TRANSISTOR BINARY PULSE REGENERATOR 1065 



I frequency by exciting a high Q filter circuit from the received pulse train. 

 [Short timing pips generated from this wave are used to time the regen- 

 erated output pulses precisely. This procedure is far too involved to be 

 used in a simple repeater. If less precision in timing is acceptable it may 

 be accomplished with a minimum of circuitry by use of a sinusoidal wave 

 derived from the repeater output. This is referred to in this paper as 

 "self timing." 



Self timing prohibits the use of short timing pips derived from the 

 i-egenerator output. In this case most of the timing control would be 

 exercised by the filter circuit and little, if any, by the input signal. The 

 direct use of the sinusoidal output of this filter provides suflficient control 

 by the input signal with only a small penalty due to less precise timing.* 

 Self timing also sets certain requirements on the regenerator. If the tim- 

 ing wave is derived from an independent source it can be added to the 

 signal in such a way as to act as a pedestal, lifting the signal above the 

 tiigger level. In such a circuit neither the signal nor the timing wave 

 alone can trigger the regenerator. If the timing wave is derived from the 

 output it is obvious that the signal alone must be able to trigger the 

 regenerator, since the generation of a timing wave depends upon the sig- 

 nal triggering the regenerator. A timing wave derived by filtering the 

 output of a random pattern of binary pulses will also have a varying 

 amplitude which could cause variations in repeater noise margins. It is 

 apparent then that self timing output cannot be used as a pedestal in a 

 regenerator. All these objections can be overcome by the use of "inverted 

 pedestal" timing. 



Inverted pedestal timing is produced by tying the peaks of the timing 

 wave having the same polarity as the signal pulses to a fixed level by 

 means of a diode. This is illustrated on Fig. 1(f). The timing wave is added 

 to the signal at the input so the sum of the signal, feedback and timing 

 looks somewhat like the wave on Fig. 1(g). The effect of the inverted 

 pedestal timing is to inhibit triggering except in the time interval near 

 the peaks of the timing wave. This permits the signal to trigger the re- 

 generator without a timing wave, yet allows timing control to be exer- 

 cised as the amplitude of the timing wave builds up. With sinusoidal 

 timing, noise often causes the regenerator to trigger either early or late, 

 introducing a phase shift in the regenerated ouput which will be reflected 

 in the timing wave. Since the timing wave is derived from the code pat- 

 tern by a relatively high Q tuned circuit, the phase distortion of the tim- 

 ing wave from a shift of a single pulse will be small. With a random dis- 



* E. D. Sunde, Self-timing Regenerative Repeaters (paper being prepared for 

 publication). 



