1144 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



maximum current which the signal generator could put into the same 

 point when that point is grounded. If the control and bias current sum 

 is larger, the current in the input diode cannot reverse. 



The inequality (10) is to insure that the output diode remains con- 

 ducting. Substituting the value of Vi in it gives: 



h + GE, > 



-G 



Go + G 



(12) 



The only way that the output diode could be cut off (with positive bias 

 and control) is by a large negative signal current. The above inequality 

 requires : 



To hold the output diode conducting, the sum of bias and control 

 generator currents must be greater in magnitude than the maximum 

 negative signal current that the signal generator could put into the 

 midpoint when the midpoint is grounded. 



A zero potential on the midpoint is the boundary condition between 

 the diodes being conducting or non-conducting. The two inequalities 

 together compare the currents that the generators can put into the 

 grounded midpoint. They require: The sum of bias and control generator 

 currents should exceed in magnitude the maximum current of either 

 polarity, that the signal generator can put into the grounded midpoint. 



There remains the inequality (9) which is necessary if the control 

 diode is to remain non-conducting. This gives: 



Gh 



Go + G 



+ h <2 



GoG 

 Go+G 



E. 



(13) 



This compares the same bias and signal generator currents with the 

 current which would flow in the input and the output circuit if Vi 

 were replaced by Eb. If the inequality is satisfied Vi can never get as 

 large as Et and the control input diode remains cut off. 



lb 



V, 



9 



I 



Fig. 6 — Transmission type diode gate. 



