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1/2 LSB what that means ?

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mengghee

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what does lsb mean accuracy

recently i have come across the 1/2 lsb in my instrumentation class and i am actually wondering what does that actually mean. something to do with ADC ?


regards,
mengghee
 

Hi mengghaee
1/2 LSB is the best (or ideal) accuracy which an ADC can inherently produce.
for example suppose equivalent output value must be 120.49, if output digit is 120 or 121 both of them are correct,
or in case of 120.99 if output is 120 we have 1 LSB error, however digit 120 are acceptable.
as you can see, if output value is 120 for 120.00-120.49 and 121 for 120.50-120.99 we have 0.5 LSB error.

Regards,
Davood.
 

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    mengghee

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so basicly, it means it is half a bit error ? i am doing an exam question saying that the common mode voltage for a bridge is 2v and this must contribute no more than 1/2 LSB. what does it mean if the common mode error cannot be more than 1/2 LSB and in a 5V 8 Bit ADC... how does it relate ? thank you.


regards,
mengghee
 

1/2 LSB is the ambiguious or maximum step error that can be tolerated in analog-to-digital conversion.

In a 5V 8-bit ADC, per quantisation level is 5V/8-bit or 0.0195V, thus 1/2 LSB is 1/2 of 19.5mV or 9.75mV.

From your exam question, it simply says that the 2V common-mode voltage can only have a common-mode voltage error that does not exceed 9.75mV.
 

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    mengghee

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