TRIGGERED PULSE GENERATORS 



time constant will then control the duration, and the integrator time constant 

 the slope {Figure 16.19). More often the requirement is to vary the duration 

 whilst maintaining the amplitude. This can be done with the above arrange- 

 ment operating the two controls together, but this is inconvenient and can 

 be avoided by the use of one of the special circuits which follow. 



Eccles-Jordan control 



This circuit {Figure 16.20) appears to be due to Dickinson^. Normally K^ 

 is conducting and V^ cut off. V-^ anode potential is therefore low and the 

 values of the potential divider resistances R^ and R^, in conjunction with the 

 negative supply, are such that V^ anode current is just cut off by the suppressor. 



HT + 



Upon the arrival of a negative trigger pulse the Eccles-Jordan circuit 

 'turns over' and F^ anode goes positive, lifting the suppressor bias on V^ 

 and allowing the Miller run-down to begin. This proceeds until V^ anode 

 reaches a point at which the diode conducts, making V^ grid negative and 

 returning the Eccles-Jordan circuit to the original state. Anode current in 

 F3 is then cut off once more by the suppressor and the flyback occurs. The 

 amplitude of the output is clearly independent of the rate of Miller run- 

 down. 



Sanatron 



In this circuit^ {Figure 16.21) the Miller valve is controlled by a single 

 pentode. V^ is normally conducting hard and V^ anode potential is low; 

 Ri and R2 and the negative supply are arranged so that anode current in 

 Fg is just cut off by V^ suppressor. 



The trigger pulse cuts off F^ on its suppressor, allowing V^ anode to go 

 positive and removing the bias on Fg suppressor. Miller run-down begins, 

 generating via C an approximately constant negative potential across 7?'*, 

 so that Fi remains cut off by its control grid. This state of affairs persists 

 until the run-down begins to slow, and the negative bias, holding F^ cut off, 

 begins to fall. F^ then conducts once more, switching off anode current in 

 V2 and initiating the flyback. 



The circuit will give a constant amplitude of output provided C'R' and 



* Because iR' = C'(dldt){Va), which is constant during the run-down. 



244 



