Datasheet

132
ATmega323(L)
1457E11/01
ADC Noise Canceling
Techniques
Digital circuitry inside and outside the ATmega323 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. The analog part of the ATmega323 and all analog components in the application
should have a separate analog ground plane on the PCB. This ground plane is
connected to the digital ground plane via a single point on the PCB.
2. 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.
3. The AV
CC
pin on the ATmega323 should be connected to the digital V
CC
supply
voltage via an LC network as shown in Figure 65.
4. Use the ADC noise canceler function to reduce induced noise from the CPU.
5. If some Port A pins are used as digital outputs, it is essential that these do not
switch while a conversion is in progress.
Figure 65. ADC Power Connections
GND
VCC
PA0 (ADC0)
PA1 (ADC1)
PA2 (ADC2)
PA3 (ADC3)
PA4 (ADC4)
PA5 (ADC5)
PA6 (ADC6)
PA7 (ADC7)
AREF
AVCC
AGND
PC7
10µΗ
100nF
Analog Ground Plane
ATmega32
33
29
31
27
26
32
28
30
37 3536 3438
39