A novel Majority Gate ByUsing AmbipolarCNTFETs
Amir Shadmanpour1andPeimanKeshavarzian2
1Department of Computer Engineering, Science and Research branch, Islamic Azad university, kerman, Iran.
2Department of Computer Engineering, Islamic Azad university of Kerman, Iran
ABSTRACT
In this paper, presented a new majority gate by using ambipolarcntfet transistors. To design this majority gate, which include new AND-2 and OR-2 gates used the minimum number of transistors. Also for design new AND-2 and OR-2 gates, we have benefited from ambipolar transistors. As regards, ambipolar transistors have double-gate property and the most important feacher of these transistors are transmission gate, also, the proposed gate include smallest number of transistors, expected our gate designed to be the fastest and smallest gate.
KEY WORDS :Majority gate, Ambipolarcntfets, New AND-2/OR-2, Carbon nano-tube, Ambipolar majority gate, quick majority
1. INTRODUCTION
One of the new devices are cntfets that the transistors are scaled, by this feature expected to increase circuit performance. One of the main differences between cntfets and mosfets are channel components that carbon nano-tubes instead of silicon is used. Other differences between these two type of transistors are greater current carrying one-dimensional gate control of carbon nanotube to silicon[1,2]. Although the two types of transistors is similar, but cntfets due to the different gate cause optimize the threshold voltage and also using contact metal drain/source cause reduced shotkky barrier[3]. Because, the oxygen plasma is used in cnts, most chances in front of silicones to selection[4]. The reason for reliable carbon nanotubes is an electric field in the process of manufacturing and processing of cnts. Simulation results show that energy delay in carbon nanotubes almost 13 × better than mosfets [1,2,5]. Many researchers prefer using CNTFETs in the design of logic gates and memory [6]. Researchers by using of carbon nanotubes and enjoying the shottky barrier idea, new ideas found in transistors which called ambiplolarcntfet.
In this study, in part II shows a brief description of the structure and function of ambipolar transistors. And also, in port III, we will discussed to full description of the proposed majority gate and the full expression of our ideas. Finally, in section IV, we will conclude.
2. AMBIPOLAR CNTFETs
Researchers by using shottky barrier ideas found new innovations in science transistors. Ability to control the polarity of n-type and p-type transistors in CNTFET technology by control of the border gate, new ideas for the use of the second gate brovided. Polarity gate electrically, field at the cnt/metal junction and where the polarity is set to control [7,8].
Control gate is an electric field which located within the cnt and it’s task is to distinguish between the two gates. Whereas, polarity gate is an electric field that located within the framework cnt to drain and cnt tosource. In figure 1, a view of ambipolarcntfets transistor is shown.
figure 1. View of ambipolar double-gate CNTFET
The researchers used a substrate that has a function as a back gates as PG and this result is in control of all PGs. Lately, a self-aligned drain/source in [9] suggested. The aim of this ideas, study of unipolarcntfets. This technique orderly queuing used for making regular queuing PGs and CGs in design very compact device and enabling high gate[10,11]. Figure 2 shows an cross-section device. The main idea of this device is an follows : carbon nano-tube are deposited on the oxidized layer and covered by a layer of oxid nuclear(ALD), then an aluminum gate control in the middle of cnt is used. The negative AL2O3 guarantees insulation from the control gate to gate polarity. Then polarity gate terminals are activated and drain and source are connected[11,13].
Figure 2.Ambipolar CNFET: device (a), layout (b), symbol (c)
Another method of manufacture, the compact circuit layout used of double-gate shottky barrier cntfets(figure 3.a)[14]. It’s terminals includes drain, source, PG and CG. By using of si substrate that included some cntfet models by which can change the behavior of the device. In figure 3.b you can see the symbol is used and figure 3.c shows how to choose n and p-type devices which dependent on the voltage applied to the PG terminal. Ambipolarcntfets, provides the opportunity to have field programmable transistor[15].
Figure 3. Double gate ambipolar transistor. (a) Layout. (b) Symbol. (c) Configuration as n-type and p-type.
