Datasheet

227
8284D–AVR–6/11
ATmega169A/PA/329A/PA/3290A/PA/649A/P/6490A/P
Figure 23-8. Analog Input Circuitry
23.7.2 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. The AVCC pin on the device should be connected to the digital V
CC
supply voltage via an
LC network as shown in Figure 23-9 on page 227.
3. Use the ADC noise canceler function to reduce induced noise from the CPU.
4. If any ADC port pins are used as digital outputs, it is essential that these do not switch
while a conversion is in progress.
Figure 23-9. ADC Power Connections
ADCn
I
IH
1..100 kΩ
C
S/H
= 14 pF
V
CC
/2
I
IL
VCC
GND
100nF
Analog Ground Plane
(ADC0) PF0
(ADC7) PF7
(ADC1) PF1
(ADC2) PF2
(ADC3) PF3
(ADC4) PF4
(ADC5) PF5
(ADC6) PF6
AREF
GND
AVCC
52
53
54
55
56
57
58
59
60
6161
6262
6363
6464
1
51
LCDCAP
PA0
10μΗ