1092 THE BELL SYSTEM TECHNICAL JOUKXAL, SEPTEMBER 1950 



fiers operated in a system for over 17,000 hours with a faihire rate of] 

 slightly less than 0.07 per cent per thousand hours. 



These features, however, are obtained at the expense of relative com-] 

 plex circuitry. This negative resistance type of high speed regenerative 

 amplifier has the following inherent limitations. 



1. The degree of stability in the "on" state depends critically on the 

 collector current. In the example a dummy load must be strapped in 

 when the amplifier drives less than four logic circuits. 



2. A steering diode (D3) and a timing circuit diode (Dl) have critical 

 reverse recovery time^ specifications.* 



3. The requirements on transistor parameters (primarily the dynamic 

 alpha versus emitter current and base resistance characteristics) are 

 relatively critical. 



4. A relatively large amount of synchronizing power is required. 



5. With transformer output coupling (as discussed in Section 5.1) a 

 large amount of the total standby power is absorbed by a circuit required 

 to protect the transistor in case the timing voltage fails (In the example 

 21 milliwatts, or 64 per cent of the standby power, is absorbed by R3.) 



INPUT TRIGGER CIRCUIT 

 !+6V 



FEEDBACK 



CIRCUIT 



TRANSISTOR 



OUTPUTS 



20V 

 PEAK-TO-PEAK 



1 MC 

 SINE WAVE 



SYNCHRONIZING 

 CIRCUIT 



OUTPUT 



COUPLING 



CIRCUIT 



DUMMY 

 LOAD 



Fig. 4 — Negative resistance feedback amplifier. 



varied without causing an operational failure, are an indication of the sensitivity 

 of the amplifier to changes in component values. 



* At lower pulse repetition rates this property may not be critical. 



