ATmega8(L)
Analog Noise
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of
Canceling Techniques 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
ground plane, and keep them well away from high-speed switching digital tracks.
2. The AVCC pin on the device should be connected to the digital VCC supply voltage via
an LC network as shown in Figure 96.
3. Use the ADC noise canceler function to reduce induced noise from the CPU.
4. If any ADC [3..0] port pins are used as digital outputs, it is essential that these do not
switch while a conversion is in progress. However, using the Two-wire Interface
(ADC4 and ADC5) will only affect the conversion on ADC4 and ADC5 and not the
other ADC channels.
Figure 96. ADC Power Connections
PC1 (ADC1)
PC0 (ADC0)
ADC7
GND
AREF
ADC6
AVCC
PB5
ADC Accuracy
Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and VREF in 2n 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
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2486AA–AVR–02/2013
ATMEL [ ATMEL ]
