THE TRANSISTOR AS A NET-SVOHK ELEMENT 



337 



-30 -28 -26 -16 -14 -12 -10 -8 -6-4-2 2 4 



^ RADIAN FREQUENCY IN HUNDREDS 



Fig. 5 — Effect of reducing dissipation on singularities of confluent band 

 filter. 



the real frequency axis is a function of the amount of dissipation in the 

 elemets. When a vahie of negative resistance corresponding to the 

 p = 1 curve in Fig. 3 is added to the passive filter, the singularities move 

 from positions marked 1 to those marked 2 in Fig. 5. Adding a larger 

 amount of negative resistance corresponding to the p = 1.21 curve in 

 Fig. 3 produces the singularities marked 3. It should be noted that the 

 infinite loss point on the negative sigma axis as well as the two at the 

 origin have not moved. If the dissipation in the shunt branch is reduced 

 by removing the coil and replacing by one having half as much resistance, 

 the singularities change from position one to position four. In this case 

 the infinite loss point on the sigma axis does move. This illustrates that 

 the change in pattern of singularities resulting from use of negative 

 resistance is similar to, but not the same as, that resulting from use of 

 passive inductors having higher values of Q. 



M-Derived Band Pass 



In order to provide a sharp cut-off in a filter use is often made of m- 

 (lerived peak sections. In the configuration shown in Fig. G loss peaks will 

 occur at selected freciuencies al)ove and below the pass band provided 

 the elements are nearly free of dissipation. The closer the attenuation 

 peaks are to the pass band the more nearly free from dissipation the 



