Precision 1nA - 10mA current source

Question

I need design a variable precision current source which able to produce 1nA to 10mA. The current output will be controlled through a Micro controller using a DAC. The purpose this circuit is to calibrate another device which need 1nA to 10mA.

I did some research and found below options:

1. Analog Devices: Precision Nanoamp Bidirectional Current Source Not enough information to how can be modified for my application

2. simple opamp and Mosfet which output current should be I = Vdac/(R4 or R3) Figure

3. Also I read about Multi-Range Current Pump too.

^{simulate this circuit – Schematic created using CircuitLab}

(*forget about the part numbers on drawing, just for reference)

Please let me know if any of these option will work for me, or if there is better option out there.

How can I design a precision 1nA - 10mA current source circuit?

Answer 1

These circuits work well, I've built several variations of them to deliver accurate amounts of current, but mostly on the load side. I have a few suggestions:

• Use a low noise amplifier
• Use a low leakage mosfet

• Make sure the feedback loop is compensated properly, the mosfet has small amounts of capacitance and can create poles in the kHz to MHz range. If the poles are higher than the DC gain, then this can create a resonance point and causes oscillations. The best way is to simulate in SPICE with different DC levels while running an AC analysis to ensure stability.

• Make sure you use a low noise DAC

• If you use a MUX put the feedback loop so it includes the mux (this is a big hint).

• Instead of a mux, if the leakage could be controlled, you might be able to use two circuits in parallel.

The circuit above simulates down to 1nA with a 1mV input.

If you need absolute calibration to a specific level of current, I'd buy a Keithly current source meter (like the 2400 Keithly SMU)