Research Article  Open Access
Varsha S. Bendre, A. K. Kureshi, Saurabh Waykole, "Design of Analog Signal Processing Applications Using Carbon Nanotube Field Effect TransistorBased LowPower Folded Cascode Operational Amplifier", Journal of Nanotechnology, vol. 2018, Article ID 2301421, 15 pages, 2018. https://doi.org/10.1155/2018/2301421
Design of Analog Signal Processing Applications Using Carbon Nanotube Field Effect TransistorBased LowPower Folded Cascode Operational Amplifier
Abstract
Carbon nanotube (CNT) is one of the embryonic technologies within recent inventions towards miniaturization of semiconductor devices and is gaining much attention due to very high throughput and very extensive series of applications in various analog/mixed signal applications of today’s highspeed era. The carbon nanotube field effect transistors (CNFETs) have been reconnoitred as the stimulating aspirant for the future generations of integrated circuit (IC) devices. CNFETs are being widely deliberated as probable replacement to silicon MOSFETs also. In this paper, different analog signal processing applications such as inverting amplifier, noninverting amplifier, summer, subtractor, differentiator, integrator, halfwave and fullwave rectifiers, clipper, clamper, inverting and noninverting comparators, peak detector, and zero crossing detector are implemented using lowpower folded cascode operational amplifier (opamp) implemented using CNFET. The proposed CNFETbased analog signal processing applications are instigated at 32 nm technology node. Simulation results show that the proposed applications are properly implemented using novel folded cascode operational amplifier (FCOA) implemented using CNFET.
1. Introduction
Over the last few decades, the electronics industries have seen remarkable growth in integrated circuits applications. There is substantial increase in integration density, speed, and performance, which results in highspeed portable devices and such demands are still raising in daytoday life. Power dissipation and heating constraints are also increasing with every new technology, as emerging silicon technologies continues to scale unfathomable into the ultrananometer regime. Through the last few decades, significant efforts are made to reduce the power budget ensuring high performance. But, the aggressive scaling of MOS transistors now approached to the fact that the channel and gate oxide becomes very thin and diffusion regions of transistors are in such vicinity that the charge carriers can easily cross the channel in vertical direction leading to unwanted currents through it and hence further horizontal scaling is not possible. As anticipated by the International Technology Roadmap for Semiconductors [1], rigorous exploration is desirable in order to endure this process and, undeniably, to encourage novel devices and methods that will move the technology developments in other directions [2, 3]. Carbon nanotube fieldeffect transistor (CNFET) is the competitor transistor which will permit for both the scaling process to sustain and for the progress of novel devices [4]. The details of CNFET and its properties are explained in Section 2.
Operational amplifiers (opamps) are indispensable blocks in almost all analog/mixed signal applications [5]. Design and development of maximum throughput analog integrated circuits is fetching progressive constraining due to the persistent tendency towards scaling in very deep submicron regime. There is a significant degradation in the performance of opamp in nanometer regime and there is a stringent requirement to reconnoitre new circuit design strategies for new upcoming devices like CNFET for their speedy merchandise to prolong Moore's law in deep nanometer regime [6]. Explanation of finest design of CMOSbased folded cascode opamp is extensively discussed by us in [7] and will not be covered here. Brief about CNFET and its performance comparison with CMOS is explained in section 2. Design of CNFETbased FCOA and the effect of pitch and diameter on the performance parameters are explained in Section 3. Section 4 explains different analog signal processing applications implemented using CNFETFCOA at 32 nm technology node. Concluding remarks towards the achievement of various performance metrics using CNFET are stated in Section 5.
