The different types of parallelprefix adders available are Kogge-Stone adder, Brent- kung adder, Sklansky adder, Han-Carlson adder, Knowles adder and Ladner-Fischer adder. These adders offer a tradeoff among the number of stages of logic, the number of logic gates, fanout and amount of wiring between stages. Kogge-Stone adder, Brent- kung adder and Sklansky adder are the fundamental adders. Brent-Kung uses minimal number of computation nodes which yields in reduced area but structure has maximum depth which yields slight increase in latency. Slansky reduces the delay at the expense of increased fanout. Kogge-Stone achieves high speed and low fanout but produces complex circuitry with more numbers of wiring tracks . The Knowles trees are family of network between betweenKogge-Stone and Sklansky with increased fanout. Ladner Fischer introduced a network between Sklansky and Brent-Kung which provides a tradeoff between logic levels and fanout. T. Han and D.A. Carlson presented a hybrid construction of a parallelprefix adder using two designs the Kogge-Stone construction having the best feature of higher speed and the Brent-kung construction with best feature of low area requirement. A modified Han-Carlson adder uses fewer number of prefix operations by adjusting the number of stages amongst Kogge-Stone and Brent- kung adder and thus reduces the area required by the adder circuitry.
Fig. 2 shows HRPX Structure. The regular parallelprefix adder is used to do the first part of addition and the simplified RCA logic is used to do the second part where the corresponding bits of the operand are fully variable. Full adder can be designed with XOR/OR gates because of the constant operand. In this reverse converter design the carry chain is not needed and can be ignored. For most modulo sets (2ⁿ-1) addition is a necessary operation. The End around Carry (EAC) for (2ⁿ-1) addition is represented with two zero, but for the reverse converter design one zero representation is required. To correct these zero representation problem, a detector circuit was employed in the design but it incorporates additional delay. So, the Binary to excess one converter (BEC) is used to solve the double zero representation issue.
Abstract— Parallelprefix adder is used for speeding up the system’s logical operation. Execution of parallelprefix adder’s structure in VLSI has efficient performance. Parallelprefix adder structures are of different types i.e., Brent- Kung, Han-Carlson Adderetc. Have been projected earlier. Kogge- Stone adder with pipelining is the fastest adder structure among all of them. Kogge- Stone adder is the sub-type of parallelprefix adder in which it uses smaller amount of prefixing operation with black cells as compared with the other adder and final sum is calculated through post processing technique. In this paper, initially pipelining Kogge Stone adder is implemented and that result gives decrease in critical path delay and increase in speed.
ABSTRACT— A parallel-prefix adder gives the best performance in VLSI design. However, performance of existed adder through black cell takes huge memory. So, gray cell can be replaced instead of black cell which gives the Efficiency in proposed Adder. The proposed system consists of three stages of operations they are pre- processing stage, carry generation stage, post- processing stage. The pre-processing stage focuses on propagate and generate, carry generation stage focuses on carry generation and post-processing stage focuses on final result. In ripple carry adder each bit of addition operation is waited for the previous bit addition operation. In efficient proposed adder, addition operation does not wait for previous bit addition operation and modification is done at gate level to improve the speed and to decreases the memory used.
 David h,k hoe, Chris Martinez and srijyothsnavundavalli “Design and characterization of parallelprefix adders using FPGAs“, Pages.168-172, march2011 IEEE.  K.Vitoroulis and A.J. Al-Khalili, “performance of parallelprefix adders implemented with FPGA technology,” IEEE Northeast Workshop on circuits and systems, pp.498-501, Aug. 2007.
depends upon the initial inputs. Parallel: involves the execution of an operation in parallel. This is done by segmentation into smaller pieces that are computed in parallel. 7 Operation: any arbitrary operator that is associative is parallelizable. It is very fast because the processing is accomplished in a parallel fashion. In brief, the use of modular and regular parallel-prefix adders proposed in this brief in reverse converters highly decrease the delay at the expense of significantly more power and circuit area, whereas the proposed prefix-based adder components allows one to achieve suitable tradeoffs between speed and cost by choosing the right adders for the parts of the circuits that can benefit from them the most.
In this paper, we presented a scalable low power comparator with speed using regular digital structures consisting of two modules: the comparison module and the decision module. These modules are structured as parallelprefix trees with repeated cells in the form of simple gates that are one gate level deep with maximum fan-in and fan-out of four and five respectively, independent of input bitwidth.
