436 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 



tudes as large, as 4-5 volts out of a total collector ^'oltage of 6 volts and 

 rise times as little as 0.01-0.02 microsccoiid. 



By increasing the thermal dissipation limits of junction transistors, 

 the Class A power output has been raised to 2 watts in lal)oratory models. 

 This, however, does not represent an intrinsic upper limit but rather a 

 design objective for a particular application. 



Characteristics suitable for switching are now available in the ]M1698, 

 M1689 and M173-4: point-contact types, as previously described, but 

 this is a continually evolving process and more work certainly remains to 

 be done. At present it is possible to operate telephone relays requiring 

 as much as 50 to 100 ma with Mir)89 and M1698 point-contact tran- 

 sistors. 



New junction-type phototransistors^ represent a marked advance over 

 the earlier point -contact tj^pe.® While their quantum efficiencies are not 

 as high as those of the point-contact types, nevertheless the light/dark 

 current ratios are greatly improved and the collector impedance has been 

 raised 10-100 times thus making possible much greater output voltages 

 for the same light flux. 



SOME SELECTED APPLICATIONS 



Data Transmission Packages 



To determine the feasibility of applying transistors in the form of 

 miniature packaged circuit functions, several of the major system func- 

 tions of a pulse code data transmission system have been studied. This 

 investigation has been undertaken under the auspices of a joint services 

 engineering contract administered by the Signal Corps. 



It was desired that these studies should lead to the feasibility develop- 

 ment of unitized functional packages combining features of miniaturiza- 

 tion, reliability and lower power drain. Accordingly, it was necessary 

 to carry on in an integrated fashion activities in the fields of system, 

 circuit and device development to achieve these ends. In particular, 

 circuit and system means have been developed to perform with tran- 

 sistors the functions of encoding, translation, counting, registering and 

 serial addition. The M1728 junction diode, M1740 junction photocell 

 and Ml 689 bead switching transistor are direct outgrowths of this 

 program and are the devices used in the circuit packages. 



At this point, the major system functions shown in Fig. 27 have been 

 achieved with interchangeable transistors. These major system functions 

 are in turn built up of some seven types of smaller functional packages 

 listed in Fig. 28. The end result of this exploratory development can be 



