AVR-Chat

I don't see that a mega8 has the diff (gain) mode

On Thu, 1 Dec 2005 18:52:46 +0200
"MuRaT KaRaDeNiZ" <karademu.yahoogroups@onlinefavbar.com> wrote:

> But be aware that the analog bandwith falls when internal gain is
> enabled:
> 
> >From AVR120 (doc2559.pdf):
> 
> "When using single-ended mode, the ADC bandwidth is limited by the ADC
> clock
> speed. Since one conversion takes 13 ADC clock cycles, a maximum ADC
> clock of 1
> MHz means approximately 77k samples per second. This limits the
> bandwidth in
> single-ended mode to 38.5 kHz, according to the Nyquist sampling
> theorem.
> 
> 
> When using differential mode, the bandwidth is limited to 4 kHz by the
> differential
> amplifier. Input frequency components above 4 kHz should be removed by
> an
> external analog filter, to avoid non-linearity's."
> 
> 
> And one question, atmega8 has not gain block, do i miss something?
> 
> 
> Regards
> 
> Murat Karadeniz
> http://www.onlinefavbar.com/mukas
> 
> 
> -----Original Message-----
> From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
> Behalf Of Mehdi Ghassemi
> Sent: Wednesday, November 30, 2005 10:39 PM
> To: AVR-Chat@yahoogroups.com
> Subject: RE: [AVR-Chat] Question on using AVR (Mega8) ADC for low
> voltage measurements
> 
> 
> Hi jim
> the atmel company has guarantied vref=2.3v for ref pin,ofcourse i use
> 1.25v and I dont have problem,but you can use 200x internal gain in
> atmega8 and Vref=Avcc,therefor you can't 0.1V for Vref because the ADC
> can't work, 
> 
> --- MuRaT KaRaDeNiZ <karademu.yahoogroups@onlinefavbar.com> wrote:
> 
> > Hello James,
> > 
> > Some suggestions:
> > Choose a voltage reference implementation with minimal noise, since 
> > now 100uV noise becomes 1bit of the result, and simple voltage 
> > references/regulators surely have more noise than that. Make use of RC
> 
> > filtering on reference voltage. if you use simple resistor divider, do
> 
> > not take too high resistor values, since thermal noise in a resistor 
> > is proportional to square root of resistance value.
> > 
> > Don't forget to inform us about the results.. :)
> > 
> > Regards
> > 
> > Murat Karadeniz
> > http://www.onlinefavbar.com/mukas
> > 
> > 
> > -----Original Message-----
> > From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On 
> > Behalf Of James Washer
> > Sent: Sunday, November 27, 2005 10:16 PM
> > To: AVR-Chat@yahoogroups.com
> > Subject: [AVR-Chat] Question on using AVR (Mega8) ADC for low voltage 
> > measurements
> > 
> > 
> > I need to measure voltages in the 0-50mV range. I suspect the answer 
> > here is to use an amp to get this to a more reasonable level (say
> > 0-2.5V) however I was wondering if it is ok to just supply AREF to 0.1
> 
> > volts.. I suspect this is a bad idea, but I wanted to know for sure.
> > 
> > thanks
> > 
> >  - jim
> > 
> > 
> > 
> >  
> > Yahoo! Groups Links
> > 
> > 
> > 
> >  
> > 
> > 
> > 
> 
> 
> 
> 	
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