Tags: ADC, education, LSB, least significant bit, theory

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          For an ADC, a value of the LSB is calculated as follows:

 

LSB equation

 

where N is a number of bits. “Input voltage range” is the difference between maximum and minimum voltage values that ADC is able to convert. “Input voltage range” may be rail-to-rail and equal to VDD – VGND.

 

          Fig. 37 presents the transfer response of an ideal 3-bit ADC. Using the given definition of LSB, the LSB for the ADC is equal to:

 

LSB - 3-bit example

 

          Thus, one least significant bit LSB is equal to an analog value of 0.5 V:

 

1 LSB  =  0.5 V

 

LSB 3-bit plot

Figure 37: Transfer curve of an ideal 3-bit ADC, where power supply VDD is equal to 4V.