BJTs as ultra low leakage protection diodes

On Sat, 13 Jun 2009 21:48:27 +0430, Ebrahim <Engineer.Ebi@gmail.com>
wrote:

>Phil Hobbs wrote:
>> Ebrahim wrote:
>
>> What op amp have you ever seen that didn't, and how do you know?  Such a 
>> device might be quite interesting in applications, but I don't know of one.
> > Even femtoamp leakage devices (e.g. the venerable LMC660) have
> > protection diodes.  You can use them for resetting integrators, by
> > briefly inverting the power rails (with suitable current limits).  Win
> > Hill posted a circuit for that in this very group a few years back.
> >
>***
>Hello Phil
>
>Look at data sheet of OPA627, It has shown equivalent schematic. I do 
>not see any protection diodes in inputs.
>

An ohmmeter will tell. If it has them, all you need to do is limit the
current.

If not, use the c-b junctions of a BFT25.

John

Ebrahim wrote:
> Robert Baer wrote:
> 
>>   In a way i have "measured" leakage current in LEDs; low microamps 
>> for remaining visibility which i think is astounding, and <1nA in the 
>> 1V (forward) region with corresponding reverse values.
>>   Certainly not in the region you want.
> 
> Wow, uA and nA :-o !
> then they can't be used as an ultra low leakage. Even humble 1N4148 has 
> lower leakage ;) .
   OK; just did some "reasonable" measurements with the Everlight super 
bright LED EL-334-15/T2C2-1TVB:
<3nA @4V reverse (seems linear from 0 at 0V to there and then tends to 
curve up near 4.5V); <400nA forward.
   A bit light sensitive either way; no bright lighting on it.

   Maybe for picoamps at low capacitance try various NPN and PNP 
transistors; E-B and C-B junctions.

Joerg wrote:
> Robert Baer wrote:
>> Ebrahim wrote:
>>> Robert Baer wrote:
>>>> Ebrahim wrote:
>>>>> Hello, I want is there anyone that has used a BJT instead of ultra 
>>>>> low leakage diode(<10pA) in a serious design. The reason that I do 
>>>>> not use JFET is that I need high breakdown(100V) voltage. So I also 
>>>>> need Bootstrapping  I have down some measurements with different 
>>>>> JFETs and BJTs and I didn't find quite big differences.
>>>>   Do not think BJTs in general are that good; try an LED...
>>>
>>>
>>>
>>> Hello Robert :)
>>> Thanks for replying to my post. The main problem with LEDs is their 
>>> low breakdown voltage. I have not measured leakage current of an LED 
>>> but it makes sense because GaAs Reverse saturation current is about 
>>> 10 times less than Si. Have you used LED as an ultra low leakage 
>>> diode ? have you measured leakage currents of LEDs?
>>>
>>> Regards,
>>> Ebrahim
>>   In a way i have "measured" leakage current in LEDs; low microamps 
>> for remaining visibility which i think is astounding, and <1nA in the 
>> 1V (forward) region with corresponding reverse values.
>>   Certainly not in the region you want.
> 
> 
> Nanoamps? Wow. Is that spec'd anywhere? If so then they'd be really 
> useful as limiters.
> 
   LEDs have no spec for leakage; just set up a fixture in low lighting 
conditions and test to what is reasonable like i did (4V or less in 
reverse); see response posted a bit earlier.

Phil Hobbs wrote:
> Ebrahim wrote:
>> Robert Baer wrote:
>>> Ebrahim wrote:
>>>   Do not think BJTs in general are that good; try an LED...
>>
>> Hello Robert  :)
>> Thanks for replying to my post. I have not measured leakage current of 
>> an LED but it makes sense because GaAs Reverse saturation current is 
>> about 10 times less than Si. Have you used LED as an ultra low leakage 
>> diode ? have you measured leakage currents of LEDs?
>>
>> Regards,
>> Ebrahim
> 
> It's far lower than that.  I've measured ordinary red display LEDs whose 
> leakage was below 100 fA from -5V to +0.5V bias.
> 
> Cheers
> 
> Phil Hobbs
> 
   Hah!
   That shows red LEDs to be far superior to white ones (where i got 
<3nA @ 4V reverse); the "cost" prolly means that it must be protected 
from all ambient light.

Phil Allison wrote:
> "Ebrahim"
> 
> "Ebrahim"
> 
> 
> ** You are a totally stupid pile of autistic shit, a waste of space a waster
> of good people's valuable time.
> 
>    Fuck off and DROP DEAD  !!!
> 
> 
> 
> 
> 
> 
   You are worse than i am...at least i "took the hint" and have stopped 
posting stuff from investment newsletters...

Robert Baer wrote:
> Phil Hobbs wrote:
>> Ebrahim wrote:
>>> Robert Baer wrote:
>>>> Ebrahim wrote:
>>>>   Do not think BJTs in general are that good; try an LED...
>>>
>>> Hello Robert  :)
>>> Thanks for replying to my post. I have not measured leakage current 
>>> of an LED but it makes sense because GaAs Reverse saturation current 
>>> is about 10 times less than Si. Have you used LED as an ultra low 
>>> leakage diode ? have you measured leakage currents of LEDs?
>>>
>>> Regards,
>>> Ebrahim
>>
>> It's far lower than that.  I've measured ordinary red display LEDs 
>> whose leakage was below 100 fA from -5V to +0.5V bias.
>>
>> Cheers
>>
>> Phil Hobbs
>>
>   Hah!
>   That shows red LEDs to be far superior to white ones (where i got <3nA 
> @ 4V reverse); the "cost" prolly means that it must be protected from 
> all ambient light.

