High Performance Transfer Gate Circuit to Implement Incrementer/ Decrementer Function
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
Transfer gates and simple primitive logic can be configured to provide a circuit which will increment/decrement a count by one. The disclosed circuits provide this function using only one pair of transfer gates, an inverter and an exclusive-OR per bit. These realizations result in reduced area and improved overall performance. Fig. 1 illustrates the truth table for the decrement-by-1 function. The Boolean equation for the Carry-out (borrow) is Cout = Cin OR A. The Boolean equation for the decremented bit output is Zn = A XNOR Cin. (Image Omitted) Fig. 2A illustrates a single-bit circuit to implement the Carry- out (borrow) function using two transfer gates and an inverter. Fig.