16 



TRIGGERED PULSE GENERATORS 



Triggered pulse generators are circuits which are inactive until the arrival 

 of a brief control or 'trigger' pulse, when they go through a cycle of activity 

 during which a special waveform is generated and at the end of which they 

 are 're-cocked' and ready to repeat the performance upon the arrival of 



Trfgger_ 



Trigger_ 



Output 



Output 



Figure 16.1 



./4 



Figure 16.2 



another pulse. The most important waveforms required of circuits of this 

 kind are a single square wave (Figure 16.1) or a single triangular wave 

 (Figure 16.2). 



SINGLE SQUARE WAVE GENERATORS 



The cathode coupled flip-flop 



This circuit has the appearance of Figure 16.3, from which it is evident that 

 it is closely related to the cathode coupled multi-vibrator; in fact it may be 

 regarded as a multi-vibrator in which Kg grid has been given so much positive 



HT* 



Figure 16.3 



bias that in the absence of an outside stimulus oscillation is prevented. In 

 the 'cocked' condition Fg is conducting heavily because of the large positive 

 bias on Fg grid, and a considerable current flows down Rj^, making the 

 common cathode sufficiently positive to cut off V^. 



The circuit is 'fired' by applying to F^ grid a short positive pulse which 

 allows Kj to conduct. V^ anode potential then falls, driving V^ grid negative 



235 



