In this paper, we present an analytical approach for the study of the small-signal response of nanometric field-effect transistor at terahertz frequencies. One-dimensional hydrodynamic equations coupled with a pseudo-two-dimensional Poisson equation are derived at first-order to obtain the small-signal admittance matrix describing the transistor. This matrix is then used to model the loaded device and establish its voltage amplification. The admittances and voltage amplification spectra exhibit sharp resonances associated with the plasma modes of the channel. The influences of the device geometry, operating temperature and connected load are investigated.Index Terms-Nanometric field-effect transistor (FET), resonances, small-signal admittance, terahertz (THz).
An analytical model of the high-frequency noise of frequency multipliers based on Schottky-barrier diodes (SBD) operating in series with a parallel resonant circuit under large-signal conditions is developed. Such a model, on one hand, takes into account the main intrinsic features of the SBD noise related to shot-noise, returning carriers, plasma resonance at n+n homojunctions, and, on the other hand, it incorporates the SBD noise spectrum modifications induced by the output resonant circuit. It is shown that the SBD embedding into an external circuit can produce the appearance of an extra noise due to up-down conversion of the fluctuations of the voltage drop between the SBD terminals originated by a periodic modulation of the varactor capacitance by the pumping signal.
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