2. Carbon Nanotube Field Effect Transistor
CNFETs are the transistors in which number of carbon nanotubes (CNTs) acts as a physical channel between source and drain unlike virtual channel in case of metal oxide semiconductor field effect transistor (MOSFET) [8]. CNTs are thin sheets of graphene. Graphene is an allotrope of carbon made up of tightly packed thin layer of pure carbon atoms. This thin singlelayered sheet is then rolled into tubes along different directions to form either metallic or semiconducting singlewalled CNTs (SWCNTs). This direction of rotation is termed as the chirality and represented in the form of sum of two vectors (n, m), as shown in Equation (1), representing two different directions. Out of these two types of SWCNTs, metallic nanotubes are widely used as interconnect and semiconducting nanotubes have captivated prevalent attention as an alternative solution for highperformance transistors in nanometer regime [9, 10]. An SWCNT is a conductor if n − m = 3k (k € Z); otherwise it is a semiconductor [11], where n, m are positive integers that specify the chirality of the tube [7–13]. The magnitude of the chirality depends on the diameter of the CNT and is determined by using Equation (2):where is the carbontocarbon atomic distance, which is ∼2.49 Å.
A distinctive construction of a CNFET device is demonstrated in Figure 1. All regions in this device are heavily doped except the CNT channel region, which is completely undoped. Analogous to the MOSFET, a CNFET also has a threshold voltage which needs to turn on the device. An inimitable feature of the CNFET device is the adjustability of its threshold voltage by changing the diameter of the CNTs. This is due to the fact that the CNT band gap, which is the function of the threshold voltage, depends inversely on the diameter as shown in the following equation [11, 14, 15]:where “” is the unit electron charge and (∼3.033 eV) is the carbon pp bond energy in the tight bonding model. This pertinent property makes the CNFET very useful for voltage mode analog and digital circuits [7, 11].
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2.1. Performance Comparison of CMOS and CNFET with Respect to Electrical Characteristics
CNFETs are better than bulk complementary metal oxide semiconductor (CMOS) transistors in case of contact resistance, subthreshold slope, and current drive capability. The contact resistance and the subthreshold slope of a CNFET are analogous to those of CMOS transistors. The CNFET current is measured in current per tube and can be increased by increasing the number of tubes, while a CMOS current drive is characteristically represented in current per unit device width (e.g., µA/µm) [12]. The ON current of CNFET can be approximately given by Equation (4) and it has little dependency on the channel length in case of nearballistic transportation:where is the length of the doped CNT source region, is the source resistance per unit length of doped CNT, and is the transconductance per CNT and is given by the following equation:where and are the carrier mobility in CNT and gate to channel capacitance per unit length, respectively.
IV characteristics of a typical 32 nm MOSFETlike NCNFET and PCNFET are shown in Figure 2(a). According to Figure 2(b), a 32 nm CNFET has proper I_{d}V_{ds} characteristics without short channel effects, whereas the 32 nm MOSFET suffers from higher channel resistance in the triode region, degraded r_{0}, and velocity saturation. Furthermore, as illustrated in Figure 2(b), besides the considerable higher ION/IOFF of the CNFET, it has a quadratic I_{d}V_{gs} curve in the saturation region while the MOSFET device has a linear I_{d}V_{gs} curve, mostly due to velocity saturation. Hence, it can be concluded that the MOSFETlike CNFET can be a promising device for designing some nanoscale analog circuits such as precise comparators and highgain amplifiers [11].
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Additionally, compared to bulk CMOS, the effective gate capacitance of one CNT per gate of CNFETs is about 4% and the current drive capability of each CNT is about 50% in contrast to bulk ntype MOSFET [12]. This is due to the ballistic transport of carriers along the CNT in specific direction. This results into 13 times better CV/I performance of CNFET over that of bulk ntype MOSFET. Enhancement in performance of pCNFET is more than that in nCNFET as compared to PMOS and NMOS, respectively. This is due to the similar behaviour and the current driving capability of a pCNFET compared to those of an nCNFET. The major problem associated with CNFET is the significant amount of leakage current in the off state, but it can be rectified by controlling the band to band tunneling and the full band gap of the CNTs which is less than for a MOSFET [13–17].
