1148 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



diodes are involved and they do not change as rapidly with current 

 in milliamperes as the reverse conductance does with volts. Fig. 9 shows 

 the actual input output relation for the signal. It is linear over 80 to 90 

 per cent of the 5-volt range and then limits as expected. 



The discrimination was not measured. It computes to better than 

 60-db voltage loss and discrimination of that order of magnitude has 

 been measured in gates of this type. 



SWITCHING GATE C 



A form of gate which is useful for pulse systems, since it lacks the 

 pedestal, is shown on Fig. 10. This is, of course, basically the same con- 

 figuration as that shown on Fig. 5, but it is operated quite differently, 

 with pulses or dc potentials applied to the two control inputs and an 

 output obtained by switching the bias current from flowing in a control 

 path to flowing in the load. More specifically, if both Ei and E2 are suf- 

 ficiently negative, diodes Di and D2 are both conducting, Vb is negative, 

 and Dz is non-conducting. Thus practically all the bias current h flows 

 in Di and Z>2, and V2 is zero or slightly negative. If one of the control 

 voltages is increased until its diode cuts off, the bias current can still 

 flow in the other control path and the change in the output voltage is 

 extremely small. If both the control voltages are increased until the 

 two control diodes are cut off, then Vb becomes positive, Dz conducts 

 and practically the entire bias current flows in the load, producing an 

 output voltage 



The above operation gives a two control and gate with no pedestal 



2.4 



2.0 



1.6 



0.4 



Fig. 7 — TranHmisHion gate output (pedestal) potential versus gating control 

 potential . 



