340 



THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1951 



45.0 



42.5 



40.0 



37.5 



35.0 



32.5 



30.0 

 10 

 _l 

 HI 



5 27.5 

 O 



°25.0 



z 



1^ ^-^ ^ 

 if) 22.5 

 O 



_i 



g20.0 



H 



a: 



Lij 17.5 



CO 



z 



15.0 



12.5 



10.0 



7.5 



5.0 



8.5 



9.0 9.5 10.0 10.5 11.0 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 8 — Resistance compensation of multi -section filter. 



Series Negative Resistance 



For satisfactory performance in many applications a series resonant 

 circuit should approach zero impedance at the resonant frequency. To 

 reduce the residual dissipation in an ordinary tuned circuit a series 

 negative resistance, consisting of two transistors, can be used. This 

 technique is illustrated in Fig. 11 which shows how a purely reactive 

 shunt branch can be achieved in either an /??-derivcd low pass filter or 

 a confluent band elimination filter. 