Moreover, the motion of the electrons in the nanotubes is sternly confined along the direction of tube axis, due to the quasi1D structure of CNT. Hence, only forward and backward scatterings are possible for the carriers in nanotubes, and all other scatterings are prohibited. The experimentally observed mean free path (MFP) is ∼1 µm [18, 19], which implies nearballistic carrier transport. Typical range of mobility is very high, up to 10^{3}∼10^{4} cm^{2}/V·s observed during conductance experiments in transistors and as has been proved by a diversity of studies [20, 21]. Hypothetical study too forecasts a mobility of ∼10^{4} cm^{2}/V·s for semiconducting CNTs [22]. The current carrying capability of multiwalled CNTs are confirmed to be more than 10^{9} A/cm^{2}, about 3 orders greater than the extreme current carrying capacity of copper and also able to sustain the same performance well above the room temperature [19]. In nutshell, the superior carrier transport and conduction characteristic makes CNFETs a promising candidate for nanoelectronics applications [13].
With these tremendous features of CNTs and CNFETs, circuit design using CNFET is on the top choices of circuit designers. However, more emphasis and hence extensive research is done in digital circuit implementation, and analog circuit design is still a challenge. As on today, very few, only one or two, topologies of opamps are implemented using CNFET. In this paper, first attempt is made, to the best of our knowledge, to design CNFETbased folded cascode opamp (CNFETFCOA) and successfully calculate almost all parameters associated with an opamp. Further different signal processing applications are implemented using novel folded cascode opamp (FCOA) designed using CNFET at 32 nm CNFET technologies. Next section explains about the design of CNFETFCOA.
3. Design of Folded Cascode opAmp Using Carbon Nanotube Field Effect Transistor
A CNFET works on the fundamental concept of applying gate voltage to modulate the current between drain and source and exhibits unipolar behaviour. In backgated structures, due to different junction and overlap capacitances, highfrequency operation is limited but the topgate edifice of CNFET permits highspeed operation. Also, due to inbuilt channel of nanotubes and its structure, leakage current is no longer the problem with CNFET and it shows enhanced current handling competency [24–26]. CNFET endeavours remarkable carrier transport and conduction characteristics predominantly due to the high mobility and high current density [25–27]. The width of the CNFET transistor (W), the diameter of CNT (), number of CNTs in the channel (N), the spacing between two adjacent nanotubes, and pitch (S) [13, 19, 22–26] are related by the following equation:
In CNFETbased implementation, number of tubes, pitch, and diameter are the parameters that are designed to achieve optimum result unlike aspect ratios in case of CMOS [2, 3, 28–30]. Figure 3(a) shows the schematic of proposed CNFETFCOA, and Figure 3(b) shows the symbolic representation of proposed CNFETFCOA.
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In this analysis, unlike conventional opamp, it is presumed that the current from Q1 directly flows through the drain of Q6 and thus to the load capacitance and the current from Q2 goes indirectly through Q5 and the current mirror consisting of Q7 to Q10. Also, it is assumed that maximum amount of current flows through Q1 and hence these two paths have slightly different transfer functions. The highfrequency poles and zeros are nondominant and can be ignored because they are located at high frequency compared to unity gain frequency [7].
An approximate smallsignal transfer function for the foldedcascode opamp in CMOS technology is given bywhere is the amplifier’s transconductance gain and is the output impedance.
The open loop gain of opamp is further calculated aswhere is the output impedance of the opamp and is the load capacitance.
For high frequencies, the load capacitance dominates, and hence
The input transconductance can be increased by using longchannel transistors and ensuring that the input transistor pair’s bias current is significantly larger than the cascode transistor’s bias current. This will also result in improvement of bandwidth. To maximize the dc gain of the designed opamp, it is considered that the current flowing through all the transistors connected to output node is at small levels. This will not only maximize the input transconductance but also output impedance. Maximum amount of bias current through the input differential pair results in large transconductance of the input devices and hence in the improvement of thermal noise performance of OpAmp [7, 31].
