Issue No. 08 - August (1985 vol. 34)
R. Gnanasekaran , Department of Electrical Engineering and Computer Science, University of Nevada
A fast serial-parallel (FSP) multiplier design is derived from the carry-save add-shift (CSAS) multiplier structure. The CSAS technique accepts multiplier bits serially (lsb first) and produces outputs serially (lsb first). Multiplication of two n bit unsigned numbers requires 2n clock cycles to complete the process out of which n clocks are used for n-row carry-save additions, and the other n clocks are utilized only to propagate the remaining carries. This CSAS structure is modified so that it operates as a CSAS unit for the first n clocks and reconfigures itself as an n bit ripple-carry parallel adder at the (n + 1)st clock, thus allowing the carries to ripple through, eliminating the delay due to storage elements during the last n clocks. It is shown that this modification results in an about one-third increase in speed for an approximately one-third increase in hardware. The technique is extended to signed numbers represented in 2's complement form. Also, it is shown how these implementations can be modularized.
2's complement multiplication, Add-shift multiplier, array multiplier, carry-save addition, pipeline multiplier, ripple-carry parallel adder, serial-parallel multiplier
R. Gnanasekaran, "A Fast Serial-Parallel Binary Multiplier", IEEE Transactions on Computers, vol. 34, no. , pp. 741-744, August 1985, doi:10.1109/TC.1985.1676620