suspect you meant Frankenstein.)

--
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

 

On Tuesday, 25 June 2019 20:08:07 UTC+1, Dave Platt wrote:

In article <dfc2fa60-efca-4637-80ee-cf56dda879f5@googlegroups.com>,
tabbypurr> wrote:

My capacitor charging thing could get well into the aA range. I just
need a good SPDT switch.

Dracula's knife switch would at least give lots of clearance.

Wasn't it Dr. Frankenstein who had the big knife-switch?

they were both the same era, but IIRC Dracula had not yet modernised to getting electricity.

And, if I recall correctly, that switch was always festooned with
cobwebs. This might create paths for excessive leakage, especially if
the weather is damp (which it usually was during the doctor's normal
work hours... something about thunderstorms...)

Yes, some aspects I think one could improve on, including the ebonite. Once you've picked your materials, a knife switch could be a good format.

If one were willing to go to vacuum, springy metal in a vacuum could be used, rotate the container to switch it.


NT

 

[Phil Hobbs]

On 6/25/19 5:01 PM, John Larkin wrote:

On Tue, 25 Jun 2019 12:24:31 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Tuesday, June 25, 2019 at 3:16:46 PM UTC-4, John Larkin wrote:
On Tue, 25 Jun 2019 14:56:21 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/25/19 9:39 AM, tabbypurr@gmail.com wrote:
On Tuesday, 25 June 2019 03:28:50 UTC+1, John Larkin wrote:
On Mon, 24 Jun 2019 21:29:58 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
On 6/21/19 8:09 PM, George Herold wrote:
On Friday, June 21, 2019 at 11:00:24 AM UTC-4, John Larkin wrote:

https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

The low end was limited by my measurement rig and may be even better.

Huh, can you say anything about the measurement rig.
(610 electrometer?)
I've measured current of about a pA with a ~10 pA bias current opamp
(difference measurement...

I think I was looking at c-b junction of a ~200V npn.
'HV' diode with low leakage.

The Keithley 610 is a pretty good instrument. Its bottom range is 10 fA
FS, which is more aspirational than functional, but the 100 fA range is
pretty solid, considering.

Some modern CMOS op amps will blow the 610 into the weeds.

Cheers

Phil Hobbs

My capacitor charging thing could get well into the aA range. I just
need a good SPDT switch.

Dracula's knife switch would at least give lots of clearance.


NT


Were his teeth bolted on?

Cheers

Phil Hobbs

(I suspect you meant Frankenstein.)


Only one side of one switch needs really low leakage.

https://www.dropbox.com/s/vj47r3uw9f3klm8/aA_Tester.JPG?raw=1

What's S1 for? (S2 resets cap and measures offset V.)
George H.


S1 isolates the integrating node from the opamp input current.

S2 ground-checks the opamp, to measure offset.

Pushing both discharges the cap.

How would we test this? The biggest resistor that I have is 1T. 1 volt
across that is 1,000,000 aA.

Just charging up its ~50 fF capacitance to 1V takes 50,000 aC.

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

 

[John Larkin]

On Tue, 25 Jun 2019 12:24:31 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Tuesday, June 25, 2019 at 3:16:46 PM UTC-4, John Larkin wrote:
On Tue, 25 Jun 2019 14:56:21 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/25/19 9:39 AM, tabbypurr@gmail.com wrote:
On Tuesday, 25 June 2019 03:28:50 UTC+1, John Larkin wrote:
On Mon, 24 Jun 2019 21:29:58 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
On 6/21/19 8:09 PM, George Herold wrote:
On Friday, June 21, 2019 at 11:00:24 AM UTC-4, John Larkin wrote:

https://www.dropbox.com/s/ft0tsikhdi90rgq/BFT25.JPG?raw=1

The low end was limited by my measurement rig and may be even better.

Huh, can you say anything about the measurement rig.
(610 electrometer?)
I've measured current of about a pA with a ~10 pA bias current opamp
(difference measurement...

I think I was looking at c-b junction of a ~200V npn.
'HV' diode with low leakage.

The Keithley 610 is a pretty good instrument. Its bottom range is 10 fA
FS, which is more aspirational than functional, but the 100 fA range is
pretty solid, considering.

Some modern CMOS op amps will blow the 610 into the weeds.

Cheers

Phil Hobbs

My capacitor charging thing could get well into the aA range. I just
need a good SPDT switch.

Dracula's knife switch would at least give lots of clearance.


NT


Were his teeth bolted on?

Cheers

Phil Hobbs

(I suspect you meant Frankenstein.)


Only one side of one switch needs really low leakage.

https://www.dropbox.com/s/vj47r3uw9f3klm8/aA_Tester.JPG?raw=1

What's S1 for? (S2 resets cap and measures offset V.)
George H.

S1 isolates the integrating node from the opamp input current.

S2 ground-checks the opamp, to measure offset.

Pushing both discharges the cap.

How would we test this? The biggest resistor that I have is 1T. 1 volt
across that is 1,000,000 aA.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[whit3rd]

On Tuesday, June 25, 2019 at 12:16:46 PM UTC-7, John Larkin wrote:

On 6/25/19 9:39 AM, tabbypurr@gmail.com wrote:

[Doctor Frankenstein's][ knife switch would at least give lots of clearance.

Only one side of one switch needs really low leakage.

That probably needs some home-made switch.

Mercury tilt switch, perhaps?
Lots of the reed-switch relays of yesteryear had good insulation standoff
distances, with dry inert atmosphere fill.

 

[John Larkin]

On Tue, 25 Jun 2019 17:36:45 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Tuesday, June 25, 2019 at 12:16:46 PM UTC-7, John Larkin wrote:

On 6/25/19 9:39 AM, tabbypurr@gmail.com wrote:

[Doctor Frankenstein's][ knife switch would at least give lots of clearance.

Only one side of one switch needs really low leakage.

That probably needs some home-made switch.

Mercury tilt switch, perhaps?
Lots of the reed-switch relays of yesteryear had good insulation standoff
distances, with dry inert atmosphere fill.

A reed might be OK, activated by a magnet.

Some simple mechanical thing would be better. Air is a good insulator.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com