Rainbow-electronics ATmega64C1 Manuale Utente Scaricare il pdf (Pagina 235)

100

101

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

pin on the device should be connected to the digital V

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

1..100 kΩ

S/H

= 14 pF

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

10μH

1 2 ... 230 231 232 233 234 235 236 237 238 239 240 ... 365 366

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