Multifunctional high-frequency circuit capabilities of ambipolar carbon nanotube FETs

TL;DR

This paper demonstrates the design of high-frequency circuits using ambipolar carbon nanotube FETs, enabling configurable amplification and frequency doubling with stable matching networks and detailed analysis of device imperfections.

Contribution

It introduces a compact transistor model for ambipolar CNTFETs to create multifunctional HF circuits with configurable modes and analyzes their performance and robustness.

Findings

Achieved 4.5 dB and 6.7 dB gain at 2.4 GHz in PCA modes

Demonstrated frequency doubling with 20 dBc harmonic suppression

Studied effects of metallic tubes and non-ideal inductors on performance

Abstract

An experimentally-calibrated carbon nanotube compact transistor model has been used here to design two high-frequency (HF) circuits with two different functionalities each: a phase configurable amplifier (PCA) and a frequency configurable amplifier (FCA). The former design involves an in-phase amplifier and an inverting amplifier while the latter design embraces a frequency doubler as well as a distinct inverting amplifier. The specific functionality selection of each of the two HF circuit designs is enabled mainly by the inherent ambipolar feature at a device level. Furthermore, at a circuit level the matching networks are the same regardless the operation mode. In-phase and inverting amplification are enabled in the PCA by switching the gate-to-source voltage (VGS) from -0.3 V to 0.9 V while the drain-to-source voltage (VDS) remains at 3 V. By designing carefully the matching and stability networks, power gains of 4.5 dB and 6.7 dB at 2.4 GHz for the in-phase and inverting operation mode have been achieved, respectively. The FCA, in its frequency doubler operation mode, exhibits 20 dBc of fundamental-harmonic suppression at 2.4 GHz when an input signal at 1.2 GHz is considered. This frequency doubler functionality is enabled at VGS=0.3 V, whereas at VGS=0.9 V amplification of 4.5 dB is obtained while VDS remains at 3 V in both cases. In both configurable circuits the stabilization and matching networks are the same regardless the bias-chosen operation mode. The circuits performance degradation due to metallic tubes in the device channel is studied as well as the impact of non-ideal inductors in each design. PCA and FCA operation modes are further exploited in high-frequency modulators.