1294 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



The low-frequencies values of the hybrid ("h") parameters may be 

 calculated from the conductances, etc.. given above, but more direct 

 methods are available and are used. The expressions required for both 

 types of computation are given, however. 



/i2i ^ —ace^ —0.985 



hi2 C^ {gcc/9ee) + hiiU + Mbc 



qw dVc 



h22 ^ ^"^" " ^"^" = gcc[l - aecace] 

 Qee 



g[ = h22 = - [2(1 - ^o) + (1 - To)] ^ = 0.11 mho 



W dVe 



hio^ f- (1 - ace)n 



Qee 



c^ 26 + (0.015)278 ~ 30.5 ohms 



These parameter values are in the range commonly encountered in 

 drawn crystal units of good quality. It is obvious that this unit may be 

 unstable at high temperatures, since the current transmission factor 

 (alpha) is greater than unity at 70°C. The rise in alpha is the result of 

 the very large increase in the hole density in the collector which accom- 

 panies the temperature rise. 



In terms of the conventional tee network of Ve, n, r^ and a, two points 

 are interesting. First, the collector resistance Vc ^^ I//12? ^^^ 9 megohms 

 may seem very high. Actually, the lower values so commonly encountered 

 are primarily the result of high leakage conductance, rather than a large 

 electronic conductance. Second, the tee network base resistance 

 Tb ^^ hi2/h22 ^^ 1000 ohms is nearly four times the high frequency feed- 

 back base resistance of 278 ohms. 



5.3 p-n-p Fused Junction Transistor 



The physical structure assumed for this unit is that of Fig. 2(b). 

 The ring base contact is of particular importance. The material and 

 structure are chosen to facilitate comparison with a specific develop- 

 ment model for which a large amount of data is available. The emitter 

 diameter is 15 mils and the collector diameter 30 mils. The base contact 

 ring diameter is 40 mils. 



