Transconductance

This paper describes about different types of voltage followers. Each follower has its own advantages and limitations. The voltage follower can be characterized with current mirror source current or it can be used as a ideal current source. Voltage Follower is one of the most important analog circuits required in many analog integrated circuits. Input impedance of op amp is very high, giving effective isolation of the output from the signal source.

This paper discusses a comprehensive analytical study of electrical properties of sin-gle‐wall conventional carbon nanotube field‐effect transistor (CNTFET) devices of subthreshold swing (SS), transconductance (g m), and extension resistance. The analytical expressions for SS and g m have been derived based on channel modulated potential. In the study, it was observed that SS value of the CNTFET device is equal to 60 mV/decade, which is smaller than the conventional and double gate metal‐ oxide‐semiconductor field‐effect transistors. The subthreshold swing degrades at larger tube's diameter and gate‐source voltage due to increased source‐drain leakage current. Carbon nanotube field‐effect transistor devices achieve larger g m at large gate‐source voltage, which has a disadvantage of reducing the allowable voltage swing at the drain. The extension resistance of the device falls with diameter of the tube. The subthreshold swing (SS) is the important parameter to sustain the scaling of silicon transistor because leakage power is strongly influenced by SS of the device. Subthreshold swing value indicates the minimum gate‐source voltage (V gs) required to lower the subthreshold current by a factor of 10. Steep SS devices are of great interest due to demand of power and energy‐efficient digital circuits. As metal‐oxide‐semiconductor field‐effect transistors (MOSFETs) scaled below 45 nm, the subthreshold leakage current becomes more significant due to short‐channel effects (SCEs), parameter variations, 1-3 and strong coupling between temperature and subthreshold leakage current. 4,5 The fundamental thermodynamic limit on the minimum operational voltage and switching energy of the conventional FETs is ideally 60 mV/decade at room temperature, but in practice , the gate oxide screens the gate fields and the coupling between the gate and channel is not perfect, which causes SS to be larger than the ideal value. 6-10 The carbon nanotube FET (CNTFET) is a promising candidate for future electron devices, and rapid progress in this field has made it possible to fabricate CNTFET‐based integrated circuits. In facts, CNTFET is the substitute of silicon MOS due to excellent control of SCEs 11-13 as well as physical and electrical properties. 14,15 Although the SS of the CNTFET device has been reported theoretically by researchers, 16-18 this parameter has not been discussed in detail compared with the other parameters. In nanotube junctions, the parasitic resistance (R P) is given as the sum of contact resistance (R C) and the extension resistance (R ext). The R ext contributes more in the R P than in the R C. Lower R ext improves the intrinsic performance of the device. 19 In the literature, less attention has been given on the study of R ext compared with R C. 20 In this paper, we studied the SS and R ext of CNTFET after using our previously derived drain current equation. 15 The SS is close to 60 mV/decade at room temperature in CNTFET device. We have also observed that the SS of the CNTFET device is

This paper presents a highly adaptive operational amplifier with high gain, high bandwidth, high speed and low power consumption. By adopting the recycling folded cascode topology along with an adaptive-biasing circuit, this design achieves high performance in terms of gainbandwidth product (GBW) and slew rate (SR). This single stage op-amp has been designed in 0.18μm technology with a power supply of 1.8V and a 5pF load. The simulation results show that the amplifier achieved a GBW of 335.5MHz, Unity Gain Bandwidth of 247.1MHz and a slew rate of 92.8V/μs.

The influence of hetero dielectric gate oxide and work function engineering on DC and Analog/RF performance of dual material hetero dielectric double gate tunnel field-effect transistors (DMHDDGTFET) is investigated in this research. We examined an optimised hetero gate dielectric to reduce ambipolar current conduction, leakage current, and boost ON-current for this purpose (ION). In addition, the entire gate electrode of the proposed device structure DMHDDGTFET has consisted of three sections named as tunneling gate (M1) with work function (ϕ1), control gate (M2) with work function (ϕ2), and auxiliary gate (M3) with work function (ϕ3). To preserve dual work functionality, all possible arrangements of these work functions were incorporated. The technology computer-aided design (TCAD) simulations were carried out for these probable arrangements and matched with single material hetero dielectric double gate tunnel field-effect transistor (HDDGTFET) and conventional double gate TFET (ϕ1 = ϕ2 = ϕ3). Simulation results show that the work function grouping (ϕ1 = ϕ3 < ϕ2) provides better device performance such as improved switching characteristics and sub-threshold slope (SS). Further, based on the utmost performed work function combination the analog/RF performance analysed. This work shows improved analog/RF parameters like transconductance (gm), the gate to source capacitance (Cgs), the gate to drain capacitance (Cgd), and cut-off frequency (fT). The influence of incorporating hetero dielectric and work function engineering shows a significant enhancement in ON-state current ION (1.93 × 10−4 A/μm) and lower leakage current IOFF (2.49 × 10−17 A/μm), ION/IOFF (7.76 × 1012), smaller subthreshold swing SS (6.8 mV/decade), higher transconductance (1.12 ms) and cut-off frequency (228.4 GHz) making this device suitable for low power and high-frequency applications.