TRANSISTORS IV S\\ ri'( 11 1 N'(; ('[KCriTS 



1 209 



Life reliability and expectancy :ii'c diniciili lo dclci-iniiic due to the 

 relative infancy of transistors, the dcliiiitc rmitciicss of time, tiic many 

 variables involved and the I'ate of development ))r()j>;ress. Average life 

 is presently estimated to be in excess of 70, 01)0 hours. Ijfe is a function 

 of the operating conditions and may l)e materially reduced accordingly. 



Transistors also have limitations. Xoise at present is high for point- 

 contact types as compared to electi-on tubes; input impedances are low, 

 which may be either advantageous or disadvantageous; power output 

 may be limited; frequency response is relatively low; circuit instability 

 may cause design difficulties; and the devices are sensitive to tempera- 

 ture changes. There is also an absence of a long practical experience 

 with a consequent art background in both devices and circuits. 



A comprehensive review of transistor properties is given in the paper 

 l)y J. A. Morton.3 



While it is difficult to define the switching field, it is no less difficult 

 to discuss circuit and device properties on a general basis. This is related 

 to the non-linear nature of the circuits and devices in distinction to the 

 virtually classical linear small-signal field. The lack of a classical method 

 of analysis is a serious handicap in the synthesis of contemporary circuits 

 and de'^dces. When new devices, as the transistor, are to be considered, 



Fig. 1 — A miuKUunj ;\\ 



i^pe transistor (M1689). 



' J. A. Morton, "Present Status of Transistor Development", Bell System 

 Tech. J., 31, pp. 411-442, May, 1952. 



