1142 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



results) can readily be applied to the numerous variants which may be 

 encountered. The first is a form of ''linear" or ''transmission" gate. As 

 previously stated, this gate has one or more control inputs, a signal 

 input, and an output. When the control input enables the gate, a rea- 

 sonably accurate replica of input signal should appear at the output. 

 When the control input disables the gate, transmission of a signal should 

 be effectively suppressed. Fig. 5 shows a form of this gate with a single 

 control. This differs from the gates previously shown in that there is a 

 diode in series with the output. Since this gate has superior discrimina- 

 tion and impedance characteristics, compared with the simpler forms it 

 seemed desirable to analyze it as the typical transmission gate. 



In this circuit, 7o, Go represent the signal generator as a current 

 generator with internal conductance Go. Since the transmission proper- 



Fig. 4 — Combination of inhibited gates into and not gate. 



ties are of major interest, the load has been assumed to have the same 

 conductance as the signal generator. A constant current bias /& is im- 

 pressed' at the midpoint of the gate. The control input voltage is repre- 

 sented by Eh. The internal control generator conductance, which should 

 be large, is assumed to be included in the corresponding diode conduct- 

 ance, for computing purposes. The diodes are assumed to have a large 

 conductance G, or a small conductance g depending on whether they 

 are forward biased or reverse biased. Fig. 5 shows the gate enabled, 

 with the series diodes in the conducting state and the control diode 

 in the reverse bias, or non-conducting condition. If the G and g are inter- 

 changed the gate is in the disabled condition. 



The relative magnitudes of Fo, Fi, V2 evidently determine whether 

 the diodes are biased forward or backward. Their magnitudes are im- 

 mediately obtainable. The equations for the case shown in Fig. 5 are: 



* In ca49e the internal conductance of an actual bias source is not sufficiently 

 small to be neglected, its main effect will be on transmission loss. In computing 

 the loss, the bias conductance may be added to the conductance of the control 

 connection. 



