Carry lookahead adder

Details Carry lookahead adder Carry lookahead adder

1997-12-29

1999-09-14

Mai, Tan V.

Electrical computers: arithmetic processing and calculating

Electrical digital calculating computer

Particular function performed

708702, 708704, G06F 750

Patent

active

059516313

ABSTRACT:
A high-performance carry lookahead adder (CLA) which can reduce the delay time of the whole adder by constructing a carry generator used therein with NMOS logics, thereby effecting a high-speed operation of the adder along with a lower power-consumption. The carry generator receives an exclusive-OR value P(i, i=1,2,3,4) and a logic product value G(i) of two data, and an initial carry value C(1), and performs a function of G(4)+P(4).multidot.G(3)+P(4).multidot.P(3).multidot.G(2)+P(4).multidot.P(3 ).multidot.P(2).multidot.G(1)+P(4).multidot.P(3).multidot.P(2).multidot.P(1 ).multidot.C(1) to output a final carry value C(5). The carry generator includes a first NMOS transistor for executing an operation of P(4).multidot.G(3), second and third NMOS transistors for executing an operation of P(4).multidot.P(3).multidot.G(2), fourth to sixth NMOS transistors for executing an operation of P(4).multidot.P(3).multidot.P(2).multidot.G(1), seventh to eleventh NMOS transistors for executing an operation of P(4).multidot.P(3).multidot.P(2).multidot.P(1).multidot.C(1), and twelfth to fourteenth NMOS transistors for outputting the final carry signal C(5) by an OR operation of the respective logic product terms.

REFERENCES:
patent: 4899305 (1990-02-01), Needles
patent: 4962471 (1990-10-01), Cornelissen
patent: 5434810 (1995-07-01), Goto et al.
patent: 5500813 (1996-03-01), Song et al.
patent: 5719803 (1998-02-01), Naffziger

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