Efficient carry select adder using 0.12µm technology for low power applications

In the design of Integrated circuit area occupancy plays a vital role because of increasing the necessity of portable systems. Carry Select Adder (CSLA) is a fast adder used in data-processing processors for performing fast arithmetic functions. From the structure of the CSLA, the scope is reducing the area of CSLA based on the efficient gate-level modification. In this paper 16 bit, 32 bit, 64 bit and 128 bit Regular Linear CSLA, Modified Linear CSLA, Regular Square-root CSLA (SQRT CSLA) and Modified SQRT CSLA architectures have been developed and compared. However, the Regular CSLA is still area-consuming due to the dual Ripple-Carry Adder (RCA) structure. For reducing area, the CSLA can be implemented by using a single RCA and an add-one circuit instead of using dual RCA. Comparing the Regular Linear CSLA with Regular SQRT CSLA, the Regular SQRT CSLA has reduced area as well as comparing the Modified Linear CSLA with Modified SQRT CSLA; the Modified SQRT CSLA has reduced area. The results and analysis show that the Modified Linear CSLA and Modified SQRT CSLA provide better outcomes than the Regular Linear CSLA and Regular SQRT CSLA respectively. This project was aimed for implementing high performance optimized FPGA architecture. Modelsim 10.0c is used for simulating the CSLA and synthesized using Xilinx PlanAhead13.4. Then the implementation is done in Virtex5 FPGA Kit.

Carry select adder (CSLA) one of the fastest adders used in complex data processing to perform fast arithmetic functions. Minimum amount of power consumption is a major driving force behind the development of CMOS technologies. From the structure of CSLA it is clear that there is scope for reducing the area & power consumption in the CSLA. In this paper 8T full adder is used as a building block for 8-bit SQRT CSLA. 8T full adder is designed by XNOR-XNOR hybrid CMOS design. Based on this modification, 8-, 16-, 32-, 64-bit SQRT CSLA architecture has been developed & compared with the regular SQRT CSLA. Binary to Excess one converter (BEC) based CSLA are analyzed to study the data dependence & to identify all redundant logic operations. In this paper, all the redundant logic operations in the conventional CSLA are eliminated and a new logic formulation where carry select operation is scheduled before the calculation of final sum is proposed. Gate Diffusion Input (GDI) technique of low power digital combinatorial circuit design is also described. The frequency of operation is 5 MHZ. This work estimates the performance of the proposed design with the regular design in terms of area & power through the logic design & layout in 250nm CMOS process technology & implemented using Tanner (S-Edit) tool. The result analysis shows that the proposed structure is better than the conventional CSLA.

Adders are digital circuits that perform addition operation. There are various types of adder structures such as Ripple carry adder (RCA), carry look ahead adder (CLA) , carry select adder (CSLA) , carry save adder(CSA), carry skip adder, carry increment adder and so on. Again CSLA is of two types that is linear carry select adder (LCSLA) & square root carry select adder (SQRT CSLA). To design an efficient adder circuit in terms of area, power and speed is one of the challenging task in modern VLSI design field. In this paper performance analysis of different adder structures like RCA, CLA, LCSLA and SQRT CSLA has been carried out and then a Heterogeneous adder structure is proposed, which compose of four different sub homogeneous adders (RCA, CLA, LCSLA and SQRT CSLA). The heterogeneous adder structure is used to demonstrate the tradeoffs between the speed and area. In this paper, all adder structures i.e., RCA, CLA, LCSLA and SQRT CSLA are to be designed and are to be compared with each other in terms of delay and area. Then by using the homogeneous adder structures different heterogeneous adder structures of 16-bit size are to be designed. Different heterogeneous adder architectures are compared with each other in terms of delay (ns) and area (number of LUTs). All the adder structures are designed using VHDL with the help of ISE Xilinx design suite 14.2 and functionally simulated using ISIM simulator. All the designs are to be synthesized using Xilinx XST synthesizer.

In electronic applications, better performance of the digital systems can be achieved using a faster adder circuit. This paper shows a modified carry-select adder (CSA) architecture which has low power and reduced area compared to the regular CSA. This high speed CSA is achieved by replacing the existing binary to excess-1 converter (BEC-1) with D-latch enabled CSA. Regular square-root CSA (SQRT CSA) architectures have also been developed and compared with the proposed BEC-1 D-latch enabled CSA. This work evaluates the performance of delay, area, power, and their products for existing and proposed CSA designs. This shows that proposed D-latch CSA structure is better than the regular and modified SQRT CSA and existing Ripple CSA. The proposed CSA architecture requires approximately 86 % fewer gates and 77 % shorter delay than the original CSA designs.

