Design of a High-Speed Transistor for the ASLT Current Switch

The evolution of a high-speed current switch transistor design is described from initial design considerations through final optimization of horizontal geometry. It was found that a very narrow geometry was desirable, in order to produce the desired low base resistance (∼40 Ω). Other characteristics of this design include low capacitance, well-controlled emitter forward voltage, and high-frequency cutoff. Compatibility with the SLT form factor assures manufacturability. This transistor when used in ASLT circuits yields circuit delays of 1.8 nsec.