IBM Research on Tuesday unveiled plans to create a "DNA transistor" that would result in personalized genetic testing for about $100 to $1,000.

In the early days, PNP bipolar transistors were common, but the bulk of circuits you see today use NPN transistors. As [Aaron Danner] points out, many people think PNP transistors are “backwa… ...

This made me look at the turn-off specs for the npn (a 2N2222A) and, for the first time I can remember, I noticed that the turn-off test circuit in the data sheet used a negative drive to the base.