486 



BELL SYSTEM TECHNICAL JOURNAL 



about its Internal arrangement and about the impedance of the circuit 

 in which it is to work. 



Regenerative Negative Resistances 

 One of the simplest ways to produce a negative resistance is to inter- 

 connect the input and output terminals of a one-way amplifier. This 

 gives a regenerative arrangement because part of the output energy 

 of the amplifier is fed back into the input circuit. The type of negative 

 resistance obtained depends upon the way in which the interconnection 

 is made. 



Fig. 1 — Ideal one-way amplifier. 



Fig. 1 shows schematically an ideal one-way amplifier for this pur- 

 pose. It has a pair of input terminals 1, 2, and a pair of output ter- 

 minals 3, 4. The impedances between the input and output terminals 

 are pure resistances Ri and R^, respectively. Some mechanism, indi- 

 cated symbolically by the arrow, is provided, which produces an e.m.f. 

 in the output circuit which is proportional to the input current. The 

 nature of this mechanism is not of importance to this discussion except 

 that it is a one-way device. The mutual impedance M is the ratio of 

 the e.m.f. generated in the output circuit to the current in the input 

 circuit. This ratio may be adjusted by suitable means such as a 

 potentiometer but is otherwise constant and includes no phase shift. 

 The internal connections are assumed to be such that when the input 

 terminal 1 is positive to 2 the e.m.f. in the output circuit tends to make 

 terminal 3 positive with respect to 4. 



Series Negative Resistance 

 In Fig. 2 the input and output circuits of the ideal amplifier are 

 connected in series with each other to a source of e.m.f. E and a re- 



Ro 



^8 



Fig. 2 — -One-way amplifier connected as a series negative resistance. 



