BJTs as ultra low leakage protection diodes

Ebrahim wrote:
> 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
> 
   The protection diodes shown are between inputs.
   Related to inputs, note those to the substrate (V-) and if 
implemented, those to the supply are most definitely not shown.
   For both digital and analog devices, note protection diodes to the 
substrate are not shown.
   And diodes to the supply (if added) seem to be almost state secrets..

On Wed, 17 Jun 2009 01:52:59 -0700, Robert Baer
<robertbaer@localnet.com> wrote:

>Ebrahim wrote:
>> 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
>> 
>   The protection diodes shown are between inputs.
>   Related to inputs, note those to the substrate (V-) and if 
>implemented, those to the supply are most definitely not shown.
>   For both digital and analog devices, note protection diodes to the 
>substrate are not shown.
>   And diodes to the supply (if added) seem to be almost state secrets..

There's a good OP27 model on my website... one I did in the early
'90's.

                                        ...Jim Thompson
-- 
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
          Obama... Recklessness Cloaked in Righteousness