In this work, MOSFETlike CNFETs are used for designing the FCOA circuit and due to the similarities between the MOSFET and MOSFETlike CNFET devices in terms of IV characteristics and the other inherent attributes, design procedure of CNFETbased circuits is similar to CMOS [13, 30–37]. Furthermore, as in CNFET device μn = μp and all of the characteristics of the used CNFETs such as gate length (L = 32 nm), CNT diameters (DCNT = 1.49 nm), and pitch (8 nm), except the width of the CNFETs, are set to be identical, the only parameter here that could affect the gain of the FCOA is the width of CNFETs. In addition, because of the direct relation between the width of a CNFET and the number of its nanotubes [38], the desired widths can be set by adopting proper number of CNTs for each transistor [37].
For simulation purposes, CNFET, SPICE compatible Stanford University 32 nm CNFET model is used [30]. In this study, topgated undoped semiconducting MOSs like CNFETs with 4 nm thick HfO2, highk dielectric (k = 16), chirality (19, 0), and fixed diameter at 1.49 nm are used. The number of tubes is calculated using Equation (1) for pitch equals to 8 nm, keeping the diameter constant, and is itemized in Table 1. The designed folded cascode opamp configuration is further simulated using HSPICE to achieve satisfactory DC performance and further used to calculate various performance metrics such as DC gain (Av0), phase margin (PM), unity gain bandwidth (UGB), common mode rejection ratio (CMRR), power supply rejection ratio (PSRR), slew rate (SR), output swing (OS), and power consumption [6].

3.1. Optimum Choice for Pitch and Diameter of CNFET
The simulations are performed for three different values of pitch 8 nm, 12 nm, and 20 nm for CNFETbased FCOA. Table 2 shows the comparative results at different values of pitch with respect to specifications. The comparative examination of the important parameters of CNFETFCOA architectures affirms that a noteworthy improvement in performance is achieved in the CNFETbased FCOAs and the gain is highest amongst three for pitch equals to 8 nm. The similar kind of performance is not possible at such very deep submicron levels using CMOS due to extreme shortchannel effects, lithographic limitations, process variations, leakage current, and sourcetodrain tunneling [25, 37–41]. Further CNFET technology can also be easily clubbed with the bulk CMOS technology on a single chip and utilizes the same infrastructure [23, 30, 42].

An investigative result demonstrates that the frequency response of the designed OTA improves with the increase in diameter of the nanotube as shown in Figures 4(a) to 4(c). This is due to the fact that the transconductance goes up with the increase in diameter of the nanotubes. The DC gain decreases with the diameter because the reduction in the output resistance with diameter is more than the rise in its transconductance. This trend is observed because CNFET circuit performance and electrical behaviour directly depend on the CNT diameter. Diameter is the main parameter that affects the on current proportionally in a CNFET apart from barrier height at the S/D contact (or RS/D), chirality, and oxide thickness, but for larger diameters, current tends to saturate due to large screening and scattering effects [14, 24, 25, 33]. Also, the power consumption of an amplifier goes up due to the smaller band gap and higher current drive.
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4. CNFETFCOABased Analog Signal Processing Applications
Operational amplifier was formerly aimed to execute different operations on signals such as addition, subtraction, differentiation, integration, and comparison. In the proposed work, the functionality of the CNTFETFCOA is tested for all such signal processing applications to check the practical usefulness of the proposed CNFETFCOA at very deep submicron node. All the signal processing circuits are designed and implemented at 32 nm, a nanometer regime where there are certain constraints with CMOS technology due to sternness of nonideal effects.
