AVR-Chat

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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