Synthesis of Arithmetic Circuits: FPGA, ASIC and Embedded Systems

9.3 ASIC DESIGNS

Application-specific integrated circuits (ASICs) refer to those integrated circuits specifically built for preset tasks. Why use an ASIC solution instead of another off-the-shelf technology—programmable logic device (PLD, FPGA), or a microprocessor/microcontroller system? There are, indeed, many advantages in ASICs with respect to other solutions: increased speed, lower power consumption, lower cost (for mass production), better design security (difficult reverse engineering), better control of I/O characteristics, and more compact board design (less complex PCB, less inventory costs). However, there are important disadvantages: long turn-around time from silicon vendors (several weeks), expensive for low-volume production, very high NRE cost (high investment in CAD tools, workstations, and engineering manpower), and, finally, once committed to silicon the design cannot be changed.

Application-specific components can be classified into full-custom ASICs, semi custom ASICs, and field programmable ICs (Figure 9.10). This latter, sometimes referred to as programmable ASICs, will be analyzed in Section 9.4: programmable logic.

9.3.1 Full-Custom ASIC

In a full-custom ASIC all mask layers are customized (Figure 9.11). Full-custom designs offer the highest performance and the smallest die size, with the disadvantages of increased design time, higher complexity and costs, together with the highest risk of failure. This design option only makes sense when neither libraries ...