1104 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



There are two limitations associated with this output-feedback con- 

 nection. In the first place there is the possibility of insufficient output 

 voltage, slow rise time, or complete faihu'e of regeneration. This is 

 caused b}' the shunt effect of the output load which places an almost zero 

 initial incremental impedance across the feedback path. In order to 

 overcome this limitation a current switch (R5 and DO in Fig. 11) is used 

 to obtain a low initial feedback impedance and the output diode (D4) 

 is reverse biased so that the initial load impedance is large. The price 

 paid is the undesirable power dissipation in the current switch. ]\Iore- 

 over, stray capacity across the output terminal or a load current that 

 exceeds the design value may still result in a long rise time, low output 

 voltage, or regeneration failure. 



The series connection of the output and feedback circuits is shown in 

 Fig. 12. In this connection the output load is in series with the feedback 

 loop. Thus, the transistor output current, feedback current, and output 

 load current are all proportional to each other. This situation assures 

 regeneration regardless of output load current variations. 



The regeneration cycle of the series type amplifier is as follows. In 

 the quiescent state diode D2 is reverse biased by VI to prevent false 

 triggering. After the arrival of an input signal, the timing signal voltage 

 goes positive and steers the trigger current into the transistor. Xo 



TRIGGER 

 CURRENT 



R1 



INPUT TRIGGER 

 CIRCUIT 



FEEDBACK CIRCUIT 



D2 



1^ 



Dt 



TIMING 

 SIGNAL 



SYNCHRONIZING 

 CIRCUIT 



Lp 



TRANSISTOR 



D6 



I 

 I 

 I 

 I 



V4 



»l t 



_rL 



OUTPUT 



I I OUTPUT COUPLING 



Fig. 12 — Series connection of output and feedback. 



