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Any infos on µA circuits?

Alec_t

Jul 7, 2015
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Would there be a possibility to keep a similar number of components but with the output under 1v?
Simulation suggests that if R1 is increased to 1.5 Megohms, the constant current becomes 1μA and the voltage across the sample remains below 1V for all sample resistances up to 1 Megohm. [Note: I don't have a Spice model of the MAX4006. My simulation used the LTspice Universal op-amp2 model, so isn't precise].
 

Alec_t

Jul 7, 2015
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What is the maximum tissue resistance likely to be? If you must keep the voltage across the sample below 1V then the maximum resistance dictates the maximum allowable current, as per Ohm's law.

Edit: In my previous post the reference to MAX4006 should be corrected to MAX40006.
 
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hevans1944

Hop - AC8NS
Jun 21, 2012
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Often, in the scientific research community, someone will try to duplicate or replicate the work of someone else, as described in a peer-reviewed paper or a description from some other means of publication. Often "sketches on the back of paper napkins" are all anyone has to work with. I once tried to work with a chemistry professor who wanted to duplicate exactly the Wheatstone Bridge configuration described in a peer-reviewed publication. The author of the paper was not available for assistance. I could not convince the professor that the exact same bridge configuration was NOT the focus of the paper, which results he was trying to verify. He didn't know anything about electricity or electronics, but firmly believed that he had to duplicate the environment described in the original paper, right down to the type and brand of battery used to excite the Wheatstone bridge, lest he obtain results different than that described in the paper. I could not convince him otherwise, so I just explained to my supervisor what the problem was. Immediately I was removed from any responsibility to "help" this professor with his problem.

My boss was a former General Electric employee who had supervised hundreds of people at the G.E. Evendale jet engine plant near Cincinnati, Ohio. He knew people, but more importantly he knew how to manage them. I never heard any more from the professor and have no idea whether or not he was ever successful in duplicating the results of the published paper. My boss assigned me more (and more interesting) projects to work on during the the twelve years I worked there.
 

Zen_

Dec 14, 2021
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Hi,




max samples resistances values 190 - 200 kOhm (references)


Thank you again for your help.


The focus of the original study is as mentioned µA effect in tissues samples (and particular applications described in the study) and details on electrodes geometry.

Simplicity of the circuit (as implied), portability and the mention of "button cell" (without details in notes) is the chosen methodology of the study (it is mentioned that this was chosen after several test).

While not being the focus per say, the replication of the circuit, can provide informations (be it for duplication or as addendum for experimental and/or historical purpose) on the original study.

Duplication of this particular study would involve similar parameters, however studying this subject can done with a different approach (and configuration)

While looking for published references of similar studies, similar emphasis is found as the one discussed on electrodes geometry but no details on constant current values and basic tissues resistance data (If constant µA is of importance, this is not the focus)

Replication of the study is possible while only being concerned about constant µA and output voltage under 1.1v.

Without constraints of a button cell and relative portability of battery (any type) or number of components only focusing on the constant values, what would be the easiest configuration?
 
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Zen_

Dec 14, 2021
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The example provided by Alec_t is the closest to the study (taking all consideration into account)


I do understand that the focus and primary objective is in fine the replication of a study, when there are no references other than the present work, this complicate the matter further.

If the configuration is not the focus and any circuit producing similar output is valid then clearly the original configuration is not the issue.

If there is a reasoning (portability, constraint due to external factors, temperatures or stability) who are taken into account then there is a reason to at least duplicate as closely as possible with a similar configuration.

Only focusing on µA circuits published there are example (from current limiting diodes such as j500, DC- DC controller with adjustable constant current) The issue in this case is voltage values and deviations.

"the constant current becomes 1μA and the voltage across the sample remains below 1V for all sample resistances up to 1 Megohm." This is exactly the answer.

A few patents discuss the issue of skin impedance (in vivo in this case but in vitro tissues depending on state of tissues can have a wide range of values as data indicate)

There is a patent that focus on DC - DC converter to ensure that the controller circuit avoid voltage drop and current regulation.

The controller circuit in this case is described as: series pass regulator comprising MOSFET transistor, resistors, capacitor and operational amplifier.

iu
 

Zen_

Dec 14, 2021
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I already mentioned that the circuit provided by Alec_t is the closest answer provided.

Let me know if you can be credited as Alec_t, having provided details on the duplication of the original configuration.

The original thread question is answered.


My own question (not pertaining to the original study details per say) is simply without the challenging battery constraint, what would be the easiest way to have similar output.

I simply looked at available data and if anything was of interest.
 
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Alec_t

Jul 7, 2015
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Let me know if you can be credited as Alec_t, having provided details on the duplication of the original configuration.
The circuit I provided is a standard constant-current configuration. Nothing novel apart from the choice of components to try to meet the low current and small size conditions.
My own question (not pertaining to the original study details per say) is simply without the challenging battery constraint, what would be the easiest way to have similar output.
I doubt there is anything easier. Instead of a button cell you could use a couple of AAcells, but even a small button cell should suffice for a long run time.
 

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