Analysis of Various DCVSL Structures and Implementation of Full Adder with Them

Abstract

The Differential Cascode Voltage Switch Logic (DCVSL) is a CMOS circuit technique which has potential advantages over conventional NAND/NOR logic in terms of power dissipation, circuit delay, layout density and logic flexibility. In this paper, a detailed comparison of all the DCVSL structures are provided including the implementation of Full Adder circuit with the help of those DCVSL structures, which includes Static DCVSL, Dynamic DCVSL and Modified DCVSL. The performance analysis is done in Cadence Virtuoso 90nm CMOS Technology. The working of these DCVSL structures is based on the concept of ‘Multiplexer’. A multiplexer also known as ‘mux’, which is a device where from a number of input signals, selection is done. It is basically a combinational logic circuit. The multiplexer is a unidirectional device, which is used in applications where a data must be switched from multiple sources to a destination. The analysis of all these DCVSL structures is followed by the implementation of Full Adder. Adders are the building blocks in computer systems. Digital Computer Systems widely uses Arithmetic operations. Addition is a necessary arithmetic operation, which is also the root for arithmetic operation such as multiplication. Similarly, adding another XOR gate, the basic adder cell can be modified to function as subtractor, which can be used for division. Therefore, 1-bit Full Adder cell is the ultimate and simple block of an arithmetic unit of a system. So, the basic 1-bit Full Adder cell must be improved, so that the performance of the digital circuits. In VLSI, there is always a trade-off between speed and power dissipation. One parameter is improved, the other gets degraded. Hence, the parameter power delay product is introduced. So, to achieve speeds, high drivability hybrid-DCVSL design methodologies are used to build adder cell in this work. The DCVSL gates produces both complementary and true outputs using single gate architecture. And, the multipliers in the design are based on the pass transistor logic (PTL), because these occupies less chip area per component and also are simple to construct. The parameters compared are power dissipation, propagation delay time, power delay product, transistor number and power dissipation (average). The Static DCVSL structure produces best result in terms of power dissipation, delay and power delay product. Whereas, in case of the Adder circuit, the power consumption is best for the Dynamic DCVSL Adder, along with the delay and the power delay product for the output Sum; but for the output Cout, the best option is Static DCVSL Adder, as the delay and the power delay product is least in this case.