Rainbow-electronics ATmega64M1 Manual do Utilizador descarregar pdf (Página 233)

233

8209A–AVR–08/09

ATmega16M1/32M1/64M1

to remove high frequency components with a low-pass filter before applying the signals as

inputs to the ADC.

Figure 22-8. Analog Input Circuitry

22.6.2 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 22-9.

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 22-9. 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 ... 228 229 230 231 232 233 234 235 236 237 238 ... 342 343

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