Unknown IC on a TMS1000 board

Am 06.02.2012 10:44, schrieb Eric Smith: It is an academic issue. True, the electron mobility is different for holes and electrons, but it is not really the dominating factor. Consider Germanium has even higher electron/hole mobility values (3900 vs. 1900 cm^2/Vs) than silicon, but this doesn't make it a better semiconductor material per se. Historically, germanium point contact transistors were mainly PNP for production reasons, this changed to the reverse when mesa and planar transistors based on silicon came up. This is because SiO2 makes up a better insulator than GeO2. For paired PNP/NPN transistors (e.g. complementary transistors on the same die), one could expect a slightly higher h21fe and higher Ic for the NPN part for a given matching Ube curve, but whether this is relevant at all depends on the application. Usually, it isn't relevant, and for single transistors, you can typically find a PNP with the same or better characteristics than a given NPN. This was different, again, historically, with Ge transistors having an fT in the kHz range. And for extreme conditions, e.g. very high frequency or very high power switching, one would nowadays no longer consider bipolar transistors at all, but various types of MOSFETs. -- Holger