Datasheet

302
7766F–AVR–11/10
ATmega16/32U4
Figure 24-9. Analog Input Circuitry
24.7.2 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:
a. 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 digi-
tal tracks.
b. The AV
CC
pin on the device should be connected to the digital V
CC
supply voltage
via an LC network as shown in Figure 24-10.
c. Use the ADC noise canceler function to reduce induced noise from the CPU.
d. 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 24-10. ADC Power Connections
Note: The same circuitry should be used for AVCC filtering on the ADC8-ADC13 side
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
(ADC4) PF4
(ADC5) PF5
(ADC6) PF6
AREF
GND
AVCC
34
35
36
37
38
39
40
41
42
43
44
1
10µH