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# 18bit ADC snr=93db is it good?

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#### allan_guo

##### Junior Member level 3
I think 18bit adc, SNR must be larger than 18*6.02+1.** may be better than 108db.is this ADC good?
the other question:INL(maxium)=2LSB, can this cause missing code?
I just see a datasheet:it says no missing code with INL=2LSB.I am confused.

A beginer in ADC, thanks everyone.

of course it is a good adc. only its snr is not very high.
for second, INL = 2LSB may be no missing code.

sunking said:
of course it is a good adc. only its snr is not very high.
for second, INL = 2LSB may be no missing code.

to sunking: INL=2LSB I think will cause missing code, can you explain?thanks very much

see attached

Having INL=2LSB does not necessarily cause missing codes. To check for missing codes you have to look for the DNL instead, and see if it is larger than -1.

Rgds

You have to see your design specification to find the snd requirement for your application. you must check your input signal's band of interest.
If your system needs 18bit of dynamic resolution then you have to go for 108dB SNR ADC.
Static performance like DNL mainly tells you about Missing code (DNL<+-1).
The reason behind the bad value of SNR is due to its larger INL.

### allan_guo

Points: 2
I see.thanks every one

Shaber_Mezbah said:
You have to see your design specification to find the snd requirement for your application. you must check your input signal's band of interest.
If your system needs 18bit of dynamic resolution then you have to go for 108dB SNR ADC.
Static performance like DNL mainly tells you about Missing code (DNL<+-1).
The reason behind the bad value of SNR is due to its larger INL.

Do you mean: when SNR is good ,then the INL is good.just like sunking's curve,the vout will come near to the ideal curve. that's the better the SNR,the vout will more like the ideal vout.

yeah.. as the name implies:
INL: integral non-linearity.

this non-linearity is also coming in SNDR (peoples usually call it SNR)

I doubt that. I think DNL implies SNR, and INL represents SDR, SFDR. In general, noise performance reflects in DNL, while distortion problems degrade INL.

Second, INL of 2 doesn't say anything about missing codes. Only |DNL| > 1 would cause missing codes.

The data sheet may mean the ratio of a full scale sine wave to all noise+distortion. This is the SNDR mentioned above.

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