A major problem of large signal compact modelling of bipolar transistors (BJT) at radio frequencies is the inconsistency of the static and dynamic behaviour of the model. The quasi-static assumption is not accurate, and the physical operation of a BJT has many different modes. It is difficult to find a compact equivalent circuit topology which is valid for all regions of operation such as low injection, high injection, avalanche breakdown, saturation and quasi-saturation. A smooth transition from one region to another maintaining charge conservation and continuous derivatives of the non-linear circuit functions becomes a major problem. In practice, the classical SPICE Ebers-Moll (SEM) and Gummel-Poon (SGP) models with minor dynamic extensions are widely used in radio frequency design including heterojunction bipolar transistor (HBT) circuits. A summary of these models and of one new large signal BJT model, VBIC95 is given.
Non-linear dynamic modelling of RF bipolar transistors, Page 1 of 2
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