Datasheet

ATtiny13

2535E–AVR–10/04

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:

1. 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 digital tracks.

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

3. 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 2

steps (LSBs). The lowest code is read as 0, and the highest code is read as 2

-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 48. Offset Error

• 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

REF

Input Voltage

Ideal ADC

Actual ADC

Offset

Error