ATtiny5 datasheet(90/168 Pages) ATMEL

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8127C–AVR–10/09

ATtiny4/5/9/10

13.9 Noise Canceling Techniques

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

analog measurements. When 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.

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

• 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 VCC and GND pins as possible.

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

described in Section 13.7 on page 88. A good system design with properly placed, external

bypass capacitors does reduce the need for using ADC Noise Reduction Mode

13.10 ADC Accuracy Definitions

An n-bit single-ended ADC converts a voltage linearly between GND and VREF 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 (0x00 to 0x01) compared to the ideal transition (at

0.5 LSB). Ideal value: 0 LSB.

Figure 13-9. Offset Error

Output Code

VREF Input Voltage

Ideal ADC

Actual ADC

Offset

Error

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