4.1. CNFETFCOABased Noninverting Amplifier
The opamp circuitry, comprising voltage divider at inverting node, is called a noninverting amplifier because its voltage gain is positive [30]. This means that the output voltage will follow the input voltage. The period of input and output voltage is same as the phase, only amplitude of output waveforms depends on gain of the opamp. CNFETFCOAbased noninverting amplifier is shown in Figure 5(a). The input voltage V_{in} is applied to the noninverting terminal of opamp. Partial output, i.e., feedback, is given to the inverting input through the feedback resistor R_{F}, which forms voltage divider network with R_{in1}. For the designed noninverting amplifier, voltage gain is 14. The expression for output voltage is given by using Equation (10) and its waveform is shown in Figure 6(a):
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4.2. CNFETFCOABased Inverting Amplifier
As the name suggests, input and output waveforms are out of phase or are having 180° phase shift, i.e., whenever input voltage increases, output voltage decreases and viceaversa. The circuit diagram of a CNFETFCOAbased inverting amplifier is shown in Figure 5(b). The input signal, V_{in}, is applied through resistor R_{in1} to the inverting terminal of the opamp. Feedback resistor R_{F} connects the partial output to the noninverting input. Second input of the opamp is connected to fixed potential, say ground. For the designed inverting amplifier, voltage gain is 14 and the expression for output voltage of the inverting amplifier is as shown by Equation (11) and the resulting waveform is shown in Figure 6(b):
4.3. CNFETFCOABased Summer
As the name suggests, summer means the circuit which adds two signals [30]. Figure 5(c) shows the basic inverting summer which is used to sum two or more signal voltages and at the output produces amplified sum of the two input signal. For the designed non inverting summer, the expression for output voltage is given by Equation (12), and the waveform is as displayed in Figure 6(c):
4.4. CNFETFCOABased Subtractor
A differential amplifier with unity gain can be used to provide an output voltage that is equal to the difference of two input voltages [30]. Such a circuit is called a subtractor and is shown in Figure 5(d). The net output result, as shown in Figure 6(d), is the difference between two input voltages V_{in1} and V_{in2} applied at the inverting and noninverting terminals of the opamp, respectively [40]. For the designed subtractor, voltage gain is 1, since all the resistors are of same value, and the output voltage of the subtractor is evaluated using the following equation:
4.5. CNFETFCOABased Differentiator
In differentiator, the output voltage is proportional to the rate of change of its input voltage. Figure 5(e) gives the circuit diagram of a CNFETFCOAbased differentiator. The circuit consists of input resistor R_{in} in series with capacitor C_{in} and pair of R_{F} and C_{F} in parallel in the feedback path. For the designed differentiator, output voltage is expressed by Equation (14). Figure 6(e) shows the corresponding output of differentiator:
4.6. CNFETFCOABased Integrator
In case of integrator, output voltage is proportional to the integration of its input voltage [30]. The circuit for the integrator can be as same as that of the differentiator, except that the position of the resistor and that of the capacitor is interchanged as shown in Figure 5(f). For the designed integrator, output voltage is expressed as shown in Equation (15). The corresponding inputoutput waveforms are shown in Figure 6(f):
4.7. CNFETFCOABased HalfWave Rectifier
Halfwave rectifier (HWR) is a circuit which allows only the positive cycle of input sinusoidal waveform with the help of forwardbiased diode to reach at the output. Such a circuit of halfwave rectifier is shown in Figure 5(g). The opamp output turns out to be positive only during the positive half cycle of the input waveform, which eventually makes the diode D1 forward biased and the positive half cycle waveform appears across the output terminal [30]. In contrast, during the negative half cycle, the opamp output becomes negative, turning OFF diode D1. This will not allow the negative portion of input to appear across the output. The overall outcome is impeccable halfwave rectification, as epitomized in Figure 6(g).
