Complementary two-transistor circuits and negative differential resistance

The DC behavior of nonlinear one-ports using two complementary Ebers-Moll-modeled transistors and lacking internal independent sources is discussed. It is proven that, in the absence of internal resistors, all such one-ports-irrespective of their internal topology and transistor parameter values-cannot exhibit negative differential resistance (NDR) for any value of an external biasing current source. One circuit using two complementary transistors and no resistors is of particular interest, since it is often cited as a two-transistor simplified model for silicon-controlled rectifier devices. The results demonstrate that either the transistor behavior unaccounted for in an Ebers-Moll-type model must be involved in this one-port's NDR behavior, or the presence of internal resistors is essential to such a circuit's behavior having even a generally correct qualitative character.<
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