It is shown that the results obtained for ParallelPrefix Adders are better than the serial adders in terms of delay and at the same time there is a trade-off with the area occupied. The results obtained for carry chain adders at higher bit widths (128 to 256 bits) has higher performance when compared to serial adders. Because the adder is often the critical element which determines to a large part the cycle time and power dissipation for many digital signal processing and cryptographically implementations,it would be worthwhile for future FPGA designs to include an optimized carry path to enable tree based adder designs to be optimized for place and routing. Inclusion of a ROM is being done in few adder designs to find the worst case delay combination of the input. Architectures that include fast carry chains and the possible tradeoffs are investigated. In the future, designs for Spanning Tree Adder(STA) and Sparse Kogge Stone Adder (SKA) are done and delay and area occupied are calculated to check performance enhancement keeping serial adders as reference.
Abstract: The focus of this paper is the actual implementation of parallelprefix adders and verifies the functionality of the adder for arithmetic and logical operations used in processors and for D.S.P applications. The parallelprefix adders we mainly have are Parallelprefix adders (PPA) have the better delay performance. This paper investigates four types of PPA’s (Kogge Stone Adder (KSA), Spanning Tree Adder (STA), BrentKung Adder (BKA) and Sparse Kogge Stone Adder (SKA)).Of all these adders we mainly focus on hybrid parallelprefix based components block instead of full adder circuits reversible gates are used such that high power consumption problems can be reduced.
In Fig.4 (a) the block diagram of a general self correcting CLA based PPA  is shown. It consists of input shift logic, pre-computation block, CLA prefix structure, post computation block and output shift logic. The CLA prefix structure includes duplicated important nodes (computation cells) and multiplexers to select the fault free node. This is the protected part of the prefix structure meaning a fault in this part can be masked and a fault free output is obtained. The other nodes which are not duplicated form the unprotected part of the prefix structure meaning a fault in this part may result in erroneous results. In case a fault is detected in the protected part the computation is done in multiple clock cycles. In the first cycle, one set of operands are applied and outputs are computed while in subsequent cycles the other outputs are calculated by shifting the inputs and using the fault free part of the PPA. To achieve this additional column(s) (for computation of shifted bits) are added. Depending on the architecture one or two additional columns are added. This has its fair share of drawbacks such as delay overhead (as computation in the faulty adder may require two or three clock cycles) and vulnerability to faults in the unprotected part of the prefix structure. It is proposed in this work to overcome these weaknesses in CLA based prefix adders to the extent possible by means of a fault tolerant self-correcting structure using Ling parallelprefix adders.
The Design is developed using Verilog and Synthesized using Xilinx 14.7 ISE. As a previous work different MAC Units were developed using different combination of multipliers and adders. Here in this implementation we selected modified Wallace multiplier with carry save adder to compare with our efficient method that is precision multiplier using parallelprefix adder and measure the performance parameters of MAC unit. The parameters are area, delay where area is measured in terms of number of slice and delay is measured in nanoseconds respectively.
BrentKung adder is used for high presentation addition operation. The Brent- kung is the adder of parallelprefix used to perform the operation of addition . It is looking like tree structure to perform the arithmetic operation. The Brent-kung adder consists of grey cells and black cells.  Each black cell consists of one OR gate and two AND gates . Each gray cell consists of only one AND gate.p i denotes propagate
Abstract: A variable latency adder pays speculations in arithmetic circuits can replaced with appropriate one, which will produces faster and correct results. In this paper it is proposed Variable-Latency Adder(VLA) based Brent-Kung Parallel-Prefix configuration that outperforms Kogge-Stone. In proposed adder has two stages of operations, one is Pre-processing stage and another one is Generation-stage. The pre-processing stage is the design has propagation and generation circuits. Generation stage producess on the carry generation and result and the performance of the Brent-Kung adder throughout black-cell attain the wide area. Gray cell can be replacing the place of black cell which provide the Efficiency in BKA. Finally, a new move towards the design of efficient 32 bit low-power variable latency parallelprefix Brent Kung Adder (BKA) concentrates the gate levels for improve increase & decreases memory. The Adder which gives the addition process offers great advantages in dropping delay. Brent-Kung adder mostly used for low- power Designs and in this paper implementation of Brent-Kung Adder synthesized using Xilinx ISE 14.7 has been modelled with VHDL.
