Design Article
ADC 'accuracy' and 'resolution' are not the same
Mohit Arora, Freescale Semiconductor
5/3/2010 11:41 AM EDT
Analog-to-digital converters (ADC) are advertised as having "n" bit resolution, which often is misunderstood to mean accuracy.
Resolution does not imply accuracy nor does accuracy imply resolution.
Application determines if missing codes are allowed and degree of accuracy required.
This article illustrates some of the application examples to show significant difference between accuracy and resolution.
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slabs
5/6/2010 12:33 PM EDT
I am more confused after reading this paper. I dont remember learning that Dynamic range and SNR ratio are the same thing. Although both are system measurements made end to end after implementation. SNR ratio is a static measurement and quantification of the actual noise floor when compared to the theoretical maximum full scale output. Dynamic range on the otherhand is a dynamic measurement made with a signal present and is the ratio of smallest measurable change in the signalcompared to the maximum signal possible.
Now something for other readers to comment on. I remember someone saying to me once that because Dynamic Range is a dynamic end to end measurement it includes the effect of all other errors in the system and is therefore a valid expression of the accuracy, albeit I agree with the author that they are not the same thing.
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gustavob
5/15/2010 9:23 PM EDT
This article is good to alert the designer about how a bad specified parameter affects the whole system perfomance. But there's another degrating parameter to accuracy: the comparator's minimal diferencial voltage input. This is the minimal diference voltage |v+ - v-| between the inputs which the comparator distinguishes which one is greater or smaller. This limits from bellow the difference between vin and vref, |vin - Vref|/2^nbits, otherwise the ADC can't distinguish two consecutive codes. In conclusion the accuracy worsens.
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