Characterizing Germanium Junction Transistors

Abstract

Transistors have provided the basis of modern electronics. Being relatively intricate devices, and often exhibiting intense parameter variation, this type of electronic devices has motivated much research interest especially regarding their characterization and modeling. In this work, we apply a recently reported modeling methodology, based on the Early effect, for characterizing new old stock NPN and PNP small signal germanium junction transistors and comparing them to more modern silicon bipolar junction devices. The Early approach is special in the sense that its two parameters, namely the Early voltage $V_a$ and a proportionality parameter $s$, are fixed and independent of transistor operation. Remarkable results are obtained, including the fact that the four considered groups, namely NPN and PNP germanium and silicon devices, occupy mostly non-overlapping regions in the Early parameter space, with PNP devices presenting larger parameter variability in both cases. Surprisingly, the considered germanium devices exhibited smaller parameter variability than observed for the silicon counterparts. When mapped into the more traditional space defined by the current gain and output resistance parameters, the four transistor groups exhibited much larger overlaps and yielded a clustering structure much less organized than allowed by the Early mapping. This result suggest that the Early representation of transistors is more compatible and inherently related to the structure of amplifying devices such as those considered in this work. In addition, it was verified that the center of mass of each of the NPN-PNP pairs of germanium and silicon devices are crossed by respective $\beta$-isolines for gains of 130 and 250, respectively. Germanium devices were also characterized as having smaller output resistance and smaller magnitudes of Early voltage.