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The datasheet for the ATtiny861a states that "If the ADC is used AVCC should be connected to VCC through a low-pass filter". The datasheet doesn't specify what values I should use or what style of low-pass filter I should use. The ATMega datasheets on the otherhand state that the low-pass filter should be a 10uH inductor connecting AVcc to Vcc with a 100nF capacitor connected to ground. Is this the same style of low-pass filter I should be using for my ATtiny or is there something better?

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  • \$\begingroup\$ What frequencies will the parts of your system be running at? \$\endgroup\$ Jun 8 '15 at 16:27
  • \$\begingroup\$ The clock speed will be ~8Mhz \$\endgroup\$ Jun 8 '15 at 16:33
  • \$\begingroup\$ The only ADC inputs are from a KXTC9-4100 accelerometer kionix.com/sites/default/files/… \$\endgroup\$ Jun 8 '15 at 16:34
  • \$\begingroup\$ the 10uH and 100nF LC filter is about 160Khz cut-off frequency. Seems reasonable to reduce clock and RF noise. Use a little ferrite bead and a little SMD cap, should be easy! \$\endgroup\$
    – KyranF
    Jun 8 '15 at 20:41
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I think the ATmega advice is pretty good. With L1 = 10uH and C1 = 100nF, the 8MHz processor frequency is down over 60dB. I added a series resistor R2 = 10Ω to reduce the resonant peak of the LC pair. It may be not necessary, though.

Circuit

schematic

simulate this circuit – Schematic created using CircuitLab

Frequency response

Frequency response

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