POWER EVALUATION OF ADIABATIC LOGIC CIRCUITS IN 45NM TECHNOLOGY

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1 INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14) ISSN (Print) ISSN (Online) Volume 5, Issue 12, December (2014), pp IAEME: Journal Impact Factor (2014): (Calculated by GISI) IJECET I A E M E POWER EVALUATION OF ADIABATIC LOGIC CIRCUITS IN 45NM TECHNOLOGY Simranjeet Singh Puaar 1, Sandeep Singh Gill 2 1, 2 (ECE, Guru Nanak Dev Engineering College, Ludhiana, India) ABSTRACT Adiabatic logic technique can become an answer to the problem of power dissipation. This technique is capable of recycling the energy from the load and sends it back to the power supply. In this paper various adiabatic logic techniques like Efficient Charge Recovery Logic (ECRL), Positive Feedback Adiabatic Logic (PFAL), 2N-2N2P are analyzed. Combinational circuits like Nand, Nor, Exor, 2:1Mux are implemented using above mentioned techniques. Effect of frequency on energy consumption is analyzed and compared with the results of standard CMOS. saving factor (ESF) of all above said adiabatic techniques is determined at 1 MHz. After analysis it was found out that PFAL is most efficient. Design and simulations is done using CADENCE VIRTUOSO tool, in 45nm technology node. Keywords: Cadence Virtuoso, ECRL, ESF, PFAL, 2N-2N2P. 1. INTRODUCTION CMOS device is fast moving towards pinnacle of miniaturization, thus causing the increase in sophistication of applications in embedded computing. Interest of the researchers has grown towards reducing energy dissipation as cost of power dissipation has become derisory. Results obtained using custom low power techniques are sometimes inadequate hence different concepts of physics are being explored to optimize the power equation. Adiabatic logic technique is one such concept. In this paper various combinational circuits are implemented using semi adiabatic ECRL[1], PFAL[2][3], 2N-2N2P[3] techniques and comparison is made with traditional CMOS. 2. ADIABATIC PROCESS Adiabatic literally is a thermodynamic process which involves no energy exchange with the surrounding thus no loss of energy due to dissipation but in microelectronics charge transfer between nodes of a circuit is considered as a process.basic rules for adiabatic circuits: 1. Never turn on a transistor if it has a non zero voltage across it because it will cause ½ CV DD 2 dissipation. 2. Never suddenly change voltage across any On transistor [4]. Where C is a load capacitance and V DD is maximum amplitude of applied voltage. To satisfy above rules adiabatic switching is used. Adiabatic switching is technique which causes the nodes to charge/discharge at constant current to minimize energy dissipation.adiabatic Switching requires Constant current source power supply [5]. For adiabatic switching trapezoidal power supply voltage is used. 230

2 2.1 Power clock Trapezoidal voltage is used as a power clock which acts as a constant current source power supply. Power clock has four intervals, these are Evaluate(E), Hold(H), Recovery(R), Wait(W). In E interval, the outputs are evaluated from the stable input signal. During H interval, output is kept stable to provide input to next stage. is recovered during R interval and W interval is added for the purpose of symmetry as shown in the fig. 1. Fig.1: One cycle of power clock used in adiabatic logic 2.2 Lossmechanism in adiabatic logic Adiabatic logic energy loss (E AL ), Leakage loss (E leak ) and Non-adiabatic loss (E non-adia ) are the losses that occur in adiabatic circuits as shown in Fig. 2 [6]. Fig. 2: Variation in energy of adiabatic logics with frequency [6] From the graph it can be seen that E AL increases with frequency, E leak is inversely proportional to frequency and E non-adia is independent of the frequency. Thus for adiabatic circuit consumption at low frequency high due to leakage.power. consumption decreases as frequency increases and is minimum at a particular frequency and it start increasing after wards basically due to E AL [6]. 2.3 saving factor It is measure for how much more energy is consumed in a static CMOS gate or system with respect to an Adiabatic Logic counterpart [6]. General definition for ESF is given by (1). ESF= (1) 3. CIRCUIT IMPLEMENTATION Nand, Nor, Exor and 2:1Mux are the combinational circuits that are implemented using semi adiabatic ECRL, PFAL, 2N-2N2P techniques. Implementation is done using cadence virtuoso 45nm technology node. Supply voltage applied to run the circuits is trapezoidal in nature which has maximum amplitude of 1.8V. Length of both the MOS 231

3 devices is kept at minimum value i.e. 45 nm. Width of NMOS is set to 120nm and that of PMOS is set to 240nm. Load capacitance value is set to 1pf considering the fact that as gate width is decreased parasitic capacitance increases. 3.1 ECRL This adiabatic logic family has same structure as cascode voltage switch logic. This structure has two cross coupled PMOS devices that are used to provide complementary out. The latch is driven by nmos network that could be viewed as a complementary switching block.combinational circuits implemented using ECRL are shown in Fig. 3. Fig. 3: ECRL Implementation of a) Nand gate b) Nor gate c) Exor gate d) 2:1 Mux 3.2 PFAL In case of PFAL, latch is a combination of two pmosfets and two nmosfets, and the functional tree is connected in parallel with the pmosfets.as functional tree is parallel withpmosfets it causes the reduction of equivalent resistance of the charging path of the capacitor. During the recovery phase,the loaded capacitance gives back energy to the power supply, thus reducing overall power consumption [7].Combinational circuits implemented using PFAL are shown infig

