AMC1302-Q1: What do "TCEG Nonlinearity" and "TCEG Nonlinearity drift" mean?

Hi Ochi-san,

The transfer function for an ADC can be shown in terms of y=mx+b, where the x axis is the input voltage and the y axis is the corresponding output voltage. There are three main terms that describe the accuracy of this transfer function. Offset, gain, and nonlinearity. Each of these terms also have a corresponding drift specification to define how these terms change in response to changes in temperature.

• Offset is the "b" term from the y=mx+b equation.
• Gain is the "m" term from the y=mx+b equation.
• Nonlinearity accounts for the errors not represented by the y=mx+b equation. Often caused by the complex inner-workings of the device.

 Below shows an example transfer function.

• Red shows the real raw output transfer function without any calibration, while green shows the ideal transfer function, what the output would be if the ADC was perfect.
• Purple shows the output transfer function after performing an offset calibration: This can be accomplished by shorting the inputs of the ADC together, recording the output result, then subtracting that result from the subsequent raw outputs.
• Blue shows the output transfer function after performing a gain and offset calibration. This is accomplished by applying a very precise signal source to the input of the signal chain at two different magnitudes, such as +10% and – 10% or 20% and 80% of the full-scale input range, recording the output values and calculating the transfer function (shown by the dotted blue line). This transfer function can then be compared to the ideal transfer function (shown as the green line) and adjusting the subsequent raw outputs accordingly.
• The variation between the green "ideal ADC" line and the blue "ADC after offset and gain correction" is the nonlinearity.

From the AMC1302-Q1 datasheet:

TCEG stands for "temperature coefficient Error Gain" Also known as gain error drift. TCEG does not apply to nonlinearity and nonlinearity drift. 

Please let me know if you have additional questions.