The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Dec. 26, 1989
Filed:
Mar. 31, 1988
Henry M Darley, Plano, TX (US);
Texas Instruments Incorporated, Dallas, TX (US);
Abstract
A signed digit adder (10) includes a plurality of cells (12) which input signals X.sub.s, X.sub.m, Y.sub.s, Y.sub.m, R.sub.-1 and U.sub.-1, where X.sub.s and X.sub.m are the sign and magnitude bits of one digit of a signed bit representation. Similarly, Y.sub.s and Y.sub.m are the sign and magnitude bits of the second operand. R.sub.-1 and U.sub.-1 are signals received from the preceding cell (12). Each cell outputs R and U bits, and the sum bits Z.sub.s and Z.sub.m. Each cell (12) comprises function blocks (14-26) which determine the outputs from the given inputs. Function block (14) determines the output R as NOT(X.sub.s +Y.sub.s). Function block (20) determines the output U=E.multidot.NOT(R.sub.-1)+NOT(E).multidot.NOT(Q) where Q=(NOT (X.sub.s)+NOT (Y.sub.s)).multidot.X.sub.m. The determination of Q is performed in function block (16). Function block (24) determines the output Z.sub.s =U.sub.-1 .multidot.T and function block (26) determines the output Z.sub.m =U.sub.-1 XOR (NOT (T)). T is determined in function block (22)=E XOR (NOT (R.sub.-1)). E is determined in function block (18) as X.sub.m XOR Y.sub.m. Function blocks (14-26) are optimized for speed relative to the temporal validity of the inputs.