Multifunctional High-Frequency Circuit Capabilities of Ambipolar Carbon Nanotube FETs

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 ($V_{\rm GS}$) from -0.3 V to 0.9 V while the drain-to-source voltage ($V_{\rm DS}$) remains at 3 V. By designing carefully the matching and stability networks, power gains of $\sim$4.5 dB and $\sim$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 $\sim$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 $V_{\rm GS}={0.3} $ V, whereas at $V_{\rm GS}={0.9}$ V amplification of $\sim$4.5 dB is obtained while $V_{\rm DS}$ 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.