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RE: [avr-gcc-list] ATmega16 ADC at High Clock Rates

From: Kristian Saether
Subject: RE: [avr-gcc-list] ATmega16 ADC at High Clock Rates
Date: Wed, 17 Aug 2005 16:01:34 +0200

Tom, Dave

When the ADC clock frequency is above 1Mhz the accuracy of the ADC will degrade 
quickly. We do not recommend using it with a faster clock than 1Mhz so we do 
not test or
characterise the ADC at higher speeds than 1Mhz.

The actual resolution at 2Mhz will probably be 5-6 bits. That should be 
something in the
range of 30 LSB...
I think there are people using the ADC with a 2-4Mhz frequency in applications 
where they
only need 2-4 bits resolution, but I have not seen it in real life. If you can 
live with a
lower resolution than 8 bit you could alsways test the ADC at 2Mhz and see if 
the result
is something you can use in your application.

Best Regards,
Kristian Saether
AVR Applications Engineer 

> From: User Tomdean <address@hidden>
> [...]
> >
> >The ATmega16 datasheet states, in part,
> [...]
> >   resoultion.  If a lower resolution than 10 bits is needed, the input
> >   clock frequency to the ADC can be higher than 200 kHz to get a
> >   higher sample rate.
> >
> >The datasheet does not specify the reduction in resolution due to a
> >higher clock rate.
> >
> >Before I measure, does anyone know the reduction in resoultion, say,
> >at 1 mHz?  2 mHz?
> Table 122 on page 295 of my ATmega16 datasheet gives a typical absolute 
> accuracy of 3 LSb, maximum of 4, at 1 MHz.  It also give 1MHz as the maximum 
> ADC clock frequency.  No numbers are given for 2 MHz.
> Regards,
>    -=Dave
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