3. PROPOSED DESIGN
Majority function is one of functions which in design of full adder circuit is used [17]. In the paper [17,18,19 ] observed that the capacitors are used to build the majority function. Use capacitors is one of the factors that lead to high power consumption of this circuit. The performance majority is considers the maximum inputs. According to table 1, the output will be “1” when at least two of the three inputs entriehave a value of “1”. And also if at least two of the three inputes have a value of “0”, the output will be value of “0”.
Table 1. Truth table of majority gate
a / b / c / Output0 / 0 / 0 / 0
0 / 0 / 1 / 0
0 / 1 / 0 / 0
0 / 1 / 1 / 1
1 / 0 / 0 / 0
1 / 0 / 1 / 1
1 / 1 / 0 / 1
1 / 1 / 1 / 1
We used the truth table for the design of majority gate. So that, the truth table can be divided into two parts.With this approach, we can design the circuit with minimum transistor.In this case, we selected “a” input as condition of truth table. And also, with the simple clause at a time half circuit will be cut-off and the other half of the circuit is only active. So, if a = 0 the output will be “AND” gate and if a=1 the output will be “OR” gates. In addition, we are enjoying ambipolar transistors designed this gate. As regards, by ambipolar transistors just designed XOR and XNOR gates, we use interesting and new ideas overcome designing AND and OR gates and we use them in our majority gate. For design “AND-2” gate, we used the XNOR ambipolarcntfets.
b / c / XNOR / AND0 / 0 / 1 / 0
0 / 1 / 0 / 0
1 / 0 / 0 / 0
1 / 1 / 1 / 1
Table 2. Truth table of XNOR and AND gates
According to XNOR gate law, when the two inputs are not same, the output will be “0” and when the two inputs are same, the output will be “1”. As you can see in table 2, to convert the XNOR table to And table should look for similarities and difference between these two tables. When ( bc = 01 and bc = 10 ) both tables have zero output. So, no need to change these two outputs in AND table. In this made, the output always will be zero. By connected input b or c to source terminal, we succeeded in time (“0” and “1”) the output circuit to zero and one values changed, respectivle. So, we used this approach interesting and could designing AND-2 gate only one ambipolar transistor. Figure 4.a shows the proposed ambipolarcntfet AND gate.
Table 3. Truth table of XOR and OR gates
0 / 0 / 0 / 0 / 0
0 / 1 / 1 / 0 / 1
1 / 0 / 1 / 0 / 1
1 / 1 / 0 / 1 / 1
(a) (b) (c)
For design OR gate based ambipolar, we’ve benefited from the XOR and AND gates. Act XOR gate, when the inputs have equal amounts (bc = 00 and bc = 11) the output will be zero. Also, when the input values are not equal (bc = 01 and bc = 10), the output will be “1” (according to table 3.a ). Also, according to And gate law, the output value will be “1” when both input values are equal to 1, in order word, both inputs connected (bc = 11,table3.b). On the other, act OR gate, when at least one of the inputs have value “1” (connected), the output will be “1” (according to table 3.c). We’ve combined AND gate and XOR gate and with this combination, we design OR gate by ambipolar transistors. Figure 4.b shows the proposed ambipolarcntfet OR gate.
Figure 4. The proposed AND-2/OR-2 gates : AND-2(a), OR-2 (b)
After making the AND-2 and OR-2 gates, we need to design a majority gate. We combine these two gates designed a majority gate. In fact, if a = 0, the output should be connected to the “AND” gate and if a = 1, OR gate results goes to output. The proposed majority gate is shown in figure 5.
Figure 5. The proposed majority gate
Among of the very good features of majority gate : First, the use of ambipolar transistors that benefit from the property transmission gate, secondly, by activating half of the circuit in one time and disable the other half will increase the circuit speed. Also, in this circuit is used to minimum number of transistors to construct.
4. CONCLUSION
In this study, we designed a majority gate by using AND-2 and OR-2 gates and benefited of ambipolarcntfet transistors. The design of this gate, circuit divided two parts. In fact, a partition of the circuit always is off and other part is active. This is one of the most important ideas that are very effective in reducing the number of transistors and circuit speed. According to the main characteristic of ambipolar transistors is that acts like a transmission gates. So, the output should best rate and values 0 and 1 would be ideal.
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