6.1 Introduction – Pulse and Digital Circuits


Active devices such as semiconductor and Zener diodes, transistors and FETs can be used as static switches. To use these switches for high-speed applications, it is necessary to know the influence of inter-electrode capacitors on the switching speed of these devices. For transistors, the switching speed can be improved with the use of speed-up capacitors and expressions for the switching times of a transistor are derived to calculate the turn-on and turn-off times of a transistor. Further, the choice of the supply voltage depends on the breakdown voltages of the transistor and the saturation parameters of the transistor are temperature dependent. The influence of temperature on these parameters is discussed in this chapter. Finally, a transistor switch with inductive or capacitive loads is considered and also the application of a transistor switch as a latch. In most applications, the ON transistor is driven into saturation. This in turn increases the storage time that results in a longer turn-off time, thereby reducing the switching speed. To overcome this problem, a non-saturating switch is discussed.