Probably my question is a bit old topic, but recently I found I may not understand it clearly. Let's take the bottom-plate sampling SARADC as the example, the binary-weighted is 2^N, N is integer. If we look at 5-bit SARADC, the capacitor array is 2^4 + 2^3 + 2^2 + 2^1 + 2^0 = 16 + 8 + 4 + 2 + 1 = 31, if we add the dummy LSB cap in the cap array, we have 32 unit caps in the cap array. That is what I understand the binary-weighted SARADC for bottom-plate sampling.
However, recently, I saw a SARADC without the dummy LSB cap in the cap array, and it is bottom-plate sampling, the designer explains the binary-weighted means as long as the caps in the cap-array are binary-weighted, then it is called binary-weighted SARADC. I am thinking if we don't have the dummy LSB cap, can we really achieve the LSB based on the binary-weighted calculation?
By the way, in the top-plate sampling, due to the parasitic cap in the cap-array, we can reuse the parasitic cap as the dummy LSB cap based on my understand, but not for the bottom-plate sampling.
Any comments or suggestions on my confusion? Please correct me if I misunderstand the binary-weighted cap array in the SARADC.