ADC

Thread Starter

Cerkit

Joined Jan 4, 2009
287
What is the use of multiple channels on an ADC.I'm trying to understand how it works. Is the number of bits per channel to do with the resolution hence meaning it can sample along a larger scale of values?? Also does more channels mean more samples from one signal input or more samples from different signal inputs??
 

mik3

Joined Feb 4, 2008
4,843
More analog inputs means you can select which input you want to sample at a time. Thus you can sample many analog signals with the same ADC but not at the same time (each one input individually).
 

davebee

Joined Oct 22, 2008
540
yep.

The ADC itself is designed to convert a signal to some number of bits resolution. You give the ADC a "convert" signal, wait until it signals you that it is finished, then you read some number of bits out of it. You can repeat this continuously if you want.

Usually you use the smallest number of bits as you need, because all else being equal, more bits cost more and convert more slowly.

Some ADCs can convert really fast, like less than a microsecond, and some are really slow, like a tenth of a second per conversion.

Multiple channels are like a switch in front of one converter. First you tell the ADC which channel to use, then you perform a conversion and read the results. Each channel is connected to a separate pin on the chip. You're free to connect more than one pin to a single source but it wouldn't do anything extra for you. Usually the channel pins are connected to different sources.

Some converters are able to configure multiple pins as differential inputs, where one conversion converts the difference between two pins.
 

Thread Starter

Cerkit

Joined Jan 4, 2009
287
So how many bits do you suggest for sampling a dc signal varying from 0 to 5V. Or can I calculate a minimum/optimum??
 

beenthere

Joined Apr 20, 2004
15,819
Guess you don't like to do math. 8 bits resolves 256 levels. 9 bits would resolve 512, but isn't standard. So 10 bits gives 1024 levels. 5/1024 = 4.8 mv per bit.
 

italo

Joined Nov 20, 2005
205
where do you get 4.8mv I don't get it unless i asume that you use a 10v reference supose there is a 5 v ref then you are wrong in essence. I know he calls it channels but i better understand the word mutiplexing. there such things as dual ramp A/D too.
 
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