In this paper, a new carry select adder (CSLA) architecture is proposed with a lower area and a higher speed compared to previous CSLAs. The proposed CSLA is a low-area and high-speed design utilizing a new add-one circuit that is used instead of the second ripple carry adder (RCA) with the input carry equal to one (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</sub> =1) inside each group of the basic CSLA. Moreover, to expedite the add operation, a new grouping structure is proposed instead of the basic square-root (SQRT) grouping as well as utilizing a faster RCA in each group. Despite the fact that the proposed CSLA has not attained the lowest power consumption among all existing designs based on the PDK 45nm standard cell library, but it has achieved the lowest area and delay compared to previous CSLAs. Implementation results show that 8 to 33% area reduction and 12 to 44% speed improvement are achieved in the proposed CSLA compared to previous designs.

Computational speed of basic data path elements such as adders plays a crucial role in performance of digital and signal processing systems. Among various adder architectures, carry select adder (CSLA) has better performance in terms of speed in comparison with others. However, this merit is accompanied by its high power dissipation and area occupancy due to redundant computing elements used in each stage hence limiting its application. Power dissipation in these adders can be minimized by various low power implementation techniques such as reversible logic gates, multi-V th approach, and adiabatic logic. Among these low power approaches, adiabatic logic proves to be more efficient in comparison with other low power approaches. In the proposed work, 180 nm CMOS technology in CADENCE environment is used to carry out the design and analysis of both conventional and proposed CSLA architectures. Power dissipation in this proposed 8-bit CSLA architecture reduces by about 82% as compared to conventional 8-bit CSLA adder architecture. Further, the computational delay is also reduced when compared with the conventional 8-bit CSLA architecture. It is noteworthy that delay in adiabatic logic circuits greatly depends on frequency of operation [1].

Based on the idea of sharing two adders used in the carry select adder (CSA), a new design of a low-power high-performance adder is presented. The new adder is faster than a ripple carry adder (RCA), but slower than a CSA. On the other hand, its area and power dissipation are smaller than those of a CSA.

Adders are the most important fundamental blocks of the digital systems which are used in a wide variety of applications. Among them the first basic adder is the Ripple Carry Adder (RCA) and the fastest adder is the Carry Select Adder (CSA). Though all these adders are existed, the speed adding using low power and optimized area is still a challenging issue. In this paper a new technique, Modified Gate Diffusion Input (MOD-GDI) is used to achieve an optimized design with less transistor count and low power dissipation. In the proposed work the 8-bit, 16-bit Ripple Carry Adder and the 8-bit, 16-bit Carry Select Adder have been designed using the CMOS and MOD-GDI techniques. The comparison of their power dissipations and overall transistor count is done and proved that low power and optimized designs are achieved through MOD-GDI technique. The simulation is carried out using Mentor Graphics tool with a supply voltage of 1.8 V at 90 nm technology.

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.

A multiplier is one of the key hardware blocks in most digital and high performance systems such as FIR filters, micro processors and digital signal processors etc. A system's performance is generally determined by the performance of the multiplier because the multiplier is generally the slowest element in the whole system and also it is occupying more area consuming. The Carry Select Adder (CSLA) provides a good compromise between cost and performance in carry propagation adder design. A Square Root Carry Select Adder using RCA is introduced but it offers some speed penalty. However, conventional CSLA is still area-consuming due to the dual ripple carry adder structure. In the proposed work, generally in Wallace multiplier the partial products are reduced as soon as possible and the final carry propagation path carry select adder is used. In this paper, modification is done at gate level to reduce area and power consumption. The Modified Square Root Carry Select-Adder (MCSLA) is designed using Common Boolean Logic and then compared with regular CSLA respective architectures, and this MCSLA is implemented in Wallace Tree Multiplier. This work gives the reduced area compared to normal Wallace tree multiplier. Finally an area efficient Wallace tree multiplier is designed using common Boolean logic based square root carry select adder.

Multipliers are important hardware components in most digital and high-speed systems, such as microprocessors, digital signal processors, and FIR filters. In reality, Multipliers, which are complicated units, are responsible for the total speed, size, and power consumption of digital systems. Multiplication in digital systems has a wide range of requirements for speed, size, power consumption, and other parameters. It comprises of partial product production, partial product reduction, and lastly carry-propagate addition. The Multiplier design focuses on minimizing power dissipation while still maintaining other parameters. To obtain considerable power savings in VLSI design, the dynamic power dissipation of multipliers must be reduced. The fundamental goal of this effort is to choose an appropriate adder that consumes less power, runs at a high speed, and is plainly less expensive. The available 8-bit adders, such as the Carry Select Adder, Ripple Carry Adder, Carry Look Ahead Adder, and Kogge Stone Adder, are investigated. Among the adders tested, the Kogge Stone Adder performs the best. This adder may be used to create efficient multipliers.