White LEDs are made of GaN--not the world's greatest semiconductor.

Cheers

Phil Hobbs

Ebrahim wrote:
> Phil Hobbs wrote:
>> Ebrahim wrote:
> 
>> What op amp have you ever seen that didn't, and how do you know?  Such 
>> a device might be quite interesting in applications, but I don't know 
>> of one.
>  > Even femtoamp leakage devices (e.g. the venerable LMC660) have
>  > protection diodes.  You can use them for resetting integrators, by
>  > briefly inverting the power rails (with suitable current limits).  Win
>  > Hill posted a circuit for that in this very group a few years back.
>  >
> ***
> Hello Phil
> 
> Look at data sheet of OPA627, It has shown equivalent schematic. I do 
> not see any protection diodes in inputs.
* "Equivalent schematics" AFAIK have never shown protection diodes, and 
in many cases will imply possible operation in regions that just cannot 
be achieved with a real device.
   Almost all analog and digital devices have a reverse polarity 
protection diode "built in" under the bonding pad and many have the same 
at the outputs; this appears to be standard practice and is ASS-u-ME-ed 
known and therefore not alluded to by most people in the industry.
   In a number of cases, an additional diode may be added to the supply 
rail and/or the doping of the pad-diode may be adjusted for a (say) 
zener breakdown of 5-8V.
   Cannot say about that as i have not tried to measure this presumption 
- and again industry is fairly quiet..

> 
> 
>> There are folks here who post stuff that's way beyond their 
>> competence...you've been here long enough to know who some of them 
>> are.  Joining that group isn't necessarily the best way to achieve 
>> respect.  Just saying.
> 
> I really do not understand what you are talking about.
> I'm not here to join some internal groups, I'm not here to woo members.
> I'm not aware of factions of this newsgroup and honestly I do not care 
> about them if they exist. I'm here to discuss technical issues. I never 
> claim something that I'm not. I ask questions and if I know something 
> about a topic I post my opinion. If someone provided documents and 
> proved that I'm wrong about something, then I learn from him and thank 
> him, provided that he present his reasons politely and respectfully.
> I do not remember I've claimed anything here. so your post really 
> surprised me.
> 
> regards,
> Ebrahim
> 
> 

Robert Baer wrote:

> * "Equivalent schematics" AFAIK have never shown protection diodes, and 
> in many cases will imply possible operation in regions that just cannot 
> be achieved with a real device.
>   Almost all analog and digital devices have a reverse polarity 
> protection diode "built in" under the bonding pad and many have the same 
> at the outputs; this appears to be standard practice and is ASS-u-ME-ed 
> known and therefore not alluded to by most people in the industry.
>   In a number of cases, an additional diode may be added to the supply 
> rail and/or the doping of the pad-diode may be adjusted for a (say) 
> zener breakdown of 5-8V.
>   Cannot say about that as i have not tried to measure this presumption 
> - and again industry is fairly quiet..
***
Robert:
  They do look at Op27 
datasheet(http://www.analog.com/en/other/militaryaerospace/op27/products/product.html) 
it also has shown equivalent schematics. I can show you many BJT opamp 
that have shown protection diodes and also can show you many ultra low 
bias current opamps without protection.

If it is assumed to be known there should be some references to show 
that can prove this. I couldn't have find one. I'm not expecting you to 
show me a reference but I expect people that accuse me of "going beyond 
competence" just because I posted something that I assume is true to 
provide references to back their claims. I have provided my references: 
2 datasheets op27 and opa627(I can post many more).

Regards,
Ebrahim

Phil Hobbs wrote:
> Robert Baer wrote:
>> Phil Hobbs wrote:
>>> Ebrahim wrote:
>>>> Robert Baer wrote:
>>>>> Ebrahim wrote:
>>>>>   Do not think BJTs in general are that good; try an LED...
>>>>
>>>> Hello Robert  :)
>>>> Thanks for replying to my post. I have not measured leakage current 
>>>> of an LED but it makes sense because GaAs Reverse saturation current 
>>>> is about 10 times less than Si. Have you used LED as an ultra low 
>>>> leakage diode ? have you measured leakage currents of LEDs?
>>>>
>>>> Regards,
>>>> Ebrahim
>>>
>>> It's far lower than that.  I've measured ordinary red display LEDs 
>>> whose leakage was below 100 fA from -5V to +0.5V bias.
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>>
>>   Hah!
>>   That shows red LEDs to be far superior to white ones (where i got 
>> <3nA @ 4V reverse); the "cost" prolly means that it must be protected 
>> from all ambient light.
> 
> White LEDs are made of GaN--not the world's greatest semiconductor.
> 
> Cheers
> 
> Phil Hobbs
   Sorry; that is all i had for testing.

On Jun 12, 10:35=A0pm, Ebrahim <Engineer....@gmail.com> wrote:
> m...@sushi.com wrote:
> > What exactly are you trying to protect? IC, fet, ??
>
> Hello,
> I'm =A0Trying to protect input of Ultra low bias current FET OpAmps.
>
> Regards,
> Ebrahim

Getting back to the basic question, breakdown voltages are only
guaranteed at a minimum. Suppose you get a device that has exceedingly
good breakdown?