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在晶体管模型和电路分析中,Early电压的概念已被广泛应用。本文讨论了任意基区晶体管Early电压的物理关系,导出了恒流驱动条件下的Early电压V_(A(I))与恒压驱动条件下的Early电压V_(A(V))之间的表达式,考虑了发射结势垒复合对V_(A(I))和基区少子电荷对V_(A(V))的影响。结果表明,由于基区校正因子的存在和V_(A(V))随电流的变化,通过开路与短路输出阻抗的测量来估计晶体管的注射效率与基区输运系数是有疑问的。文中指出在电路设计中应用Early电压必须十分谨慎。
The concept of Early voltage has been widely used in transistor model and circuit analysis. In this paper, we discuss the physical relationship of Early voltage of arbitrary base transistor, and derive the expression of Early voltage V_ (A (I)) under constant current and Early voltage V_ (A (V)) under constant voltage. The effect of the combination of emitter junction barrier on V_ (A (I)) and the minority carrier charge on V_ (A (V)) is considered. The results show that due to the existence of base-area correction factor and the change of V_ (A (V)) with current, it is doubtful to estimate the injection efficiency of the transistor and the base transport coefficient by measuring the open-circuit and short-circuit output impedance. The article pointed out that the application of Early voltage in the circuit design must be very cautious.