Design and Analysis of High-Performance Carry Skip Adder using Various Full Adders

Adders are considered as the critical block in multipliers and other digital circuits. By improving the performance of the adder block, the overall system performance can be improved. Through this paper a correlative analysis of several adders like Carry Save Adder (CSaA), Carry Select Adder (CSeA), Carry Skip Adder (CSA), Ripple Carry Adder (RCA), Carry Look ahead Adder (CLA) designed and analyzed using Verilog HDL code. The performance metrics consider for comparison are area and delay. From the analysis performed, Carry Skip Adder has been concluded to be the better-performing one. The efficient full adder structure at the transistor level is identified namely 6T, 10T, 26T, and 24T. The identified transistor-level full adders are implemented in different block structures of 16 bit Carry skip adders to meet the better performing one. Simulation results show 8block CSA using 6T full adder is 37% efficient in the matter of delay and 8block CSA using 10T full adder is 35% efficient in the matter of power.

I. Introduction

In arithmetic operations, addition and multiplication are the basic and that is extensively used in processing applications [1]. Other blocks like subtraction (complement addition), division (successive subtraction), etc. are relay on addition. Hence adder only determines the entire performance of the system. There are a plethora of adder families(architectures) with varying power consumption, delay, and area usage. Few of the examples for them are Carry Skip Adder (CSA), Ripple Carry Adder (RCA), Carry Select Adder (CSeA), Carry Save Adder (CSaA), and Carry Look ahead Adder (CLA) which can be used based on their properties to improve the system performance. Meanwhile, enhancing the 1 bit full adder in the root level will consequently result in the routine augmentation of the entire structure. The performance of the full adder also greatly depends on the style that is adopted. The factors like transistor logic, transistor count etc. The 1-bit adder is a deciding factor in the operation speed of a circuit and it can be found indirectly with the help of delay time calculation. Similarly, the transistor's switching activity and its count can help to determine the circuit's speed of operation.