# A High-Gain CNTFET-Based LNA Developed Using a Compact Design-Oriented Device Model
## 1 Introduction  
Carbon nanotube field-effect transistors (CNTFETs) have demonstrated the ability to be suitable for mixed-signal and RF application, with respect to both conventional bulk semiconductors and 2-D materials, such as graphene [1, 2, 3, 4, 5, 6]. This is due to the fact that the 1-D transport in carbon nanotubes (CNTs) leads not only to a low scattering rate and high current-carrying capability but also to a linear \(I_{D}\) vs. \(V_{GS}\) transcharacteristic under some conditions [7, 8, 9]. This I-V behavior could be considered an advantage in future mobile communication systems where increasingly complex modulation techniques are expected to be used [10]. In particular, RF systems performance mainly depends on their frontend circuit components, such as the low-noise amplifier (LNA), high power amplifier (HPA), single-pole-double-throw (SPDT) switch, oscillator, and mixer. The design of these building blocks is usually implemented through circuit simulators that use compact models representing the actual devices of a given technology. Thus, the need for compact models is of paramount importance for analog RF design where the requirements are quite stringent since the models must accurately describe typically nonlinear devices over a wide range of frequencies, biases, and temperatures. On the one hand, the device model should be sophisticated enough to take into account the device behavior in different working regions. In particular, the design of RF frontends, including LNAs and HPAs, requires the accurate prediction of (i) the small-signal behavior (that must also include noise) for which the first derivative of the currents and charges with respect to terminal voltages must be correctly modeled, and (ii) large-signal time-domain behavior (along with phase noise) and nonlinear distortion for which an accurate modeling of currents and charges up to at least the fifth-order derivatives is needed. On the other hand, the device model should be compact and simple enough in order to allow reasonable circuit simulation times. As a consequence, the physical relationshipsdescribing the device behavior must be as simple as possible, e.g., distributed regions of the device have to be represented by lumped elements, and complicated physical effects have to be expressed through simple and explicit analytical solutions [11; 12]. Several models have been proposed in the literature that try to approximate the real behavior of the CNTFET device, maintaining their mathematical and computational complexity as low as possible [13; 14; 15; 16; 17; 18; 19; 20; 21]. The goal of this paper is to develop a compact and design-oriented device model that is able to describe the device behavior with sufficient details so as to ease the implementation of the main RF building blocks, such as LNA, HPA, and SPDT switch. Nowadays, the increasing demand for wireless communication systems for broadband, multi-band, and multi-standard receivers makes the bandwidth a critical issue in the design of LNAs [22; 23; 24; 25; 26; 27; 28]. Large bandwidth systems exhibit desirable advantages, such as large transmission channel capacity, less multipath fading effect, and easier material penetration. As the first stage of a receiver system, the LNA should have very low noise and provide reasonable voltage gain over the wide band of interest so that the total noise of the receiving chain can be suppressed. In addition, wideband input matching and high linearity also need to be guaranteed. Furthermore, low power consumption and small die area can increase the battery life and decrease the chip cost [29]. Usually, voltage-mode LNAs have many drawbacks, such as limited bandwidth, the need for a high supply and the requirement of a current-to-voltage conversion stage due to the existence of high-impedance nodes. Current-mode LNAs have many intrinsic advantages over voltage-mode counterparts, including low supply voltage requirements, wide bandwidth, tunable input impedances, and high slew rates.