AVR-Chat

Remember that Avcc supplies power to the analog port I/O pins (i.e. if you
use them for regular I/O).  Even if you only use them for analog inputs, the
Schmitt trigger is still active - drawing different current levels for '0'
vs '1'.  If you use Avcc as your reference and if you have too much
resistance on the Avcc line, you will get artifacts on your ADC readings.  I
found out the hard way once with a 100 ohm resistor/cap on the Avcc line...
That is why an inductor is usually recommended.  I find that a simple analog
ground plane connected to everything else at one point with a seperate
bypass cap at Aref & Avcc is good enough.

Of course the problem is much worse if you use some of those lines as
outputs...

-----Original Message-----
From: David VanHorn

>
>What method do you recomend for sourcing +V and -V to the opamp?

Analog and digital grounds ideally are separated, and meet under the micro.
I use 0 ohm resistors, since it's an easy way to fool your cad package into
considering AGND and DGND as separate things.

I take VCC through a small resistor (1-10 ohms) to AVCC, with a large-ish
cap to AGND.
Inductors are more effective, but also more expensive.  I've not yet needed
to resort to the inductor solution.