Current source [Result]

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Hi all,

According Spehro suggestion i made this :

http://dl.free.fr/vDkBbyr2N/Capture-1.png
http://dl.free.fr/o87DqeGKP/Capture-2.png

It seems that it works fine. Spehro suggest me using LMC6001 but i'm
feeling tired for the moment to implement the right model within LTspice.

it's really funny because simulation exhibits a few femtoampere into (+)
pin of each LT1012 where i expected few tens nano ...

Anyway, someone had mentioned the PCB leakage, anyone here has some
experience about ?

Best regards, Habib.

PS : I will implement Larkin ideas later.

Re: Current source [Result]
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I tried the telecharger button for both. But le fichiers don't load. Il
ne marche pas :-(

[...]

--
Regards, Joerg

http://www.analogconsultants.com /

Re: Current source [Result]
On Sun, 24 Jul 2011 09:29:00 -0700, the renowned Joerg

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Works for me, from Chicago, Fremont CA, Canada and Netherlands. Just
hit "Télécharger ce fichier"


Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: Current source [Result]
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That's what I did. Ne fonctionne pas. I guess some sort of virus or
firewall scripting block.

--
Regards, Joerg

http://www.analogconsultants.com /

Re: Current source [Result]
Le 24/07/2011 19:02, Joerg a écrit :
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Joerg

Please try those :

http://cjoint.com/?AGytkKSuTcS
http://cjoint.com/?AGytl5Orvt2


Best regards

Re: Current source [Result]
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Merci. Those work, and there's even a pretty woman above the schematic :-)

The current source could also be done with just one opamp and a low
leakage transistor. But probably you also want to switch ranges and then
you'll have to find a low leakage multiplexer or transistors. Either
expensive ones with guaranteed values or cheap ones that are tested
and/or cherry-picked. Cherry-picking isn't necessarily bad practice,
even reputable equipment manufacturers have done it.

You can still buy teflon posts, but expensive:
http://www.partsconnexion.com/solder_posts_connex.html

Also ceramic core circuit board:
http://www.bestpcbs.com/products/ceramic-pcb.htm

Not sure where you could still buy the ceramic solder strips. John
Larkin found a large quantity of them a while ago. If you buy him a beer
at Zeitgeist maybe he'll give you some :-)

--
Regards, Joerg

http://www.analogconsultants.com /

Re: Current source [Result]

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Foothill Flea Market, obviously removed from old Tek scopes.

But at 1 nA, a PCB will be fine. Just don't use water-wash flux.

John




Re: Current source [Result]
On Sun, 24 Jul 2011 16:15:37 -0700, the renowned John Larkin

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What accuracy at 1nA would you think it's fine for? 1%? 0.1%?



Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: Current source [Result]
On Sun, 24 Jul 2011 19:33:15 -0400, Spehro Pefhany

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I'd expect a clean board with a decent layout to have under 1 pA
leakage. Guarding would be a good idea if high accuracy were needed.
The output of the CMOS follower is the ideal guard drive.

If the range resistors are switched with CMOS multiplexers, they will
probably dominate the error on both the 1 nA and 1 mA ranges.

John



Re: Current source [Result]

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Why am I not surprised?  Works for me ;-)

What in the world have you done to your system to make it so... so... so...
function-proof ?:-)
 
                                       ...Jim Thompson

                  [On the Road, in New York]
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| Analog Innovations, Inc.                         |     et      |
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Re: Current source [Result]
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Some of the work I do requires certain precautions. Think of it this
way: Riding a bicycle with a helmet is uncomfortable because it can make
you sweat profusely. Riding a bicycle without a helmet can ...


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--
Regards, Joerg

[on a chair, in Cameron Park]  :-)

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Re: Current source [Result]

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Sheeeesh!
 
                                       ...Jim Thompson

                  [On the Road, in New York]
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Re: Current source [Result]
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You'd be surprised how many companies do not allow the use of certains
scripts and stuff within their premises. There's a whole slew of vendors
that misses out on sales because of that. And they will never know that
others are eating their lunch.

--
Regards, Joerg

http://www.analogconsultants.com /

Re: Current source [Result]

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I use Firefox and NoScript, yet never have the weird issues you seem to have
all the time.
 
                                       ...Jim Thompson

                  [On the Road, in New York]
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
We've slightly trimmed the long signature. Click to see the full one.
Re: Current source [Result]
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You only rely on NoScript? That would be scary ...

I never have any issues with properly designed company web sites.
Problems arise when sites want to play dicey stuff. Sometimes I come
across a not properly designed web site. The strange coincidence is that
those are companies that aren't all that important anyhow. The Digikeys
and ON-Semis of this world don't do that stuff.

--
Regards, Joerg

http://www.analogconsultants.com /

Re: Current source [Result]

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so...
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I block javascript also, except for known good sites.  At home I'm, of course,
behind a hardware firewall.  On-the-road, as I am now, I take no risks, but
also carry no risky info on the laptop.
 
                                       ...Jim Thompson

                  [On the Road, in New York]
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
We've slightly trimmed the long signature. Click to see the full one.
Re: Current source [Result]
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wrote:
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so...
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Same here. But one must be careful because eventually you will have to
work on some hot circuit even if you never store in on the HD.

But anyhoo, if a web site won't let me on unless I turn safety features
off then I will not grace it with my presence :-)

--
Regards, Joerg

http://www.analogconsultants.com /

Re: Current source [Result]
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don't work for me either

Re: Current source [Result]
On Sun, 24 Jul 2011 18:02:55 +0200, the renowned Habib

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The LT1012 has much better Vos and Vos drift specs. Bias current can
be as bad as 100pA over temperature for the most expensive grade,
which which would contribute +/-10% error on the 1nA scale. You could
use a much lower value sense resistor with the LT1012 because of the
better Vos.

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If this model is used, it should be 10s of pA, not fA or nA.

http://cds.linear.com/docs/Design%20Note/dn28.pdf

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Try to avoid the PCB entirely (eg. use a PTFE standoff for the single
critical node in your circuit (bottom end of R1/output/non inverting
input of U5). Avoid no-clean flux for the rest.

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Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
We've slightly trimmed the long signature. Click to see the full one.
Re: Current source [Result]
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[...]

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And don't let anyone smoke within a 100m radius. At least not
hand-rolled Gauloises or Gitanes Brunes without filter :-)

--
Regards, Joerg

http://www.analogconsultants.com /

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