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(Color online) Transport characteristics of an ideal FET frequency doubler possessing even-odd symmetry. (a) Standard frequency multiplier circuit. Zin = RL = 50 Ω for RF/THz systems. The L and C networks are employed to route DC and AC signals separately. For an ideal FET, Rc = 0 Ω. (b) Parabolic even symmetry about the Dirac point. (c) Odd symmetry owing to linear charge transport.
(Color online) Performance of an ideal FET with even-odd symmetry. (a) Maximum conversion efficiency as a function of normalized resistance. Equation (3) (analytical) shows good agreement with rigorous harmonic balance (HB) simulation with differences ∼15%. Using material constants similar to those found in graphene, the maximum conversion efficiency achieved is η o = 14.3, indicating that power gain is achievable with VDS = 0.5 V. (b) Output spectrum at η max = η o (Ro ≈ 4 Ω, RL = 50 Ω) showing the exclusive presence of only even harmonics with perfect rejection of odd harmonics, a benefit of the even-odd symmetry of the ideal FET doubler.
(Color online) (a) Qualitative transport profile of an intrinsic GFET highlighting the three regions of charge distribution and transport. S and D are the source and drain ends of the channel, respectively. Regions I and II have been previously discussed.16,17 To maintain electron-hole symmetry and efficient frequency doubling, the Dirac point is in region III (VG = VD/2). (b) Non-idealities such as high Rc obscures the intrinsic GFET current saturation and degrades performance. The simulated GFET has mobility of 5000 cm2/Vs, Cox = ½Cqo , Ro = 7.8 Ω, W/L = 100 μm/0.1 μm, and VG = 0.3 V.
(Color online) (a) Conversion gain of an intrinsic GFET. The small-signal slope is 10 dB/decade, characteristic of square-law multipliers. (b) Output spectrum showing the presence of odd harmonics owing to the non-linear ID − VD response. (c) Aggressive scaling of Cox and mobility increase the efficiency with capacitance scaling having greater influence. (d) The negative impact of Rc and impurity carriers (inset) on the conversion gain.
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