Efficient implementation of full adder for power analysis in cmos technology

Efficient implementation of full adder for power analysis in cmos technology

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  Kaleeswari .S, Saranya.K, Muniraj N. J. R, International Journal of Advance Research, Ideas and Innovations in Technology. © 2017, www.IJARIIT.com All Rights Reserved Page | 115 ISSN: 2454-132X Impact factor: 4.295 (Volume3, Issue6) Available online at www.ijariit.com Efficient Implementation of Full Adder for Power Analysis in CMOS Technology S. Kaleeswari Assistant Professor, Department of ECE, Tejaa Shakthi Institute of Technology for Women, Coimbatore, Tamil Nadu saranyaautomatic@gmail.com K. Saranya PG Scholar Department of ECE, Tejaa Shakthi Institute of Technology for Women, Coimbatore, Tamil Nadu skaviya18@gmail.com Dr. N. J. R Muniraj Principal Department of ECE, Tejaa Shakthi Institute of Technology for Women, Coimbatore, Tamil Nadu njrmuniraj@yahoo.co.in Abstract: In recent days, the real-time application and fast arithmetic operations require highly efficient arithmetic hardware architecture to improve the system performances. The adder plays a vital role in digital circuits, the earlier hardware architecture using conventional CMOS and transmission logic gate based full adder design. Moreover, the techniques using more number of transistors and consume larger power and delay so we proposed the techniques pass-transistor logic and transmission gate based hybrid pass logic. The hybrid technique is used to reduce the number of the transistor, so the delay and power consumption will be reduced when compared with the earlier techniques. The proposed technique design was implemented using 16 transistors in 180nm CMOS technology and it consumes 8.2075nW power and the delay reduced to 5.0146ns. Keyword: CMOS. Transmission gate, Pass-Transistor Logic, Adder. I. INTRODUCTION A full adder is one of the most fundamental building blocks of all the circuit application. Standard static CMOS, dynamic CMOS logic, complementary pass transistor logic (CPL) and transmission gate full adder are the most logic styles in the conventional domain [1]. In general, one bit full adder core has three inputs (A, B and carry in Ci) and two outputs (sum S and carry out Co).The adder performance may improve the power and speed with driving capability. The performance of full adder can significantly affect the system performance [2]. At the circuit level, the optimized design is used to avoid degradation in the output voltage, and it consumes less power and delay in the critical path [5]. Using the complementary pass transistor logic (CPL) the adder circuit will operate at low supply voltage with signal integrity [6]. From the gate logic design, the full adder can be implemented using exclusive-OR gates, since the sum can be expressed as an XOR function and output can be expressed as a multiplexer function [7]. The power dissipation characteristics are compared qualitatively and quantitatively with gate implementation. Lowering supply voltage also increases the circuit delay and degrades the drivability of the cells [8]. Clustered voltage scaling (CVS) and Dual voltage supply (dual-VS) have been proposed to maintain the chip throughput by selectively lowering the supply voltage.The critical path traverses from the carry-in to the carry-out of the full adders. To optimize and analyze the performance of different full adders, a tree-structured setup is proposed. Each of these modules is implemented, optimized and tested separately [6]. Several full-adder cells are composed by connecting these modules. Adders are an extensively used component in data paths and the design and analysis are required for these units to obtain optimum performance. To execute an arithmetic operation a circuit can consume very low power by clocking at low frequency to complete the operation.GDI techniques are used to reduce power consumption, propagation delay [9]-[14]. The major sources of power consumption in CMOS circuits are switching power, short circuit power and leakage power [15]. The performance and complexity at the transistor level directly influence the overall performance of the system. The gate-based Full adders with conventional methods result in a higher number of transistors and consequently more power consumption, delay, and area wastage [17] –[19]. Lowering the supply voltage appears to reduce power consumption. However, lowering supply voltage also increases circuit delay and degrades the drivability of cells designed with certain logic styles [20]-[23]. The power-delay product (PDP) represents a tradeoff to be optimized between two conflicting criteria of power dissipation and circuit latency. In VLSI the adders are basic components for an ALU. There is N number of adders their own advantage and disadvantages.
