Dear Alan, i am a bit confused regarding circuits. I dont know which one is a main circuit to measure pico ampere current, secondly , what about calibration ,i mean what can be said about accuracy of reading obtained through this circuit.Can you describe a bit more about the drawings in the second picture, i mean which will work as pico ammeter and why you draw rest of other circuits.

thanks

As another option to measure nanoamperes level currents I am using the regular manual range digital multimeters. On DC 200 mV range depending the input impedance, I can measure fsd 200.0 nanoamperes with 1 Megaohm input impedance or fsd 20.00 nanoamperes with 10 Megaohm input impedance meter. To find the leakage current of Si diodes before using them on some sensitive circuits or checking car alternators' excitation bridges for leakage this is pretty useful.

Alan,

Thank you for your answers my question very much! I'm clear now.

Whould you like accept my greetings it come from China where at far away the east?

Thanks again!

Regards.

yi gang.

Yi,

The "rail-splitter" amp is acting as a unity-gain follower, delivering a mid-rail voltage to the shielding box. I could just have easily used two batteries, but there were two op-amps in the package and it consumes only tiny currents keeping the "ground" at mid-rail.

You can actually buy rail-splitter devices which are implemented internally essentially identical to this. They have complementary outputs that sink or source current to keep the output at half the supply voltage. (Up to some limit where they blow up. :)

Regards,

Alan

Why it does'nt got a large current consume that OPA. generate the referenced ground?