532 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



hard plastic bead. A finished transistor is shown in the photograph of Fig. 2. 

 It should be pointed out that Fig. 1 is not drawn to scale and that the />-layer 

 may be less than a thousandth of an inch thick. 



Static Characteristics 



A great deal of information about the low frequency performance of a 

 transistor can be obtained from a set of static characteristics such as those 

 shown in Fig. 4. Curves of this sort, are obtained simply by connecting suit- 



Fig. 2 — A beaded n-p-n transistor. 



EMITTER — *► /^ X -* — COLLECTOR 



Fig. 3 — The symbol for a p-type transistor on which the convention of signs for cur- 

 rents and voltages is indicated, 



able current sources to the emitter and collector circuits of the transistor 

 and measuring the resulting voltages. The currents are called positive 

 when they flow into the emitter and collector as shown and the voltages are 

 called positive when they have the signs shown in Fig. 3. 



Let us first examine these curves with an eye to finding out what kind of 

 voltage and current supplies are needed to bias the transistor into the range 

 in which it can amplify. To make this easy, that part of the characteristics 

 which lies within the normal operating range has been shown as solid lines 

 and that part of the characteristics corresponding to cutoff has been shown 

 as dotted lines. 



