Atmel AT90PWM2 Manual page 241

21.6.2 Analog Noise Canceling Techniques
AT90PWM2/3/2B/3B
242
Figure 21-8. Analog Input Circuitry
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 AV pin on the device should be connected to the digital V
CC
an LC network as shown in
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 21-9. ADC Power Connections
(ADC0) PE2
(ADC1) PD4
I
IH
ADCn
I
IL
Figure 21-9.
32
1
31
2
30
3
29
4
28
5
27
6
26
7
VCC 25
8
GND 24
9
23
10
22
11
21
12
20
13
19
14
18
15
17
16
1..100 kΩ
C = 14 pF
S/H
V
CC
supply voltage via
CC
PB7(ADC4)
PB6 (ADC7)
PB5 (ADC6)
PC7 (D2A)
PB4 (AMP0+)
PB3 (AMP0-)
PC6 (ADC10/ACMP1)
AREF
AGND
AVCC
PC5 (ADC9/AMP1+)
PC4 (ADC8/AMP1-)
PB2 (ADC5)
PD7 (ACMP0)
PD6 (ADC3/ACMPM)
PD5 (ADC2/ACMP2)
Analog Ground Plane
/2
100nF
4317I–AVR–01/08