In an assignment, I need to find the settling Time of the ADC Input Circuit time to reach 1/4 of the LSB.
The ADC has 12 bits. I also know that C=12 pF and R=10 kohm. I found a formula that i used which worked:
t=-ln(1/(2^N*4))*τ where the 4 symbolizes the 4 in 1/4. N is the wordlength N=12 τ=RC=10*10^3*12*10^-12=1.2*10^-7. => t=1164.448 ns
Now the task is to use the 6 most significant bits, still with 1/4 of the LSB, C and R is the same. My original idea was to use the same formula but now with N=6. t=-ln(1/(2^6*4))*1.2*10^-7=665.421 ns
According to a correcting system this was wrong, so i don't have access to any correct answers.
What am i doing wrong here? How can i do right to find the settling time to reach 1/4 of the LSB when only using 6 most significant bits of a 12 bit ADC?
I see that the ADC is still a 12 bit system, so maybe that is where i am going wrong when i do N=6, changing the ADC to a 6 bit system. But still, i don't know how to specify the time calculation to just find the 6 most significant bits out of the 12.