AVR-Chat

At 10:50 AM 8/2/2004, Larry Barello wrote:

>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. 

Sure. Goes without saying that if you draw enough through the resistor to get any significant droop, it will be a problem, at least for ratiometric conversions.

> 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.

If the system's not too noisy.