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Even-odd symmetry and the conversion efficiency of ideal and practical graphene transistor frequency multipliers
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View: Figures


Image of FIG. 1.
FIG. 1.

(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.

Image of FIG. 2.
FIG. 2.

(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.

Image of FIG. 3.
FIG. 3.

(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.

Image of FIG. 4.
FIG. 4.

(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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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Even-odd symmetry and the conversion efficiency of ideal and practical graphene transistor frequency multipliers