AN2438 Freescale Semiconductor / Motorola, AN2438 Datasheet - Page 7

• Manufacturer Part Number: AN2438
• Description: ADC Definitions and Specifications
• Manufacturer: Freescale Semiconductor / Motorola

Differential Non-Linearity (DNL)
MOTOROLA
$7
$6
$5
$4
$3
$2
$1
$0
Conversion
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Figure 3. Differential Non-Linearity, Missing Codes, and Non-Monotonicity Graphs
Differential Non-Linearity
REFL
DNL = 0.0
Input Voltage in LSB
1
DNL = +0.25
2
3
DNL = -0.25
4
5
Differential Non-Linearity (DNL) is the maximum of the differences in the each
conversion’s Current Code Width (CCW) and the Ideal Code Width (ICW). DNL
is the most critical of the measures of an ADC’s performance for many control
applications since it represents the ADC’s ability to relate a small change in
input voltage to the correct change in code conversion. DNL is defined as:
Some literature defines DNL using the Adjusted Code Width (ACW), which
means Zero- and Full-Scale Error have been adjusted for. For relatively
accurate ADC’s, the difference with respect to DNL is negligible, but using the
ACW complicates defining and testing DNL. Additionally, this definition is only
valid if the application has trim capability.
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Freescale Semiconductor, Inc.
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REFH
Code DNL = CCW – ICW
DNL = Max (Code DNL)
ADC Definitions and Specifications
$7
$6
$5
$4
$3
$2
$1
$0
Conversion
V
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REFL
DNL = -1.0
Input Voltage in LSB
1
Missing Code
2
3
4
Code $3 is
missing
5
6
7
V
REFH
$7
$6
$5
$4
$3
$2
$1
$0
Conversion
V
REFL
DNL = +1.5
Non-Monotonicity
Input Voltage in LSB
1
Differential Non-Linearity (DNL)
2
3
converted after $3
4
Code $2 is
5
6
7
V
AN2438/D
REFH
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