Monte-Carlo analysis of a new 6-T full-adder cell for power and propagation delay optimizations in 180 nm process
Authors: Ramana Murthy G. , Senthilpari C. , Velrajkumar P. , Tien Sze Lim 
Published: March 2014

Purpose
– Demand and popularity of portable electronic devices are driving the designers to strive for higher speeds, long battery life and more reliable designs. Recently, an overwhelming interest has been seen in the problems of designing digital systems with low power at no performance penalty. Most of the very large-scale integration applications, such as digital signal processing, image processing, video processing and microprocessors, extensively use arithmetic operations. Binary addition is considered as the most crucial part of the arithmetic unit because all other arithmetic operations usually involve addition. Building low-power and high-performance adder cells are of great interest these days, and any modifications made to the full adder would affect the system as a whole. The full adder design has attracted many designer's attention in recent years, and its power reduction is one of the important apprehensions of the designers. This paper presents a 1-bit full adder by using as few as six transistors (6-Ts) per bit in its design. The paper aims to discuss these issues.

Design/methodology/approach
– The outcome of the proposed adder architectural design is based on micro-architectural specification. This is a textual description, and adder's schematic can accurately predict the performance, power, propagation delay and area of the design. It is designed with a combination of multiplexing control input (MCIT) and Boolean identities. The proposed design features lower operating voltage, higher computing speed and lower energy consumption due to the efficient operation of 6-T adder cell. The design adopts MCIT technique effectively to alleviate the threshold voltage loss problem commonly encountered in pass transistor logic design.

Findings
– The proposed adder circuit simulated results are used to verify the correctness and timing of each component. According to the design concepts, the simulated results are compared to the existing adders from the literature, and the significant improvements in the proposed adder are observed. Some of the drawbacks of the existing adder circuits from the literature are as follows: The Shannon theorem-based adder gives voltage swing restoration in sum circuit. Due to this problem, the Shannon circuit consumes high power and operates at low speed. The MUX-14T adder circuit is designed by using multiplexer concept which has a complex node in its design paradigm. The node drivability of input consumes high power to transmit the voltage level. The MCIT-7T adder circuit is designed by using MCIT technique, which consumes more power and leads to high power consumption in the circuit. The MUX-12T adder circuit is designed by MCIT technique. The carry circuit has buffering restoration unit, and its complement leads to high power dissipation and propagation delay.

Originality/value
– The new 6-T full adder circuit overcomes the drawbacks of the adders from the literature and successfully reduces area, power dissipation and propagation delay.