4.8. CNFETFCOA FullWave Rectifier
In contrast to halfwave rectifier, fullwave rectifier allows positive as well as negative half cycles of input waveforms to reach at the output one after the other sequentially. Such a fullwave rectifier circuit is shown in Figure 5(h), which is actually the combination of two halfwave rectifier circuits. This is achieved using two different opamps A1, A2 and diodes D1, D2. The opamp A1 output turns out to be positive only during the positive half cycle of the input waveform. V′ becomes negative which eventually turns ON the diode D1 [41]. The voltage at the inverting terminal of A2 appears at the output, which is equal to the input, due to the virtual ground at the two input terminals of opamp A2. Consider now the negative cycle of the input waveform. In this case, the V′ will be positive, making diode D1 OFF and D2 ON. Due to the virtual ground at the inverting input of opamp A1, V2 = V1 = V [43]. This causes output voltage to be equal to the negative of the input voltage at A1 and thus positive. Therefore, outputs during two half cycles are same and fullwaverectified output voltage is obtained as shown in Figure 6(h).
4.9. CNFETFCOABased Clipper
As the name suggests, a clipper is a circuit that can remove certain portions of the input waveform near the positive or negative peaks, i.e., it avoids the output from going beyond a predetermined voltage level without adversely affecting the residual part of the input waveform. If such a circuit is implemented using opamp, a diode is used at the output of opamp, to remove off some portion of the input signal. CNFETFCOAbased positive clipper is shown in Figure 5(i). This type of circuit confiscates negative peak of the input signal. The value of reference voltage V_{ref} decides the clipping portion. The positive input gets grounded initially when the V_{ref} is zero. Whenever input V_{in} is positive, the output will follow the input V_{in}, since the opamp output becomes positive, turning ON the diode. The opamp output will go negative during negative half cycle of the input. In this case, the final output V_{o} will follow the negative half cycle of the input till the input voltage is greater than the reference voltage only. Hence the portion of the negative half cycle will be clipped for which input voltage becomes less than the reference voltage. In order to adjust the clipping level, V_{ref} needs to be adjusted as per requirement.
4.10. CNFETFCOABased Clamper
By using clamper circuits, the output is shifted up or down to a preferred DC level, i.e., a predetermined DC level is added to the input voltage. A variable DC level CNFETFCOAbased clamper circuit is presented in Figure 5(j). This is a positive clamper because the input waveform is clamped at +V_{ref} [41]. In this case, both AC and DC input voltages need to be applied and output of the clamper is a net result of AC and DC input voltages applied to the inverting terminal, and a potentiometer is connected to noninverting input terminals to vary V_{ref}. Initially, ponder +V_{ref} at the noninverting input. The output voltage (V_{o}) will also be positive, which turns ON the diode D1 completing the feedback loop. The opamp then works as a voltage follower, since capacitor C1 blocks DC voltage and V_{o} becomes equal to V_{ref}. Now, consider the voltage V_{in} at the inverting input. During its negative half cycle, capacitor C1 will charge to the negative peak value of the voltage (V_{P}) since diode D1 starts conducting. The peak voltage (V_{P}) across the capacitor acquired during the negative half cycle is retained because diode D1 turns OFF during the positive half cycle of V_{in} [40]. The output peak voltage V_{o} becomes equal to 2V_{P}, since this voltage V_{P} is in series with the positive peak voltage V_{P}. Thus, the net output is V_{o} = V_{ref} + V_{P}; so, the negative peak of 2V_{P} is at Vref. The input and output waveforms are shown in Figure 6(j).
4.11. CNFETFCOABased Comparator
As the name suggests, a comparator is a circuit that compares input signal at one terminal of opamp with a known reference voltage at the other input of opamp. Figure 5(k) shows CNFETFCOAbased comparator. Consider a fixed reference voltage V_{ref} of +1V at the inverting input and the other timevarying signal V_{in} is applied to the noninverting input. This type of comparator is called as noninverting comparator. When input voltage V_{in} is greater than reference V_{ref}, output voltage V_{o} reaches to +V_{sat} and when V_{in} becomes less than reference, V_{o} changes towards −V_{sat}. Thus, V_{o} varies from one level to another level whenever input increases or decreases with respect to V_{ref} as shown in Figures 6(k) and 6(l). Hence, this circuit is also termed as “voltage level indicator.” Such inverting, noninverting comparators are needed to interface analog and digital blocks in mixed signal applications.
