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# Minimum Voltage An ADC can measure

Hi,

How to determine the minimum voltage an ADC can measure.

What are the analysis we need to do for the same?

How to do the error budgeting of an ADC.

Regards

Hari

• Hello Hari,

Minimum voltage will be determined by the ADC resolution.  A 24-bit ADC can discern a much smaller voltage step than a 12-bit ADC.  Perhaps a more useful approach would be to define the voltage you need to measure/resolve, the voltage range of the signal, then we can determine both the ADC architecture (SAR or DELSIG) and number of bits.  This App Note should be very helpful in your determination: www.ti.com/lit/an/sloa249/sloa249.pdf .

This training presentation will also be helpful: TI Precision Labs - ADCs .  And on this ADC Support Link: www.ti.com/product/ADS1281/support , scroll down to the "Introduction to "Designing with Delta-Sigma ADCs" Training Series and view this as well.

At your service,

~Leonard

• In reply to LeonardEllis:

Hi Hari,

Just to add to Leonard's response...

Lower resolution ADC's will be limited by quantization error (or the resolution of the ADC). In this case the LSB size of the output code is the minimum resolvable signal. This is usually calculated as the the full-scale range divided by the total number of codes or: FSR/2^N, when "N" is the resolution of the ADC, given as the number of bits.

Higher resolution ADC's (around 16-bits and above) will be limited by thermal noise. When this is the case, you'll normally see that the noise table in the datasheet does not show a perfect 16 or 24-bit resolution (or "ENOB"). Instead, the datasheet will tell you the input-referred noise of the ADC, which is the same as the minimum voltage that the ADC can measure, since your input signal must be equal to or greater than the noise to be distinguishable from the noise.

Error budgeting on the other hand, usually deals with much more than just the ADC's noise...It will include the ADC's offset, offset drift, gain error, gain error drift, and linearity (INL). You can see an example of an error budget that I did here: e2e.ti.com/.../2075878

Best regards,
Chris

Christopher Hall
Applications Engineer | Precision Delta-Sigma Converters

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