how mesure low current variation

[Nik_Henri]

Hi,
first of all thank you for your interest in my problem.

I need to read the current variation and i would like to be able to read a variation as small as 1uA.
I know that there are alot of current sensing product but the problem is that my load use about 70mA (120mA max) and would like to be able to see the difference between 70mA and 70.001mA. Is there a way to subtract current or voltage with high precision ? If i could remove 70mA i would get a much better resolution:roll:.

Thank you

-Nik-

 

[Mehrshad74]

your problem is not clear:
1-do you want to detect 1uA variation of the average current? if so what is the uA/sec value?
2-do you want to measure(or detect) the difference of the current and a 70.000mA reference?
3-What is the Max acceptable drop on the shunt resistor?

 

[Nik_Henri]

1-do you want to detect 1uA variation of the average current? if so what is the uA/sec value?
Yes, i want to detect a 1uA variation of the average current. The time is not a problem since the system is stoped.
2-do you want to measure(or detect) the difference of the current and a 70.000mA reference?
I want to detect a small uA variation, and I'm thinking about using a current reference
3-What is the Max acceptable drop on the shunt resistor?
not important

thank you

 

[erikl]

For the full range you'd need a 17bit resolution, e.g. a **broken link removed** .

 

[Mehrshad74]

A 17bit ADC wont give true 17bit result because of linearity an offset errors.
for application like this a +20bit ADC with internal amplifier and differential input is a must.
Search analog device and you will find something that suits your application.

 

[Nik_Henri]

thanks alot for the tips it's well appreciate