Bypassing AVCC for analog comparison?

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#1
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I know that Atmel recommends filtering AVCC with an inductor and capacitor when you want to get good ADC. But is this important when using the analog comparator? I'd have thought that at least some of the noise would be common mode and might tend to be rejected by the comparator.

So, do I need to filter the AVCC if I am NOT doing any ADC, but I am using the comparator. FWIW, I am using the M328 for this project.

-Tony

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Probably not.

However, if there is a lot going on in your circuit, with many digital signals, I would add the filter.

For 10-bits accuracy (or 9) for normal ADC, it is recommened to use 10uH and 100nF for the AVcc. The AVcc is also the supply voltage for most pins of PORTA.
If some pins of PORTA are digital outputs, it is even recommended not to change them during an ADC conversion.

However I tested it with a small circuit with an analog temperature sensor. The accuracy was already good without a filter. But my circuit was very simple and I had Vcc decoupled with 100nF of course.

With the analog comparator mode there is rejection of noise. But I don't think that digital noise would be friendly enough to influence both inputs exactly the same.

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Good points. It would be simple enough to add the inductor. Already use the cap.