1150 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



JO 4 



4 5 6 



INPUT VOLTS 



Fig. 9 — Transmission gate signal output potential versus input signal 

 potential. 



To enable the gate, voltages must be impressed such that 



E2 > RJb 



(20) 



In disabling the gate, either one of the control paths may have to carry 

 the full bias current. If, for example, the bias current were flowing in 

 D2 it would bias that control path positive by an amount R2lb- To over- 

 come this, and keep Vb negative, the requirement is: 

 To disable the gate, voltages must be impressed such that 



El < -Rih 

 E2 < -Rih 



(21) 



These sets of conditions give the magnitudes of the biases which 

 are necesssary to hold the gate either enabled or disabled, and the dif- 

 ference between them is the minimum magnitude of the necessary switch- 

 ing pulse. 



EXPERIMENTAL GATE 



An example may be given, using 400B diodes. The bias was chosen 

 as 5 ma and the load resistance, 2,000 ohms. The control resistances 

 were made small, as is desirable for reasons which will be discussed later. 

 For this gate the output voltage is 10 volts. From (20) and (21) the gate 

 could be enabled by 10 volt positive control pulses and disabled by very 

 small negative control values. A larger than necessary control voltage 

 was put on control 2, 



E2 = 15 volts 



