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Calculating resolution.

Mymla

May 4, 2015
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Hey everyone,
could anyone point me in the right direction to working out this question. I have the answer but not sure how to work it out of the question.

Calculate the resolution the following convert given that Vref=5V.

8 Bit


Answer: 19mV

Is this a correct formula to use? (Vin/Vref) * 2^bitdepth
 

Arouse1973

Adam
Dec 18, 2013
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Hello. How I do it is this 5/((2^8)-1) and that gets me pretty much the same answer as you. :)
Thanks
Adam
 

dorke

Jun 20, 2015
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Adam,
You shouldn't subtract 1.
To convince yourself check the case of 1 bit ;)
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
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Adam,
You shouldn't subtract 1.
To convince yourself check the case of 1 bit ;)
Oddly enough that was the same argument I used to convince myself that you must subtract 1.
 

dorke

Jun 20, 2015
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Oddly enough that was the same argument I used to convince myself that you must subtract 1.

I can understand why.

For 1 bit we have 2 states "0" and "1".
How do we decide which state are we in?
"0" if we are below 1/2
"1" if we are above 1/2

What is the resolution than?
I would say 1/2 not 1...;)

untitled.JPG
 

Arouse1973

Adam
Dec 18, 2013
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Um I used to do it the other way and then I read on some website a time a go you should subtract 1. I am not saying your wrong...let me see if I can find the website.
Cheers
Adam
 

Arouse1973

Adam
Dec 18, 2013
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Not the website I saw but he mentions -1. But I think where I might be wrong is the maximum value FSD is Vref -1bit of resolution? Is that correct?
Adam
 

dorke

Jun 20, 2015
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Adam,
Actually you are correct my bad.

The definition of resolution is "the value that 1LSB equals to".
In the case of 1bit it is indeed 1.
so ,subtraction of 1 is the correct way to calculate the resolution.

Another value is the "error" of a converter this is 1/2 LSB
no -1 here.
 
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