How charge redistribution takes place in this switched capacitor DAC?
A was at 0V (connected to ground through Sc) before sampling began, and the bottom sides of all of the capacitors were at Ain. If the bottom sides of all of the capacitors are brought down to 0V by closing S1-S4, but the voltage across them stays the same (there's no circuit to discharge them), A must come down by the same amount, to -Ain.