ABSTRACTAn ultra-low-power, 55-transistor 8-bit priority encoder is proposed, based on a modified n-type dynamic scheme using feedback from higher- to lower-priority outputs. A comparative study, including other designs from literature, is performed on transistor level at 32 and 45 nm predictive technology. The simulation results showed that, compared to the other examined works, the proposed circuit achieves reduction in power dissipation as high as 88% and reduction in power delay product, up to 93.0% while having the smallest transistor count. It is thus proved to be an all-around efficient design in terms of power, performance and area.

본 논문에서는 고속 병렬 곱셈기에서 속도향상을 위해 부분 곱을 가산하는 과정에 구성되는 CSA(Carry Select Adder) 트리에 새로운 압축기를 적용한 새로운 첫 번째 부분 곱가산(First Partial Product Addition : FPA)를 제안하여 기존의 전가산기를 이용한 병렬가산기보다 부분곱을 계산하는 속도를 약 20% 개선할 수 있게 했다. 새로운 회로는 새로운 FPA 구조를 사용하여 최종 합 CLA 비트를 N/2로 줄인다. 2.5v 0.25um CMOS 기술을 이용하여 제작된 16<TEX>${\times}$</TEX>16 곱셈기는 5.14nS의 곱셈 고속을 얻었다. 이 곱셈기의 구조는 파이프라인 설계에 용이하며 고성능을 낸다. In this paper, we proposed a new First Partial product Addition (FPA) architecture with new compressor (or parallel counter) to CSA tree built in the process of adding partial product for improving speed in the fast parallel multiplier to improve the speed of calculating partial product by about 20% compared with existing parallel counter using full Adder. The new circuit reduces the CLA bit finding final sum by N/2 using the novel FPA architecture. A 5.14nS of multiplication speed of the <TEX>$16{\times}16$</TEX> multiplier is obtained using <TEX>$0.25\mu\textrm{m}$</TEX> CMOS technology. The architecture of the multiplier is easily opted for pipeline design and demonstrates high speed performance.

This paper deals with low power multiplier design that plays a significant role in green wireless communications systems. Over the period of time, researchers have proposed various multiplier designs in order to get high speed. Vedic multiplier is considered as one of the low power multiplier along with high speed as compared with traditional array and booth multipliers. Vedic Multiplier contains a total of sixteen algorithms/sutras for predominantly logical operations. This research focuses on thermal aspects and energy efficiency of wireless communications systems with the thermal aware low power design of Vedic Multiplier. Temperature plays an important role on the performance of any device. The primary purpose of this research is to enhance the thermal stability of the wireless communications. Energy efficient IO standards are used to decrease the power dissipation of Vedic Multiplier and that eventually decrease power dissipation of wireless communications systems. In order to study the effect of different process technology (40, 65, 90 nm) on our design, a novel design is implemented on 40, 65 and 90 nm based FPGA. In this work, we are integrating thermal aware design approach for energy efficient Vedic Multiplier on various FPGA using LVCMOS and HSTL I/O standard. LVCMOS is an acronym for Low Voltage Complementary Metal Oxide Semiconductor and HSTL is an acronym for High Speed Transceiver Logic. In this Vedic Multiplier, we are using three LVCMOS I/O standard and nine HSTL I/O standard. In order to test the thermal sustainability of our Vedic Multiplier design, we are testing it in three different room temperatures i.e. 20, 30, and 40 °C. Using LVCMOS25, there is 12.99, 19.23 and 10.28% reduction in power dissipation on 90, 65 and 40 nm FPGAs respectively. For LVCMOS25, when our Vedic Multiplier design is migrated from 40 nm design to 90 nm FPGA design, there is 87.72% reduction in power dissipation of Vedic Multiplier when temperature is kept constant at 20 °C. When temperature is scaled down from 50 to 20 °C there is 12.45, 14.93, 12.84, 9.45 and 8.48% saving in power dissipation on using HSTL_I, HSTL_I_12, HSTL_I_18, HSTL_I_DCI and HSTL_I_DCI_18 IO Standard respectively on 90 nm FPGA.

Since miniaturization of CMOS has taken place, speed and power are the most important parameters for any circuit, like speed of an adder is a critical parameter in the overall performance of an Arithmetic Logic Unit (ALU). In order to identify the best suitable 2-bit adder in terms of speed, power dissipation, area and leakage current acomparative study of five different kinds of standard 2-bit adder architectures, Ripple Carry (RCA), Carry Look ahead (CLA), Manchester Carry Chain (MCC), Carry Select (CSL) and Kogge Stone (KSA) adders has been done in this paper.The adders are re-designed, implemented and analyzed at supply voltages ranging from 0.6 - 1 V on 28nm CMOS Technology to improve the speed and power. Simulation results for the different adders show that MCC at 0.6V is 32.4% faster than RCA and 15.6% faster than CLA. RCA having minimum transistor count has the least power dissipation and CLA gives minimum leakage current for lower supply voltages, but as the supply voltage increases MCC produces the least leakage current.