ATtiny45 datasheet(119/196 Pages) ATMEL

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119

7598H–AVR–07/09

ATtiny25/45/85

Figure 18-8. Analog Input Circuitry

18.6.2

Analog Noise Canceling Techniques

Digital circuitry inside and outside the device generates EMI which might affect the accuracy of

analog measurements. If conversion accuracy is critical, the noise level can be reduced by

applying the following techniques:

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.

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

If any port pins are used as digital outputs, it is essential that these do not switch

while a conversion is in progress.

18.6.3

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 18-9. Offset Error

ADCn

IIH

1..100 kohm

CS/H= 14 pF

VCC/2

IIL

Output Code

VREF Input Voltage

Ideal ADC

Actual ADC

Offset

Error

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