atmega32c1 ATMEL Corporation, atmega32c1 Datasheet - Page 236

• Manufacturer Part Number: atmega32c1
• Description: Atmega32m1 Automotive 8-bit Avr Microcontroller With 32k/64k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

18.6.3
18.6.4
236
ATmega32/64/M1/C1
Offset Compensation Schemes
ADC Accuracy Definitions
The gain stage has a built-in offset cancellation circuitry that nulls the offset of differential mea-
surements as much as possible. The remaining offset in the analog path can be measured
directly by shortening both differential inputs using the AMPxIS bit with both inputs unconnected.
(See “Amplifier 0 Control and Status register – AMP0CSR” on page
trol and Status register – AMP1CSR” on page
register – AMP1CSR” on page
the measurement results. Using this kind of software based offset correction, offset on any chan-
nel can be reduced below one LSB.
An n-bit single-ended ADC converts a voltage linearly between GND and V
(LSBs). The lowest code is read as 0, and the highest code is read as 2
Several parameters describe the deviation from the ideal behavior:
•
Figure 18-10. Offset Error
•
Offset: The deviation of the first transition (0x000 to 0x001) compared to the ideal transition
(at 0.5 LSB). Ideal value: 0 LSB.
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
Output Code
Offset
Error
252.). This offset residue can be then subtracted in software from
252.and
See “Amplifier 1 Control and Status
V
REF
251.,
Input Voltage
n
-1.
See “Amplifier 1 Con-
Ideal ADC
Actual ADC
REF
7647A–AVR–02/08
in 2
n
steps