ADC errors

AN2719

8/22

2

ADC errors

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

Linearity errors

2.2.1

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

Figure 8.

DNL: missing code

Ideal ADC

Real ADC

DNL = - 0.5 LSB

no missing code

ADC output

[code]

110

101

100

011

010

001

000

Input voltage

[V]

Ideal ADC

Real ADC

DNL = - 1.5 LSB

missing code 011

ADC output

[code]

110

101

100

011

010

001

000

Input voltage

[V]