ADC Errors
• Ideal ADC
– Input is quantized into uniform
steps.
6
4
D igital Output
– Transitions at +/- 50% of ∆
Ideal ADC
8
2
0
-2
-4
-6
-8
-8
-6
-4
-2
0
Analog Input
2
4
6
8
ADC Errors
• Offset Error
– Expressed as number of LSBs
(counts)
– Total system offset error
includes offset error from
preamplifiers or signal
transducers.
6
4
D igital Output
– Defined as a constant
difference, over the whole
range of the ADC, between the
actual output value and the
ideal output value.
Offset Error
8
2
0
-2
-4
-6
-8
-8
-6
-4
-2
0
2
Analog Input
Offset error can be removed be measuring a reference point and
subtracting that value from future samples.
4
6
8
ADC Errors
• Gain Error
– Expressed as a percentage.
– Total system gain error includes
any gain errors from
preamplifiers, attenuators, or
signal transducers.
6
4
D igital Output
– Defines as the difference of the
slope of the actual output values
and the ideal output values.
Gain Error
8
2
0
-2
-4
-6
-8
-8
-6
-4
-2
0
2
4
Analog Input
Gain error can be removed be measuring a second reference point to
determine the actual gain.
6
8
ADC Errors
• Differential Non-Linearity
– Any deviation from the ideal step
width is the Differential NonLinearity. (DNL)
– Expressed as counts.
6
4
Digital Output
• For an ideal ADC the output is
• divided into 2n uniform steps
• each with the width ∆.
DNL Error
8
2
0
-2
-4
-6
-8
-8
-6
-4
-2
0
2
4
Analog Input
DNL is a function of each ADC’s particular architecture. It is not possible
to remove its effects with calibration.
6
8
ADC Errors
• Integral Non-Linearity
INL Error
• DNL errors accumulate to
produce a total Integral NonLinearity (INL).
– Measured from the center of the
step.
– Expressed as counts.
6
4
D igital Output
– Defined as the maximum
deviation from the ideal line.
8
2
0
INL
-2
-4
-6
-8
-8
-6
-4
-2
0
2
4
6
Analog Input
INL is a function of each ADC’s particular architecture. It is not possible to
remove its effects with calibration.
8