INA821: nA measurement using shunt resistor

jose del angel

Prodigy 10 points

Part Number: INA821
Other Parts Discussed in Thread: INA818, INA592

1) We want to measure nA with shunt resistance that can be 100 ohms, 1K or 100K.

2) Current range: 0~1000nA, step 10nA and Accuracy about of 1nA if possible but not required.

3) High side is required, Maximum voltage source system is ±5V(In step of ±10mV) .

4) The load is a semiconductor to measure the current consumption (about of 10nA by step).

5) supplies available are ±5V and ± analog output voltage range to ADC.

Do you have suitable analog solution in front end? Is possible to considerate INA818, INA821 or INA592.

In the future we could change the voltage source system to ±15V and maximize the sensing current range to 100mA using an external gain resistor (RG) or switching the shunt resistor.

over 2 years ago

0 Raymond Zhang1 over 2 years ago

TI__Guru 54981 points

Hi Jose,

In the simulation below, the current generator is scanned from -1uA to 1uA linearly. With Gain = 1001 V/V and Rsense = 1kΩ, linear output response is generated. So the configuration should work for sensing in low and high side.

There is an approx. 10mV associated with the offset voltage at the output of the INA821, but the 10mV offset, Vos is a fixed voltage and it may be calibrated out.

Enclosed is the simulation in Tina.

INA821 nA Isense 04192022.TSC

With dual supply voltage rails, ±5Vdc or ±15Vdc, there should not have significant common mode constraint in the configuration, see the plot below.

You may down the tool for analysis from the link below.

https://www.ti.com/tool/ANALOG-ENGINEER-CALC

Per nA-uA low current sensing application with large sensing resistor (>1kΩ) and/or large gains, INA818 should work as well. INA592 is a difference amplifier and its gains (0.5V/V or 2V/V) are fixed, and it may not be applicable for the application.

With measuring in low current, have you considered to use transient impedance amplifier or I-to-V converter for the measuring application? What is the current sensing application?

Best,

Raymond