Help me find DAC Output function
With the 8C/7 capacitor splitting the the array in half, the total value of the left block of capacitors is made equal to the right block LSB-only capacitance by the inclusion of the series capacitor. Does this help?

C + C + 2C + 4C +8C/7 = C (LSB of right hand block)

This means that the left block LSB capacitor is weighted down appropriately.

Here's an interesting document on the theory. I was a bit disappointed more documents were not avaiable.