AN2719 Datasheet, PDF (8/22 Pages) STMicroelectronics – Precision improvement techniques

ADC errors
2
ADC errors
AN2719
2.1
Introduction
This chapter lists the main errors which have an effect on A/D conversion accuracy. These
types of error occur in all A/D converters and conversion quality depends on eliminating
them. You can find values for these errors specified in the ADC characteristics section of any
STM8 datasheet. The datasheets also include sections describing sources of error or
methods for minimizing them.
2.2
2.2.1
Linearity errors
Differential nonlinearity
Differential nonlinearity (DNL) shows how far a code is from a neighboring code. The
distance is measured as a change in input voltage magnitude and then converted to LSBs.
The best ADC performance is specified as "no missing codes". This means that if the input
voltage is swept over its range, all output code combinations will appear at the converter
output. A DNL error of <±1LSB guarantees no missing codes. With a DNL equal to -1LSB,
the ADC does not guarantee to have no missing codes. With a DNL greater than -1, the
device has missing codes.
Figure 7.
DNL: no missing codes
ADC output
[code]
110
101
Real ADC
100
DNL = - 0.5 LSB
011
no missing code
010
Ideal ADC
001
000
Input voltage
[V]
Figure 8.
DNL: missing code
ADC output
[code]
110
101
Real ADC
100
DNL = - 1.5 LSB
011
missing code 011
010
Ideal ADC
001
000
Input voltage
[V]
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