77
ATmega103(L)
0945G–09/01
ADC Noise Canceling
Techniques
Digital circuitry inside and outside the ATmega103(L) 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 ATmega103(L) and all analog components in the applica-
tion 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 ATmega103(L) should have its own decoupling capacitor as
shown in Figure 49.
4.
Use the ADC Noise Canceler function to reduce induced noise from the CPU.
5.
If some Port F pins are used as digital inputs, it is essential that these do not
switch while a conversion is in progress.
Figure 49.
ADC Power Connections
VCC
GND
10nF
Analog Ground Plane
ATmega103(L)
(ADC0) PF0
(ADC7) PF7
(ADC1) PF1
(ADC2) PF2
(ADC3) PF3
(ADC4) PF4
(ADC5) PF5
(ADC6) PF6
AREF
AGND
AVCC
52
53
54
55
56
57
58
59
60
61
61
62
62
63
63
64
64
1
51
PEN
(AD0) PA0