324 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 



data displayed in Fig. 20 which gives the volt-ampere characteristics of a 

 silicon diode measured at 20°C and 40°C. Throughout this temperature 

 range, the diode voltage corresponding to the critical resistance of 

 30,000 ohms changes by about 30 millivolts. Fortunately, part of this 

 voltage variation with temperature is compensated for by the variation 

 in voltage Vb-e between the base and emitter of the junction transistor. 

 From Fig. 18, 



V, = Vo - Vb-e + Ve 



(27) 



For perfect compensation (Vi independent of temperature), Vb-e should 

 have the same temperature variation as the diode voltage Vd . Experi- 



REFERENCE 

 I LEVEL 



-I ADJUSTMENT i+ 





Fig. 18 — Simplified circuit diagram of voltage comparator. 



Fig. 19 — Equivalent circuit of voltage comparator. 



