If you are negating a single term you can't. If you are adding n terms using an adder tree, the 1 feeds to the carry in of the next level ( it is simply a conc

If you are negating a single term you can't. If you are adding n terms using an adder tree, the 1 feeds to the carry in of the next level ( it is simply a concatenation since the carry term is shifted left by 1). Only thw final carry propagate adder will have the add with 1.