XTR300: Definitions of Specifications of Gain Nonlinearity in voltage output mode and Linearity Error in current output mode

Hi Shinichi,

Please refer to my answers below.

Q1.) Gain Nonlinearity" in voltage output mode, does this parameter correspond to the DNL of the A/D converter, or does it refer to the INL?

DNL refers to the ADC step size and how it differs from the ideal 1LSB value while INL refers to the non-linearity of the ADC transfer function across all of the codes. These characteristics are with respect to the analog voltage at the input of the ADC, and are dependent on the ADC chosen in your application. 

Errors and non-linearities that occur in the signal chain before the ADC do not effect the DNL or INL spec, as these specifications are always referred to the voltage present at the input of the ADC. Gain nonlinearity is similar in principle to INL, as these both represent the deviation from a straight line (ideal transfer function), see Q2 below.

Q2.) The unit of "Gain Nonlinearity" is "%FS"...

Note that gain linearity is not the same as gain error. Below I simulated two ideal amplifiers in a gain of 2 V/V, but one with a 5% gain error caused by the tolerance of feedback resistor R3. Note that although the gain error is 0% for the green curve and 5% for the red curve, both of these curves are perfectly linear.

Gain nonlinearity is specified as the max deviation in percent of span of output value from the straight line, as shown in the figure below.

The gain error is determined by comparing the worst case gain compared to the ideal gain. For the XTR300 in voltage output mode, gain error is specified as %FS where the input is 0V-4V and the output is ±10V. To determine the worst case gain error we would use the max specification for gain error, not the maximum specification for gain nonlinearity, although in this case they are both specified as ±0.1% full scale, and your calculations produced the correct value.

Q3.)  Unfortunately, we do not have a graph of nonlinearity vs output voltage.

Q4.) See Q1 above.

Q5.)  "linearity error in current output mode" is also in "%FS"...

The same principles discussed in Q2 about linearity error vs gain error apply for the current output mode. The specified max gain error is ±0.12 %FS. Therefore for a FS output of ±20mA the max gain error is ±48 μA. The specified max linearity error is ±0.1 %FS. Therefore for a current output of ±20mA, so the max linearity error is ±40 μA.

Thanks,

Zach