ADC: Max error - where this 0.5 LSB limit originated ?

[alok_ky]

ADC: Max error

Hi

I noted that, in an ADC, when some inaccuracy creates any error, then this error is compared with the +/- 0.5 LSB value.
It is always commented that this error has to be less than 0.5LSB

From where this 0.5 LSB limit originated ?

Will all the ADC errors not get added to the +/- 0.5 LSB Quantization error ?

Please clarify.

 

[sivamit]

Re: ADC: Max error

Hi,
0.5 LSB is the maximum error value.
For instance,
-----------------------------------4
-------------------3.5 (=Vin) LSB=1V
-----------------------------------3
-----------------------------------2
-----------------------------------1

as shown above assume that your ADC can read only integers(1,2,3,4....etc)
If the actual input voltage(Vin) falls between these two ranges(b/w 3 & 4)
the ADC output will be..

if Vin=3.1-------------out=DIG 3V
3.2------------------DIG 3V
3.3 "
3.4 "
3.5------------for this case the output may be digital equvalent of 3v or 4.

Whatever it is,you will get only 0.5LSB error maximum... i.e for this case LSB=1 V
and 0.5LSB=0.5V

When Vin=3.6 u should not get 3V because this level falls on the 4V range.


Regards,
S