TRANSISTOR PULSE REGENERATIVE AMPLIFIERS 



1103 



The principal factor that influences the choice of the output-feedback 

 connection is the nature of the output load of the ampHfier. In the 

 majority of computer and switching systems the ampUfier must drive a 

 multiplicity of paralleled load circuits, as indicated in Fig. 10 (a). The 

 input characteristic of each load circuit is assumed to be of the threshold 

 type, like the AND-type input characteristic of Fig. 7 (c), which results 

 in the amplifier load characteristic of Fig. 10 (b). During the initial por- 

 tion of the rise time of the output pulse the incremental impedance 

 is almost zero and during the remainder of the pulse duration it is rela- 

 tively large. Due to the voltage threshold nature of the load, the ampli- 

 fier load variations are current variations at a constant voltage. The 

 minimum current is encountered in the system position where the ampli- 

 fier drives the smallest number of logic circuits, often a single logic cir- 

 cuit; the maximum current is hmited by the maximum output power of 

 the amplifier. Although a desirable ratio of maximum to minimum cur- 

 rent may be as high as 20 : 1 , the amplifier is expected to exhibit optimum 

 performance at any load current within this range. 



The shunt connection of the output and feedback circuits is illus- 

 trated in Fig. 11.12 Windings l:wi constitute the feedback couphng and 

 1 : Hi the output coupling. The two circuits shunt each other in the sense 

 that the ratio of the feedback to the output current is determined by the 

 ratio of the impedance of these circuits as modified by the turns ratio 

 of the transformer. 



INPUT TRIGGER CIRCUIT 



-TL 



OUTPUT 



SINE WAVE 

 TIMING VOLTAGE 



SYNCHRONIZING CIRCUIT 



OUTPUT 

 COUPLING CIRCUIT 



Fig. 11 — Shunt connection of output and feedback. 



