Datasheet

239
2467X–AVR–06/11
ATmega128
ADC Accuracy
Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and V
REF
in 2
n
steps
(LSBs). The lowest code is read as 0, and the highest code is read as 2
n
-1.
Several parameters describe the deviation from the ideal behavior:
• Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition
(at 0.5LSB). Ideal value: 0LSB.
Figure 115. Offset Error
• Gain Error: After adjusting for offset, the gain error is found as the deviation of the last
transition (0x3FE to 0x3FF) compared to the ideal transition (at 1.5LSB below maximum).
Ideal value: 0LSB
Figure 116. Gain Error
• Integral Non-linearity (INL): After adjusting for offset and gain error, the INL is the maximum
deviation of an actual transition compared to an ideal transition for any code. Ideal value:
0LSB.
Output Code
V
REF
Input Voltage
Ideal ADC
Actual ADC
Offset
Error
Output Code
V
REF
Input Voltage
Ideal ADC
Actual ADC
Gain
Error