ATTINY25_07 Datasheet, PDF (125/201 Pages) ATMEL Corporation – 8-bit Microcontroller with 2/4/8K Bytes In-System Programmable Flash

ATtiny25/45/85 Auto
19.6.3
a. Keep analog signal paths as short as possible. Make sure analog tracks run over
the analog ground plane, and keep them well away from high-speed switching digi-
tal tracks.
b. Use the ADC noise canceler function to reduce induced noise from the CPU.
c. If any port pins are used as digital outputs, it is essential that these do not switch
while a conversion is in progress.
ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and V_REF in 2ⁿ steps
(LSBs). The lowest code is read as 0, and the highest code is read as 2ⁿ-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 0.5 LSB). Ideal value: 0 LSB.
Figure 19-9. Offset Error
Output Code
Ideal ADC
Actual ADC
Offset
Error
V_REF Input Voltage
• 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 1.5 LSB below maximum).
Ideal value: 0 LSB
Figure 19-10. Gain Error
Output Code
Gain
Error
7598D–AVR–02/07
Ideal ADC
Actual ADC
V_REF Input Voltage
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