330 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1954 



The fir'st portion offers a new approach to the everpresent problem 

 of imperfect reactive elements. The second portion discusses a method 

 of combining resistance and capacitance with transistors to produce 

 characteristics conv^entionally realized by inductance and capacitance. 

 The third portion proposes a technicjue for obtaining any specified 

 delay characteristic with a two terminal active structure. The fourth 

 portion considers means of using a transistor to transform passive ele- 

 ments of ordinary size into passive elements of greatly reduced size. 



I. REDUCTION OF DISSIPATION 



For simplicity in the treatment of network problems it is frec^uently 

 assumed that purely reactive elements will be used. In many cases this 

 approximation is satisfactory; other times it is worthless, and a more 

 reaUstic analysis must be made. In this latter case one possibility is to 

 nullify the unwanted dissipation by means of a bridge balance. This 

 will entail the acceptance of some flat loss. Another possibility is to 

 insert active elements within the network in order to supply just enough 

 energy to offset the inherent dissipation of the elements. This second 

 approach, until now relatively unexplored, is being tried with promising 

 results. To avoid introducing new terminology the discussion will em- 

 ploy the concept of negative resistance which has been studied with 

 interest by many investigators."" 



Negative Resistance 



Negative resistance is a misleadingly simple name applied to a com- 

 plex phenomenon. The term implies behavior in some opposite sense 

 to that of an ordinary positive resistance. This is true only for a limited 

 range of frequencies and signal levels. As generally used negati\'e re- 

 sistance refers to a two terminal active network or electronic device in 

 which the voltage-current ratio has a negative real part and negligible 

 imaginary part. 



Table I — Negative Resistance 



Parameter 



Independent variable 



Shunt Type 



Series Type 



Current controlled 



. Voltage controlled 



Required external imped- ' Short circuit stable | Open circuit stable 



ance I 



Increased magnitude of \ Decreased magnitude of 



Rn i Rn 

 Parallel capacitance Series inductance 



Effect of internal gain re- 

 duction 

 Associated reactance 