4.12. CNFETFCOABased Peak Detector
As the name suggests, a peak detector is a circuit which detects the peak value of applied input signal [41, 43] as shown in Figure 5(m). This circuit detects the positive peak of the input signal. CNFETFCOAbased peak detector consists of a series connection of a diode and a capacitor. The capacitor C1 gets charged to the peak value V_{pp} of the input voltage, whenever diode D1 becomes forward biased during every positive half cycle of the input. On the contrary, the charge/voltage across capacitor is retained during every negative half cycle of the input, since the diode D1 is nonconducting and the only discharge path for C1 is through the output terminal V_{o} [41, 43]. Thus, the capacitor retains the peak value even as the waveform drops to zero.
4.13. CNFETFCOABased Zero Crossing Detector
As the name suggests, a zero crossing detector or ZCD is a circuit used to detect a zero crossing condition of input sinusoidal waveform during transition from positive to negative and viceaversa. The circuit is similar to the comparator except that the reference voltage is fixed and its value is permanently zero. Figure 5(n) shows inverting comparator with input as sinusoidal waveform. The corresponding inputoutput waveforms are shown in Figure 6(n).
Output of the ZCD, Vo, will be at positive saturation voltage +V_{sat} for the values of input waveform greater than zero and will be at negative saturation voltage −V_{sat} when input signal amplitude is less than zero. Every time when the output of opamp changes from +V_{sat} to −V_{sat}, the capacitor C charges to +V_{sat} and if the output of opamp transits from −V_{sat} to +V_{sat}, capacitor discharges through R1 to −V_{sat}. Whenever the square wave crosses zero voltage, the arrangement of C1 and R1 generates an output comprising of peaks at that time interval. The diode is used to remove the peaks at the zero crossings whenever input voltage crosses zero voltage in increasing direction.
The resulting waveforms of all the above applications are shown in Figure 6.
5. Conclusions
In this work, we designed and simulated folded cascode operational amplifiers (FCOA) using promising CNFET technology at 32 nm, a very deep submicron technology node, at 1 V power supply voltage. The relative exploration has discovered that the CNFETbased FCOAs have beaten the CMOSbased FCOAs extensively in the nanometer regime. The conventional CMOS technology is unable to produce significant gain due to the stringent nonideal effect in nanometer regime. Further, the stability analysis have revealed the CNTFETbased FCOA to be exceedingly stable.
The novel CNFETFCOA is further used to develop analog signal processing circuits such as noninverting amplifier, inverting amplifier, summer, subtractor, differentiator, integrator, halfwave rectifier, fullwave rectifier, clipper, clamper, comparator, peak detector, and zero crossing detector. All these circuits are successfully implemented and are found considerably competent than that of conventional CMOSbased circuits in nanoscale regime. It has also been proved from simulation results that CNFET is a promising nanodevice especially for lowpower analog circuit applications at very deep submicron technology nodes.
Data Availability
Any data and information used to support the findings of this study will be provided upon request to the corresponding author.
Conflicts of Interest
The authors declare that there are no conflicts of interest regarding the publication of this paper.
Acknowledgments
The authors would like to thank Dr. A. M. Fulambarkar, Dr. N. B. Chopade, and Dr. Sheetal Bhandari, Pimpri Chinchwad College of Engineering, Pune, India, for their support and encouragement. They would also like to thank Dr. G. C. Patil, Visvesvaraya National Institute of Technology, Nagpur, India; Dr. M. B. Mali, Sinhgad College of Engineering, Pune, India; Prof. Ketan Raut, Vishwakarma Institute of Information Technology, Pune, India; and Dr. Shailaja Patil, JSPM's Rajarshi Shahu College of Engineering, Pune, India, for many useful discussions and their continuous guidance throughout the work.
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Copyright © 2018 Varsha S. Bendre et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.