42
Subject to change without notice
V
in
0001
0010
0011
0100
0101
0110
Ue
Ideal function of
the a/d converter
Function of the a/d converter
is displaced by offset error
Z
(V
in
)
V
in
0001
0010
0011
0100
0101
0110
Ideal function of
the a/d converter
The slope of the function of the
a/d converter is affected by
amplification error
Z
(V
in
)
Fig. 2: A/D converter amplification error
Fig. 1: A/D converter offset error
V
in
0001
0010
0011
0100
0101
Z
(V
in
)
Bild 32: A/D-Wandler differentielle Nichtlinearit‰t
0110
V
in
Bild 32: A/D-Wandler differentielle Nichtlinearit‰t
Ideal function of
the a/d converter
(linear)
Actual from
interval V
in
at 0110
Ideal from interval V
in
at 0110
Nonlinearity of the
a/d converter
Fig. 3: A/D converter differential nonlinearity
0001
0010
0011
0100
0101
0110
Max. deviation of the nonlinear
slope curve of the a/d converter
to the ideal linear function
V
in
Z
(V
in
)
V
in
Ideal function of
the a/d converter
(linear)
Nonlinearity of the
a/d converter
Fig. 4: A/D converter integral nonlinearity
offset errors of the A/D converter
The input amplifier of the DMM is not properly adjusted and
shows an offset. This offset causes an offset error in the a/d
conversion. (Fig. 1)
Slope error (amplification factor error) of the A/D converter
The input amplifier’s amplification factor is temperature-
dependent, or the amplification factor was maladjusted. Hence
the slope of the function differs from the ideal value. (Fig. 2).
Differential nonlinearity of the A/D converter
The quantizing steps of the a/d converter are unequal in size
and differ from the ideal theoretical value. The differential
nonlinearity indicates how much each voltage interval (actual)
differs from the ideal voltage interval (ideal, 1 LSB)) ΔV
in
(Fig.
3) when the analog voltage Vin is being converted.
Differential linearity error = k x
Δ
V
in
;
k= factor, describing the relationship
Δ
V
in
(actual) to
Δ
V
in
(ideal)
linearity error (integral nonlinearity) of the A/D converter
Due to the individual differential linearity errors and their sum
a maximum error between the ideal conversion characteristic
and the actual one will accrue. The linearity error specifies the
maximum distance between the two functions (Fig. 4).
A/D conversion methods
In the following, the Single Slope, the Dual Slope and the Multip-
le Slope methods will be described. These sawtooth converters
are based on the same principle: conversion of the input voltage
into a proportional time span.
m e a s u r e m e n t P r i n c i p l e s a n d B a s i c s
