Search Results (7)

We introduce a new carry look-ahead adder (NCLA) architecture that employs non-uniform-size carry look-ahead adder (CLA) modules, in contrast to the conventional CLA (CCLA) architecture, which utilizes uniform-size CLA modules. We adopted two strategies for the implementation of the NCLA. Our novel approach enables improved speed and energy efficiency for the NCLA architecture compared to the CCLA architecture without incurring significant area and power penalties. Various adders were implemented to demonstrate the advantages of NCLA, ranging from the slower ripple carry adder to the widely regarded fastest parallel-prefix adder viz. the Kogge–Stone adder, and their performance metrics were compared. The 32-bit addition was used as an example, with the adders implemented using a semi-custom design method and a 28 nm CMOS standard cell library. Synthesis results show that the NCLA architecture offers substantial improvements in design metrics compared to its high-speed counterparts. Specifically, an NCLA achieved (i) a 14.7% reduction in delay and a 13.4% reduction in energy compared to an optimized CCLA, while occupying slightly more area; (ii) a 42.1% reduction in delay and a 58.3% reduction in energy compared to a conditional sum adder, with an 8% increase in the area; (iii) a 14.7% reduction in delay and a 37.7% reduction in energy compared to an optimized carry select adder, while requiring 37% less area; and (iv) a 20.2% reduction in energy and a 55.4% reduction in area compared to the Kogge–Stone adder. Full article

The carry look-ahead adder (CLA) is well known among the family of high-speed adders. However, a conventional CLA is not faster than other high-speed adders such as a conditional sum adder (CSA), a carry-select adder (CSLA), and the Kogge–Stone adder (KSA), which is the fastest parallel-prefix adder. Further, in terms of power-delay product (PDP) that characterizes the energy of digital circuits, the conventional CLA is not efficient compared to CSLA and KSA. In this context, this paper presents a high-speed and energy-efficient architecture for the CLA. Many adders ranging from ripple carry to parallel-prefix adders were implemented using a 32-28 nm CMOS standard digital cell library by considering a 32-bit addition. The adders were structurally described in Verilog and synthesized using Synopsys Design Compiler. From the results obtained, it is observed that the proposed CLA achieves a reduction in critical path delay by 55.3% and a reduction in PDP by 45% compared to the conventional CLA. Compared to the CSA, the proposed CLA achieves a reduction in critical path delay by 33.9%, a reduction in power by 26.1%, and a reduction in PDP by 51.1%. Compared to an optimized CSLA, the proposed CLA achieves a reduction in power by 35.4%, a reduction in area by 37.3%, and a reduction in PDP by 37.1% without sacrificing the speed. Although the KSA is faster, the proposed CLA achieves a reduction in power by 39.6%, a reduction in PDP by 6.5%, and a reduction in area by 55.6% in comparison. Full article

Nowadays, floating point multiplier (FPM) plays an essential role in computers. The IEEE 754 norm for floating point numbers is the most widely recognized portrayal for real numbers on today’s PCs. Addition, multiplication, subtraction, and division are the four important functions of single precision floating arithmetic, amongst which multiplication has the most extensive use in every algorithm. Fast multipliers are of critical need in modern high-performance applications, especially in digital signal processing, because DSP involves many important multiplication-based operations, e.g., fast Fourier transform (FFT) and convolution. These speedy computations can be implemented on field programmable gate arrays (FPGAs), because they can provide a high speed and a large number of on-board digital resources. FPGAs are involved in many modern applications such as cryptography and communication computations, arithmetic and scientific computation, digital image and signal processing, etc. There are many forms of FPM available. This paper describes an efficient way to implement single precision FPM in IEEE 754 standard format, where Verilog hardware description language (VHDL) is used to implement the design for Xilinx Spartan 6 FPGA. Here, the 32-bit number will be divided into three parts: sign bit, exponent, and mantissa. This paper is implemented by using different types of adders, which includes carry increment adder (CIA), carry select adder (CSA), ripple carry adder (RCA), and carry look-ahead adder (CLA). Carry save array (CSA) multiplication is used for performing the mantissa multiplication. Full article