The main objective of this project is to design the Reconfigurable n-bit LFSR By using the standard LFSR, modular LFSR ,complete LFSR and hybrid LFSR’s are made to be programmable. This can reduce the number of shifting process and increases the speed. By using the design of the Reconfigurable LFSR the ParallelPrefix Adder is testing. The ParallelPrefix Adder will reduce the power consumption rather than the other adders. The main criteria of this project is to increase the speed, reduce the power consumption and also delay.
In the event that it is quite recently critical to accomplish the minimum power utilization and equipment cost without considering speed, no prefix viper is required. Then again, if fast is the originator objective, the CPAs with EAC and the standard CPAs ought to be supplanted by conventional parallelprefix modulo 2n – 1 adders and customary parallel- prefix adders, separately. Be that as it may, for the VLSI creators, a reasonable tradeoff between speed, power, and range is frequently more critical. For this situation, to start with, CPAs with the EAC can be supplanted by the HMPEs. At that point, if the converter contains a standard CPA where one of its operands has a string of steady bits with the estimation of one, it can be supplanted with the HRPX.
stage conniving thatsome important ways ar started. instead, once P8:1 is zero, CO,p is adequate the G8:1. to boot, no important path are activated during this case. once the parallelprefix network, the intermediate car- ries, that ar functions of CO,p−1 and intermediate signals, ar computed (Fig. 7). Finally, within thepostprocess- ing level, the out-put sums of this stage ar calculable. It ought to be noted that this implementation relieson the similar schemes of the concatenation and incrementation ideas employed in the CI-CSKA explained. It ought tobe noted that the top a part of the SPL1 path from CO,p−1 to final summation results of the PPA block and also thebeginning a part of the SPL2 ways from inputs of this block to CO,p belong to the PPA block (Fig. 3). to boot, the same as the projected CI-CSKA structure, initial|the primary} purpose of SPL1 is that the first in- put little bit of the primary stage, and also the last purpose of SPL2 is that the last little bit of the add output of the incrementation block of the stage alphabetic character.
Objectives: This paper examines three variations of carry-tree adders (spanning tree adder, sparse Kogge-Stone & Kogge-Stone adder) and presents a comparison with Carry Skip Adder (CSA) & simple Ripple Carry Adder (RCA). Methods/Statistical Analysis: In VLSI designs the best performance can be obtained from Parallel-prefix adders (PPA) which are also termed as carry tree adders. Due to constraints on routing overhead & logic block configurations the advantage in performance in FPGA executions doesn't translate directly. Xilinx Spartan 3E FPGA is used to implement these designs which has varied bit-widths & the -performance logic analyzer is used for delay dimensions. Findings: Better delay performance is observed by the RCA designs of 128 bits due to the use of fast carry-chain. As in the case of carry-tree adders having bit widths of 256 bits there is a speed advantage over the RCA. RCA is the most commonly used adder implemented using full and half adders. As RCA is a serial adder which can perform any no. of additions but due to carry propagation there is a problem of propagation delay from stage to stage. PPAs are used to overcome delay problem as the carry is pre-computed. Various PPAs are Spanning tree, SKS adder, KS adder and Brent kung adders. Improvements: By using delay and power controls, design and comparison between these adders performed. Xilinx ISE software is used for synthesis process & simulation of these adders and results are presented in this paper.
In this system we use nuclear stages. In nuclear stages we have pre processing, parallelprefix network and post processing. One parallelprefix network is connected to other parallelprefix network through a skip logic. By using this proposed Hybrid Variable Latency the operation of the circuit is very fast.
Where “-1” is that the position of carry-input. The generate/propagate signals is classified in numerous fashion to induce constant correct carries. based on different ways of grouping the generate/propagate signals, completely different prefix architectures is created. Figure three shows the definitions of cells that are utilized in prefix structures, as well as bc and gc. For analysis of assorted parallelprefix structures, see ,  & .
The binary adder is the critical element in most digital circuit designs including digital signal processors (DSP) and microprocessor data path units. As such, extensive research continues to be focused on improving the power delay performance of the adder. In VLSI implementations, parallel-prefix adders are known to have the best performance. Parallelprefix adder is the most flexible and widely used for binary addition. ParallelPrefix adders are best suited for VLSI implementation. Numbers of parallelprefix adder structures have been proposed over the past years intended to optimize area, fan-out, and logic depth and inter connect count. This paper presents a new approach to redesign the basic operators used in parallelprefix architectures. The number of multiplexers contained in each Slice of an FPGA is considered here for the redesign of the basic operators used in parallelprefix tree.