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8048B–AVR–03/09

• Keep analog tracks well away from high-speed switching digital tracks.

• Use the ADC noise canceler function to reduce induced noise from the CPU.

• If any port pin is used as a digital output, it mustn’t switch while a conversion is in progress.

• Place bypass capacitors as close to V

CC and GND pins as possible.

Where high ADC accuracy is required it is recommended to use ADC Noise Reduction Mode, as

described in Section 16.7 on page 121. This is especially the case when system clock frequency

is above 1 MHz, or when the ADC is used for reading the internal temperature sensor. A good

system design with properly placed, external bypass capacitors does reduce the need for using

ADC Noise Reduction Mode

16.10 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 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 16-9. Offset Error

Output Code

VREF Input Voltage

Ideal ADC

Actual ADC

Offset

Error

ATtiny43U 데이터시트(PDF) 123 Page - ATMEL Corporation