Ripple-carry adder (RCA) is among the most common type of adder. However, it is not preferred in many applications because of its high latency. In this paper, two architectures of high-speed parallel RCA (PRCA) along with fault detection and localization are proposed, with reduced overhead as compared with carry look-ahead adder (CLA). In the proposed approach, RCA is divided into blocks, where the initial carry input for each block will be generated by a carry look-ahead logic unit. The delay is reduced by 43.81% as compared with the conventional 64-bit RCA design. The delay is further reduced by replacing the last blocks with a single RCA-based CSeA design and becomes equal to CLA if the last three blocks are replaced with CSeA. The proposed 64-bit design of PRCA and PRCA-CSeA requires 20.31% and 22.50% area overhead as compared with the conventional RCA design. Whereas, the delay-power-area product of our proposed designs is 24.66%, and 30.94% more efficient than conventional RCA designs. With self-checking, the proposed architecture of PRCA and PRCA-CSeA with multiple-fault detection requires 42.36% and 44.35% area overhead as compared with a 64-bit self-checking RCA design. Full article

Addition is a fundamental operation in microprocessing and digital signal processing hardware, which is physically realized using an adder. The carry-lookahead adder (CLA) and the carry-select adder (CSLA) are two popular high-speed, low-power adder architectures. The speed performance of a CLA architecture can be improved by adopting a hybrid CLA architecture which employs a small-size ripple-carry adder (RCA) to replace a sub-CLA in the least significant bit positions. On the other hand, the power dissipation of a CSLA employing full adders and 2:1 multiplexers can be reduced by utilizing binary-to-excess-1 code (BEC) converters. In the literature, the designs of many CLAs and CSLAs were described separately. It would be useful to have a direct comparison of their performances based on the design metrics. Hence, we implemented homogeneous and hybrid CLAs, and CSLAs with and without the BEC converters by considering 32-bit accurate and approximate additions to facilitate a comparison. For the gate-level implementations, we considered a 32/28 nm complementary metal-oxide-semiconductor (CMOS) process targeting a typical-case process–voltage–temperature (PVT) specification. The results show that the hybrid CLA/RCA architecture is preferable among the CLA and CSLA architectures from the speed and power perspectives to perform accurate and approximate additions. Full article

Adder is an important datapath unit of a general-purpose microprocessor or a digital signal processor. In the nanoelectronics era, the design of an adder that is modular and which can withstand variations in process, voltage and temperature are of interest. In this context, this article presents a new robust early output asynchronous block carry lookahead adder (BCLA) with redundant carry logic (BCLARC) that has a reduced power-cycle time product (PCTP) and is a low power design. The proposed asynchronous BCLARC is implemented using the delay-insensitive dual-rail code and adheres to the 4-phase return-to-zero (RTZ) and the 4-phase return-to-one (RTO) handshaking. Many existing asynchronous ripple-carry adders (RCAs), carry lookahead adders (CLAs) and carry select adders (CSLAs) were implemented alongside to perform a comparison based on a 32/28 nm complementary metal-oxide-semiconductor (CMOS) technology. The 32-bit addition was considered for an example. For implementation using the delay-insensitive dual-rail code and subject to the 4-phase RTZ handshaking (4-phase RTO handshaking), the proposed BCLARC which is robust and of early output type achieves: (i) 8% (5.7%) reduction in PCTP compared to the optimum RCA, (ii) 14.9% (15.5%) reduction in PCTP compared to the optimum BCLARC, and (iii) 26% (25.5%) reduction in PCTP compared to the optimum CSLA. Full article

In this paper, we analyze the variability of III-V homojunction tunnel FET (TFET) and FinFET devices and 32-bit carry-lookahead adder (CLA) circuit operating in near-threshold region. The impacts of the most severe intrinsic device variations including work function variation (WFV) and fin line-edge roughness (fin LER) on TFET and FinFET device I_on, I_off, C_g, 32-bit CLA delay and power-delay product (PDP) are investigated and compared using 3D atomistic TCAD mixed-mode Monte-Carlo simulations and HSPICE simulations with look-up table based Verilog-A models calibrated with TCAD simulation results. The results indicate that WFV and fin LER have different impacts on device I_on and I_off. Besides, at low operating voltage (<0.3 V), the CLA circuit delay and power-delay product (PDP) of TFET are significantly better than FinFET due to its better I_on and C_g,ave and their smaller variability. However, the leakage power of TFET CLA is larger than FinFET CLA due to the worse I_off variability of TFET devices. Full article