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  Kaleeswari .S, Saranya.K, Muniraj N. J. R, International Journal of Advance Research, Ideas and Innovations in Technology. © 2017, www.IJARIIT.com All Rights Reserved Page | 116 When two numbers are to be added and if each of them is of N bits than we can add in two ways they are serial and parallel. In serial addition, the LSBs are added first then the carry created are propagated to the next higher bits. In parallel addition, it added in parallel without waiting for carrying and different algorithms are used to compensate for the carry. In CMOS the adders are classified based on the propagation of carry between the stages they are Ripple Carry Adder (RCA), Carry Skip Adder (CSKA), Carry Increment Adder (CIA), Carry Look Ahead Adder (CLA), Carry Save Adder (CSA), Carry Select Adder (CSLA) and Carry Bypass Adder (CBA). RCA contains the series structure of Full Adders each full adder is used to add two bits along with carrying bit. The carry generated from each full adder is given to next full adder and the delay is more as the number of bits is increased. CSA uses skip logic in the propagation of carrying. It is used to speed up the operation by adding a propagation of carrying bit around a portion of the entire adder. Carry increment adder (CIA) consists of ripple carry adder and incremental circuitry. The addition operation is done by dividing a total number of bits into a group of 4- bits and addition operation is done using several 4-bit ripples carry adder. Carry look Ahead (CLA) is based on the principle of looking at lower adder bits of argument and added if higher orders carry generated. This adder reduces the carry delay by reducing the number of gates through which a carry signal propagates. Carry save adder (CSA) three bits are added parallel, in this carry is not propagated to the stages. The delay due to the carrier is reduced. Carry select adder (CSLA) architecture consists of the independent generation of sum and carry i.e., cin=1 and cout=0 are executed parallel. Carry Bypass adder (CBA), ripple carry adder is used to add 4-bits at a time and the carry generated will be propagated to next stage. II. PROPOSED SYSTEM The simulation of the proposed full adder was carried out using 180 nm technologies and compared with the other adder techniques like conventional CMOS (C-CMOS), Transmission gate adder (TGA), Transmission full adder (TFA) and 10T transistor design. The proposed techniques consist of pass transistor logic and transmission gate based hybrid pass logic. The pass transistor logic is driven by periodic signal and it reduces the count of transistors used to make different logic gates, by eliminating redundant transistors. Transistors are used as switches to pass logic levels between nodes of a circuit, instead of as switches connected directly to supply voltages and this reduces the number of active devices. The power consumption is minimized mainly by sizing the transistors in inverter circuits while the carry propagation delay will be improved by sizing the transistor between the paths from cin to court. The power consumption may be classified into static and dynamic power. The static power is mainly due to biasing, leakage currents and sub-threshold conduction. To minimize the static power the inverters should have a large channel width. The difference in static and dynamic power consumption is large because of increases in subthreshold conduction current and the leakage. The proposed hybrid adder requires only 16 transistors whereas the other hybrid technique requires more than 16 transistors. The average power consumed by the proposed full adder is significantly lower than that of the other hybrid full adders. Figure 2 shows the detail diagram of the proposed full adder. The sum output of the full adder is implemented XNOR modules. The inverter comprised of pmos and nmos transistors which generate the input B. Output of the controlled inverter is basically the XNOR of A and B. The performances analysis of proposed full adder was performed with 1.8v supply voltage with 180nm technology. The uses of less number of transistors in proposed full adder also improve the speed. The table1 represents a detailed comparison of the proposed full adder with other hybrid full adders in 180nm technology which is discussed below. Table1: Simulation result for full adders in 180 nm technology Design Avg. Power(nw) Delay (ns) Transistor count C-CMOS 22.473 28.14 28 TGA 8.3741 5.0595 20 TFA 24.504 9.7605 16 10T 24.44 4.75496 10 Proposed 8.2075 5.0146 16
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  Kaleeswari .S, Saranya.K, Muniraj N. J. R, International Journal of Advance Research, Ideas and Innovations in Technology. © 2017, www.IJARIIT.com All Rights Reserved Page | 117 Figure1: Circuit for proposed full adder III. SIMULATION AND RESULT The analysis which includes different circuits like C-CMOS, TGA, TFA, 10T and proposed adder has been based on simulation runs on cadence using 180nm technology. By optimizing the number of the transistor of a full adder, it is possible to reduce the delay of all adders without increasing the power consumption. Buffers are attached to TFA, TGA and 10T circuits to enhance driving capability. Figure 2 represents the output of proposed full adder circuit in which the delay and power will be calculated. Figure 2: Output of proposed full adder Figure 3. Comparison of delay and power The performance of the proposed full adder in terms of average power and delay with supply voltage and comparison with other existing design is shown in above figure 3.
