TRANSISTOR PULSE REGENERATIVE AMPLIFIERS 



nil 



The next basic selection is the choice of an appropriate transistor. In 

 this computer it is expected that pulses will occur in only about one 

 third or less of the pulse time slots due to the nature of the digital in- 

 formation. In order to minimize the dc standby power an alloy junction 

 transistor is a logical choice for this application because of the low Ico 

 current. However, even with a junction unit possessing an alpha cut- 

 off frequency of eight megacycles, it is difficult if not impossible to ob- 

 tain acceptable gain and rise time with the desired output load current 

 at a one megacycle repetition rate. If the rise time is improved by in- 

 creasing the trigger current, the gain is decreased. The principal cause 

 of the poor "gain-bandwidth" appears to be the depletion layer capaci- 

 tance.^^ The difficulty can be overcome by selecting a point contact 

 transistor. A particular germanium transistor coded GA-52996* appears 

 to be suitable and has the following pertinent characteristics: 



a. Collector capacitance less than 0.5 uuf, 



b. Alpha cut-off frequency in excess of 80 mc, 



c. Base resistance less than 100 ohms. 



Since the alpha of this unit is greater than 2 at collector currents of 

 the order of 10 ma, the common base connection will yield the greatest 

 current gain. The disadvantage of a point contact unit, of course, is the 

 Ico current. For this reason the amplifier will have to be designed to use 

 the smallest possible collector supply voltage. 



The point contact transistor, due to its high cut-off frequency relative 

 to the amplifier pulse repetition rate and its high alpha at small emitter 



T~L 



INPUT 



I 



-8V 



I 

 I 



+6V 



3 VOLT PEAK 



i I MEGACYCLE 



SINE WAVE 



VOLTAGE 



I-2V 



_rL 



-w- 



OUTPUT 



Fig. 13 — Illustrative design 



* This is a relatively special unit especially suited for high speed switching 

 applications. 



