Larry Nagel: The Early Bell Labs Years

Believe it or not, there were digital computer-based circuit simulation programs before SPICE (Simulation Program with Integrated Circuit Emphasis). In the mid-1960s, I was assigned to design a pair of junction field-effect transistor (JFET)-based voltage-variable attenuators for the Bell System 4G Speakerphone. The loss versus voltage curves of these two circuits were to be complementary: as the loss of one circuit increased, the loss of the other decreased, and close tracking was essential. Our primitive technology dictated that all JFET gates had to be connected together. One of the circuits looked like Figure 1.