Analysis of nonlinear behavior of power HBTs |
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Authors: | Woonyun Kim Sanghoon Kang Kyungho Lee Minchul Chung Jongchan Kang Bumman Kim |
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Affiliation: | Dept. of Electron. & Electr. Eng., Pohang Univ. of Sci. & Technol.; |
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Abstract: | To accurately understand the linear characteristics of a heterojunction bipolar transistor (HBT), we developed an analytical nonlinear HBT model using Volterra-series analysis. The model considers four nonlinear components: rπ, Cdiff, Cdepl, and gm. It shows that nonlinearities of r π and Cdiff are almost completely canceled by g m nonlinearity at all frequencies. The residual gm nonlinearity is highly degenerated by input circuit impedances. Therefore, rπ, Cdiff, Cdepl, and g m nonlinearities generate less harmonics than Cbc nonlinearity. If Cbc is linearized, gm is the main nonlinear source of HBT, and Cdepl becomes very important at a high frequency. The degeneration resistor RE is more effective than RB for reducing gm nonlinearity. This analysis also shows the dependency of the third-order intermodulation (IM3) on the terminations of the source second harmonic impedances. The IM3 of HBT is significantly reduced by setting the second harmonic impedances of ZS,2ω2 = 0 and ZS,ω2-ω1 = 0 |
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