1088 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



Fig. 2. In the following sections the relation between each of the above 

 functional features and amplifier performance is discussed, various circuit 

 configurations to achieve each function are investigated, and the inter- 

 actions between the functional circuits are examined. The design of any 

 particular ampUfier then consists of a suitable selection of a transistor 

 and functional circuits to achieve the desired amplifier performance. 



2. TRANSISTOR PROPERTIES 



In a regenerative amplifier the transistor operates as a switch with 

 power gain. The "on" and "off" state usually are characterized, re- 

 spectively, by high and low collector current levels, and changes of state 

 are initiated by applied control signals. The performance items of interest 

 are the power dissipation in the two states, the speed with which the 

 transistor changes state, the amount of power gain available, and the 

 attainable margins against false operation. The transistor parameters 

 related to these items, as discussed below, are listed in Table I with 

 typical values for several classes of transistors. Desirable and satisfactory 

 values have been indicated in italics. 



The power dissipated in a transistor in the "off" state is proportional 

 to Ico , the collector current with the emitter open circuited, and to the 

 collector supply voltage. This is wasted power and, since the minimum 

 collector supply voltage usually is dictated by other considerations, a 

 low Ico current is desirable to reduce standby power. Point contact units 

 are relatively poor in this respect. In junction imits the 7,0 power is 

 almost negligible compared to other circuit standby power. 



The power dissipated in a transistor in the "on" state is proportional 

 to the saturation voltage between the collector and the common terminal. 



Table I — Transistor Switching Properties 



Switching Features 



Ico at Vc = lOv 



Collector to emitter satura- 

 tion voltage at Ic = 10 ma. 



fa cut-off 



Base resistance 



Collector capacitance at 

 Vo = lOV 



Collector breakdown volt- 

 age 



Punch through voltage 



llmitter breakdown voltage 



Ratio of alpha at le = 10 /xa 

 to alpha at lo = 1 ma . . . 



Point Contact 



Transistors 



(Low Resistivity Ge) 



1500 Ma 



0.8 V 

 15 VIC 

 SO oJmis 



0.5 UUF 



40 V 

 no punch through 

 40 V 



3 



Junction Triode Transistors 



Ge Grown 



5 fxa 



0.5 V 

 2 mc 

 500 ohms 



10 UUF 



100 V 

 100 V 

 5 V 



0.8 



Ge Alloy 



5fxa 



0.05 V 

 4 mc 

 100 ohms 



20 UUF 



35 V 

 35 V 

 35 V 



0.8 



Si Grown 



0.01 iM 

 4 V 



4 mc 

 500 ohms 



10 UUF 



100 V 

 100 V 

 1 V 



0.6 



