The industry uses two common methods, called end point and best fit line method. Engineers from Freescale compare the two and found that the best fit line method gives more accurate results.
Many measurement applications require converting a slowly varying analog signal into digital with high accuracy and linearity. These often occur in industrial control, environmental monitoring, battery testing, and power consumption. All ADCs introduce static errors to measurements. Static parameters include offset error, full-scale error, gain error, and total unadjusted error. Nonlinear errors include integral non-linearity error and differential non-linearity error. In this article, we'll focus on offset and gain errors and compare two measurement methodologies.
Offset error is the difference between the actual first transition voltage and the ideal first transition voltage. Ideally, first transition takes place at a voltage equal to ½ LSB (least-significant bit).
Figure 1 shows the ideal and the actual transfer functions of an ADC. Here, offset error is measured at the first code transition.
Offset error causes the first code transition to occur at a higher input voltage than expected.
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