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  Kaleeswari .S, Saranya.K, Muniraj N. J. R, International Journal of Advance Research, Ideas and Innovations in Technology. © 2017, www.IJARIIT.com All Rights Reserved Page | 118 CONCLUSION In this paper, we proposed a low power hybrid 1-bit full adder in CMOS design. The simulation was carried out using cadence virtuoso tool 180 nm technologies and compared with other designs like C-CMOS, TFA, TGA, and 10T. The simulation result offered that the established proposed adder reduces the power compared with earlier designs. The hybrid technique is used to reduce the no of the transistor, so the delay and power consumption will be reduced when compared with the earlier techniques. The proposed technique design was implemented using 16 transistors in 180nm CMOS technology and it consumes 8.2075nW power and the delay reduced to 5.0146ns. REFERENCES [1] C.K.Tung, Y. C. Hung, S. H. Shieh and G. S. Huang, (2007), ‘‘A low-power high-speed hybrid CMOS full adder for embedded system’’, in proc. IEEE conf. Design diagnosis electron circuits syst., vol.13, pp.1-4. [2] S. Goel, A. Kumar and M. A. Bayoumi, (2006), ‘‘Design of robust, energy-efficient full adders for deep-sub micrometer design using hybrid-CMOS logic style’’, IEEE trans. very large scale integer. (VLSI) syst., vol.14, no.12, pp. 1309-1312. [3] D. Radhakrishnan, (2001), ‘‘Low-voltage low-power CMOS full adder’’, IEEE proc. circuit device syst., vol.148, n0.1, pp. 19-24. [4] R. Zimmermann and W. Fichtner, (1997) ‘‘Low-power logic styles: CMOS versus pass-transistor logic’’, IEEE J .Solid-state circuits, vol.32, no.7, pp. 1079-1997. [5] C. H. Chang, J.M.Gu and M. Zhang, (2005), ‘‘A review of 0.18 µm full adder performances for tree structured arithmetic circuits’’, IEEE trans. Very large scale integer. (VLSI) syst., vol. 13, no. 6, pp. 686-695. [6] A. M. Sharms, T. K. Darwish, and M. A. Bayoumi, (2002), ‘‘Performance analysis of low-power 1-bit CMOS full adder cells’’, IEEE trans. Very large scale integer. (VLSI) syst., vol.10, no.1, pp. 20-29. [7] M. Zhang, J. Gu and C. H. Chang, (2003), ‘‘A novel hybrid pass logic with static CMOS output drive full-adder cell’’, in proc. Int.symp.circuits syst., pp. 317-320. [8] S. Wariya, G. Singh, R. K. Nagaraj, and S. Tiwari, (2011)’ ‘‘Design analysis of XOR (4T) based low voltage CMOS full adder circuit’’, in proc.IEEE Nirma Univ. Int. conf.Eng. (NUiCONE), PP. 1-7. [9] S. Goel, M. Elgamel, and M. A. Bayoumi, (2003), ‘‘Novel design methodology for high-performance XOR-XNOR circuit design’’, in proc. 16th symp.integr.circuits system.design (SBCCI), pp. 71-76. [10] J.M.Wang, S.C.Fang and W.S.Feng, (1994), ‘‘New efficient designs for XOR and XNOR functions on the transistor level’’, IEEE.J. Solid-state Circuits, vol. 29, no.7, pp. 780-786. [11] M. J. Zavarei, M. R. Baghbanmanesh, E. Kargaran, H. Nabovati and A. Golmakani, (2011), ‘‘Design of new full adder using hybrid-CMOS logic style’’, in proc. 18th IEEE Int. conf. Electron.circuit system. (ICECS), PP. 451-454. [12] M.Alioto, G.Dicataldo and G.Palumbo, (2007), ‘‘Mixed full adder topologies for high-performance low-power arithmetic circuits’’, microelectronics. J., vol. 38, no. 1, pp. 130-139. [13] X. Wu and F.Prosser, (1998), ‘‘Design of ternary CMOS circuits based on transmission function theory’’, Int. J.Electron., vol. 65, no. 5, pp. 891-905. [14] K. Navi, M. H. Moaiyeri, R. F. Mizaee, O. Hashemipour and B. M. Nezhad, (2009), ‘‘Two new low-power full adders based on majority-not gates’’, microelectron.J, vol. 40, no. 1, pp. 126-130. [15] H.T. Bui, Y.Wang and Y.Jiang, (2002), ‘‘Design and analysis of low-power 10-transistor full adders using novel XOR- XNOR gates’’, IEEE Trans.circuits system.II Analog digit signal process., vol. 49, no. 1, pp. 25-30. [16] K. Navi, (2009), ‘‘A novel low-power full adder cell with a new technique in designing logical gates based on static CMOS inverter’’, microelectron.J, vol. 40, no. 10, pp. 1441-1448. [17] S. Kaleeswari is presently pursuing Master degree in VLSI Design at Tejaa Shakthi Institute of Technology, Coimbatore. She is interested in CMOS VLSI design using Cadence Virtuoso. [18] K. Saranya obtains BE ECE in Avinashilingam Deemed university and ME VLSI design in Anna university Coimbatore and she is presently working as a Assistant professor in Department of ECE at Tejaa Shakthi institute of Technology, Coimbatore and 6 years guiding students.