To perform the subtraction of binary numbers with more than one bit, we have to use the Parallel Subtractors. This parallel subtractor can be designed in several ways, including combination of half and full subtractors, all full subtractors, all full adders with subtrahend complement input, etc.
The below figure shows a 4 bit Parallel Binary Subtractor formed by connecting one half subtractor and three full subtractors.
In this subtractor, 4 bit minuend ‘A3 A2 A1 A0‘ is subtracted by 4 bit subtrahend ‘B3 B2 B1 B0‘ and the result is the difference output ‘D3 D2 D1 D0‘ . The borrow output of each subtractor is connected as the borrow input to the next subtractor.