INA118: Minimum input voltage to the INA118 to be recognized

Hi Tawfiq,

Thank you for your post, I can help you. 

The input voltage range of an instrumentation amplifier depends on many parameters, including supply voltage, reference voltage, gain and common mode voltage. I would recommend downloading a calculator tool called the "Analog Engineer's Calculator": https://www.ti.com/tool/ANALOG-ENGINEER-CALC 

This tool has several different calculators including the INA boundary plot tool (Click on Amplifiers and Comparators >> INA VOUT vs VCM). From here, you can select the instrumentation amplifier you're using, enter in the supply voltage, reference voltage, gain and common mode voltage, and the tool will tell you the input differential voltage range and output voltage swing allowed for linear behavior. 

For instance, let's take the INA118 for example. Let us assume we are operating with +/-15V supplies, reference = 0V, common mode voltage = 0V, and the gain = 10V/V. The input voltage range that we can precisely process with the INA118 is -1.48V to 1.42V to yield a linear output voltage swing of -14.8V to 14.2V.

I hope this helps! 

To learn more about instrumentation amplifiers, please watch these training videos where I go over all these parameters and how a boundary plot can be useful for your circuit design: https://training.ti.com/ti-precision-labs-introduction-instrumentation-amplifiers?context=1139747-1139745-1140241-1140068 

Thank you for the fast reply.

Just want to make sure before I order the in-amp: I got in the calculator:

V+:  -3.6-2.067

V-:   -2.067-3.6

Vin:  4.133--7.2

Vout max = 8.2

Vout min=-8.2

So does that mean that any voltage for V+,V-, Vin between the given ranges would be read? 

even it's resolution is very small? for example Vin=2mV?

Thank you.

Hi Tawfiq,

I'm confused by your setup.

• What is V+ and V-? Are these your voltage supplies? Pin 4 and 7
• What is -3.6-2.067? 

The best way to do this would be to answer the following questions for me:

• What are your voltage supplies? Pin 4 and 7
• What is your expected gain? What resistor value do you have connected between pins 1 and 8?
• What is your differential voltage? This is the voltage you are trying to amplify.
• What is the common mode voltage? This is the voltage you are trying to reject.
• What is your reference voltage? This is a output level-shifter.
• What is your expected output?

I highly recommend following the training videos I sent you as well, as this will outline all these pins and explain what they are.

It would also be helpful if you put together a circuit in TINA Spice and simulated it. That way you can see how it's behaving. 

TINA simulator can be downloaded here: https://www.ti.com/tool/TINA-TI 

INA118 model can be downloaded here, download the .tsc file: https://www.ti.com/product/INA118#design-development 

Hi Tawfiq,

why not just showing your schematic? And tell something about your application :-)

Kai

voltage supplies are +3.3V and -3.3V

expected gain 1.1: Rg=500KOHm

differential voltage is 2 mV

common mode=0 (how do you change this anyway?)

reference voltage: 1V

My concern is: 

The non-inverting has an AC signal of 25mV (zero offset)

inverting is AC of 23mV

Will this in-amp read the inputs?

when the calculator is showing a min-max range, any voltage in between is fine with the amp?

Thank you!!

I'm trying to build an impedance analyzer