AVCC?

The Atmega datasheets recommend a LC filter for the AVCC (analog power) pin. None of the Arduino schematics seem to implement this. Was there any research into just what those parts might buy in terms of noise reduction on the analog pins? Some of the Atmel boards out there seem to use the filter, and others, similar to Arduino, ignore the issue. I've also seen RC filters used. I dug through the datasheet a bit and didn't find an input impedance for the AVCC pin, anyone have info on that?

Anyone on the Arduino hardware side have any insight here?

Paul Badger

hi

You're right, it would probably help things to have separate AVCC filtering.

On the other hand, I'm guessing such things were left out for cost reasons. A cheap inductor and capacitor on AVCC could add 25 cents to the manufacturing costs, adding $2,500 to the cost of the 10K units already manufactured. Are there that many users who need that kind of noise rejection? The 10Uh inductor Atmel cites would probably help things, as would a nice ground plane and lots more bypassing... sort of the deluxe version!

D

If you're interested, the newest revision of the bare-bones board has that filter on-board.