Rainbow Electronics ATmega64C1 - Manual (Page 235)

235
7647A–AVR–02/08
ATmega32/64/M1/C1
Figure 18-8. Analog Input Circuitry
18.6.2 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 AV
CC
pin on the device should be connected to the digital V
CC
supply voltage via
an LC network as shown in Figure 18-9 .
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 18-9. ADC Power Connections
ADCn
I
IH
1..100 k Ω
C
S/H
= 14 pF
V
CC
/2
I
IL
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
VCC
GND
(ACMPN3/ADC0) PE2
(ADC1) PD4
PB7(ADC4)
PB6 (ADC7)
PB5 (ADC6/ACMPN1/AMP2-)
PC7 (D2A/AMP2+)
PB4 (AMP0+)
PB3 (AMP0-)
PC6 (ADC10/ACMP1)
AREF (ISRC)
AGND
AVCC
PC5 (ADC9/ACMP3/AMP1+)
PC4 (ADC8/AMP1-)
PB2 (ADC5/ACMPN0)
PD7 (ACMP0)
PD6 (ADC3/ACMPN2)
PD5 (ADC2/ACMP2)
100nF
Analog Ground Plane
10
μ
H