Carry Look-Ahead Address Using Static Pass Transistors
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
This arrangement combines ripple carry using pass transistors with carry look-ahead also using pass transistors producing a fast, yet simple, carry network for a parallel adder. As shown in Fig. 1, a chain of pass transistors propagates a carry to produce after each pass transistor a higher-order carry other than the next higher-order carry. Three mutually exclusive signals (Image Omitted) produce a higher-order carry Cb from a lower-order carry Ca via one pass transistor. Where: (Image Omitted) As shown in Fig. 2, the three control signals in Fig. 1 are themselves produced with static pass transistors. The number of carry look-ahead levels can be extended to two or more, as illustrated in Fig. 3, for a 64-bit carry using a 2-level carry look-ahead.