6. High-Radix Arithmetic-Logic Unit (ALU) Based on Memristors

This chapter presents a novel method for implementing crossbar-based multi-level memories, where each cross-point cell stores multiple bits. Furthermore, a conceptual solution for novel CMOS-compatible, memristive, high-radix arithmetic logic units (ALUs) is proposed, for future computing systems. More specifically, a hybrid ALU circuit nano-architecture is described, where: (a) CMOS peripheral circuits are used for binary arithmetic operations; (b) a memristive reconfigurable crossbar-based memory block is used to: (i) allow parallel read/write of data; (ii) facilitate the implementation of efficient arithmetic algorithms (e.g. fast partial product creation for multiplication); and (iii) store information in a compact, high-radix form. Instead of single memristors, the crossbar nodes comprise a type of multi-state composite memristive switches, described in Chap. 3, which permit multi-bit storage in a more robust manner. Radix-4 representation is used because: (i) it balances the offered advantages with the peripheral binary conversion circuitry overhead; and (ii) it provides a good density/reliability trade-off. The fine operation and accuracy of the proposed system architecture is demonstrated through SPICE-level simulations.