TRANSISTORS liN SWncillXG CIRCUITS 



J213 



regions, separated by Region II, a region oi negative slope, indicating 

 the possibility of instability. In this particular case, Region I has high 

 lesistance and Region III very low resistance. 



An evaluation of the emitter or input characteristic leads to similar 

 lesults, using the circuit of Fig. 4. Rh has been added here also and Re 

 taken as 2ero. The general pattern is again present. Region I has high, 

 positive resistance; Region Tl, negative resistance; and Region III very 

 low, positive resistance. 



BIASES AXD LOAD LINES — BISTABLE OPERATION 



The negative resistances of Figs. 3 and 4 are both of the so-called 

 open-circuit stable type. If loads are applied to the circuit terminals of 

 Fig. 2 which are larger in magnitude than the negative resistances, the 

 circuits will be stable; that is, there will be single operating points. 

 This is shown in Fig. 4 by the dashed load lines marked, Rt , Rt , Rt . 

 A load resistance smaller in magnitude than the negative resistance 

 may intersect the characteristic in three positions as shown by the 

 load line Re . 



The load line R^ can be made to have single or multiple intei'sections 

 l)y biasing properly as shown in Fig. 5, where the three possibilities are 

 shown as Re , Re , R'i ■ Single or multiple intersections result in ac- 

 cordance with the choice of emitter bias, F„ , as shown. It can be shown 



Fig. 4 — Idealized emitter large-signal negative resistance characteristic. 



