1.2 Offset Error

Offset error is defined as the deviation of the transfer function's midpoint from the actual measurement compared to the ideal. Offset is calculated using histogram hits to determine the center point of the measured transfer function. The upper and lower 256 bins of the measured transfer function are excluded. The difference between the measured middle code and n/2 is the offset. The number of hits in the measured center bin provides resolution beyond 1 LSB. Offset error can be either positive or negative. Measuring negative offset requires a stimulus voltage below 0V. The offset error is corrected by adding or subtracting the offset error from the output. Figure 1-3 shows an example of a positive offset error.