952 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



2 5 -4 2 5-3 



DC BIAS CURRENT IN AMPERES 



Fig. 2 — The short-circuit noise current from a point contact or junction diode 

 generally increases with dc bias current. 



A second characteristic feature of noise in all semiconductor devices 

 is that it is current dependent. In the absence of biasing current only- 

 Johnson noise is observed. When biasing current is present the noise 

 power may be as much as three or four orders of magnitude above 

 Johnson noise. As a general thing the noise increases as the bias is in- 

 creased, although some minor exceptions to this rule are noted, usually 

 at bias values where the slope of the current-voltage curve is changing 

 rapidly. 



To illustrate the bias-dependent behavior, the noise properties of 

 some germanium diodes of various types are shown in Fig. 2. The short 

 circuit noise current in a 1-cycle band at 1000 cycles is plotted as a func- 

 tion of dc bias current, some of the data being for forward bias, but most 

 for reverse bias. Several curves are shown for each type of unit, and 



