Rainbow Electronics ATmega32L - Manual (Page 208)

208
ATmega32(L)
2503C–AVR–10/02
Figure 105. Analog Input Circuitry
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 106.
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 106. ADC Power Connections
ADCn
I
IH
1..100 k
Ω
C
S/H
= 14 pF
V
CC
/2
I
IL
GND VCC P
A0 (ADC0)
P
A1 (ADC1)
P
A2 (ADC2)
P
A3 (ADC3)
PA4 (ADC4)
PA5 (ADC5)
PA6 (ADC6)
PA7 (ADC7)
AREF
AVCC
GND
PC7
10
µ
H
100nF
Analog Ground Plane