In this paper, novel carbon nanotube (CNT) based operational transconductance amplifiers (OTAs) have been designed and simulated. Three types of CNT-based OTAs have been designed at 45 nm technology node and have been compared with the conventional CMOS-based OTA. The comparative analysis of the key characteristics of all the devices has revealed that a significant improvement in performance is observed in the CNT-based OTAs, particularly in a pure CNT-OTA. In the pure CNT-OTA, DC gain has increased by 218%, slew rate has increased by 22.58%, the output resistance has increased by 55.2% and the power consumption is ∼ 193 times less in comparison to the conventional CMOS-OTA. Further, common mode rejection ratio (CMRR) and power supply rejection ratio positive (PSRR+) has increased by 31.87% and 136.3%, respectively in pure CNT-OTA. The performance of CNT-based OTAs has also been studied thoroughly by varying the number of CNTs (N), CNT pitch (S) and the diameter of CNTs (D CNT ) at 0.9 V. It has been observed that their performance can be improved further by using optimized values of CNT number; inter CNT-pitch and diameter. The stability analysis has shown that the pure CNT-OTA is highly stable. A 16.7% and 4% increase in phase and gain margins is achieved in the pure CNT-OTA in comparison to the bulk CMOS OTA. Finally, band and high pass filters have been realized by using the proposed CNT-based OTAs.

In this work, design and calibrated simulation of carbon nanotube field effect transistor (CNTFET)-based cascode operational transconductance amplifiers (COTA) have been performed. Three structures of CNTFET-based COTAs have been designed using HSPICE and have been compared with the conventional CMOS-based COTAs. The proposed COTAs include one using pure CNTFETs and two others that employ CNTFETs, as well as the conventional MOSFETs. The simulation study has revealed that the CNTFET-based COTAs have significantly outperformed the conventional MOSFET-based COTAs. A significant increase in dc gain, output resistance and slew rate of 81.4%, 25% and 13.2%, respectively, have been achieved in the proposed pure CNT-based COTA in comparison to the conventional CMOS-based COTA. The power consumption in the pure CNT-COTA is 324 times less in comparison to the conventional CMOS-COTA. Further, the phase margin (PM), gain margin (GM), common mode and power supply rejection ratios have been significantly increased in the proposed CNT-based COTAs in comparison to the conventional CMOS-based COTAs. Furthermore, to see the advantage of cascoding, the proposed CNT-based cascode OTAs have been compared with the CNT-based OTAs. It has been observed that by incorporating the concept of cascode in the CNTFET-based OTAs, significant increases in gain (12.5%) and output resistance (13.07%) have been achieved. The performance of the proposed COTAs has been further observed by changing the number of CNTs (N), CNT pitch (S) and CNT diameter (DCNT) in the CNTFETs used. It has been observed that the performance of the proposed COTAs can be significantly improved by using optimum values of N, S and DCNT.

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