Hi,

Can anyone tell me precise method for error budgeting for DC measurement? temperature,INL,DNL,Offset,drift, TUE ... How to bring everything on one calculator?

Is anyone having some tool or excel to find out the total DC measurement error over complete temperature range ?

ADC I am using is AD7685.

Pls brainstorm on this important topic.

Regards,

Chaitanya

Chaitanya,

To implement a correction, you can't simply just add the effects of gain error to the offset error. The gain error correction should ideally be implemented as a multiplication if possible. The correction coefficient should be calculated as follows:

Correction Coeff = Max Device Code / (Measured Reference * Measured Device Slope)

Now with this correction coefficient, we could figure out the ideal code the device should be producing for a given input stimulus. Assuming we have our measured offset coefficient, we would first subtract that from our observed output code and then multiple this value by our slope correction. Here is a real world example: Let's say our device has a 10 lsb offset and a 10 lsb gain error when we are using a 5 volt reference. For a 16-bit device, our measured slope would be 65546 / 5 (this is 65536 + 10 lsb gain error divided by the reference). Therefore, the measured slope is 13109.2 device codes per volt. Our correction coeff is going to equal 65536/(5*13109.2) = 0.99985. Our correction equation will be: Corrected Output Code = (Observed Code - 10) * 0.99985.

I would not recommend RSS-ing the errors as they are completely independent values with different units. The aggregate accuracy of the measurement changes as you move through the transfer function since the gain error is a ratio.

The offset error will change with temperature environment. I think the average value will work just fine here because implementing a system for offset drift correction would be quite cumbersome.

I'm a bit confused, by this last question, but TUE is the maximum amount of error a user could expect if they made no corrections, hence, total unadjusted error. We aren't adjusting the actual TUE of the device, we are just accounting for it in our post processing.

--Ryan