4 Fig. 4 PFAL Implementation of a) Nand gate b) Nor gate c) Exor gate d) 2:1 Mux 3.3 2N-2N2P This logic family is derived from ECRL to reduce coupling effect that was a drawback of ECRL.In case of 2N- 2N2P latch is a combination of two pmosfets and two nmosfets, and the functional tree is connected in parallel with the nmosfets. These cross coupled nmos's result's in non-floating output as shown in Fig

5 Fig. 5: 2N-2N2P Implementation of a) Nand gate b) Nor gate c) Exor gate d) 2:1 Mux 4. RESULTS AND DISCUSSIONS In this section effect of frequency on energy consumption is analyzed and compared with the results of standard CMOS. saving factor (ESF) of all above said adiabatic techniques is determined at 1 MHz's Moreover different techniques compared for area consumed. 234

6 4.1 Effect of frequency on energy consumption Amount of energy consumed by adiabatic circuit depends upon frequency of operation. Effect of frequency on various adiabatic combinational circuits is analyzed. Analysis is tabulated in Table 1 to Table 4 and shown graphically in Fig.6.Results shown below indicate that at low frequencies energy consumption increases for both CMOS and adiabatic techniques due to leakage current that flows in transistors. From above it is seen that energy consumption is minimum in ECRL and maximum in PFAL. As frequency of operation is increased energy consumption decreases and is minimum at about 10 KHz. For mid frequency ranges PFAL is most efficient technique and all are better than standard CMOS. As frequency of operation increases energy consumption stars increasing in all the three techniques. At higher frequencies at about 10MHz, behaviour of adiabatic families remain no longer adiabatic, thus energy consumption of adiabatic logic devices increases whereas for CMOS it is independent of frequency. Table 1: consumption of Nand at different frequencies Frequency CMOS ECRL PFAL 2N-2N2P 100 Hz KHz KHz KHz MHz MHz Table 2: consumption of Nor at different frequencies Frequency CMOS ECRL PFAL 2N-2N2P 100 Hz KHz KHz KHz MHz MHz Table 3: consumption of Exor at different frequencies Frequency CMOS (pj) ECRL PFAL 2N-2N2P 100 Hz KHz KHz KHz MHz MHz

7 Table 4: consumption of 2:1 mux at different frequencies Frequency CMOS ECRL PFAL 2N-2N2P 100 Hz KHz KHz KHz MHz MHz Fig.6: consumption comparison of a) Nand gate b) Nor gate c) Exor gate d) 2:1 Mux 4.2 Transistor count Main disadvantage of adiabatic technique is transistor count. No of transistors used, are greater than corresponding CMOS device.transistor used are maximum for PFAL and 2N-2N2P and minimum for traditional CMOS. Table 5 shows transistor count comparison. Table 5: Number of transistors used to form a circuit Circuit CMOS ECRL PFAL 2N-2N2P Nand Nor Exor :1Mux

8 4.3 saving factor Table 6 shows the ESF of various adiabatic families for different combinational circuits calculated at 1MHz. From table it can be seen that PFAL has best energy saving factor i.e. PFAL is most efficient. Table 6: saving factor Circuit ECRL PFAL 2N-2N2P Nand Nor Exor :1 Mux CONCLUSION It is concluded from above that energy consumption at lower frequencies is minimum in case of ECRL followed by CMOS, 2N2N2P and PFAL i.e. leakage losses are minimum in ECRL. As frequency of operation increases energy consumption starts decreasing. It is minimum at about 10 KHz. At 10KHz and above PFAL is most efficient adiabatic logic technique followed by 2N2N2P and ECRL. At 10MHz and above process remains no longer adiabatic as a result energy consumption of all three adiabatic techniques becomes greater than CMOS. Frequency of operation of adiabatic logic could be increased to few hundred of MHz if load capacitance is reduced. Area consumption of adiabatic logic is greater than standard CMOS which is its main disadvantage. Thus its applications are limited, for example a pace maker where energy saving is main target. REFERENCES [1] Y.Moon, and D. K.Jeong, An Efficient Charge Recovery Logic Circuit, IEEE Journal of Solid-State Circuits, 31(4), 1996, [2] A.Vetuli,S. D.Pascoli, and L. M. Reyneri, Positive Feedback in Adiabatic Logic, IEEE Electronics letters, 32(20), 1996, [3] E.Amirante,A. B. Stoffi, andj.fischer, "Variation of power dissipation in adiabatic logic gates", Institute for Technical Electronics, Technical University Munich. [4] A.Schlaffer and J. A. Nossek, Is there a connection between adiabatic switching and reversible computing?,institute for Network Theory and Circuit Design, Munich University of Technology. [5] W. C.Athas, L.Svensson,J. G. Koller,N.Tzartzanis, ande. Y. Chou, Low-Power Digital Systems Based on Adiabatic-Switching Principles, IEEE Transactions on Very Large Scale Integration (VLSI) Systems, 2(4), 1994, [6] P.Teichmann, Adiabatic Logic(Springer series in advanced Microelectronics, 34, 2012) [7] A. Blotti, S.Di Pascoli, and R.Saletti, "Simple Model for Positive Feedback Adiabatic Logic Power Consumption Estimation", IEEE Electronics letters, 36(2), 2000, [8] Praveer Saxena, Swati Dhamani, Dinesh Chandra and Sampath Kumar V, Modified Two Phase Drive Adiabatic Dynamic CMOS Logic, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 3, Issue 2, 2012, pp , ISSN Print: , ISSN Online: