1106 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



circuit to prevent saturation in the transistor,* Because the feedback 

 loop gain, as determined by the alpha of the transistor and the turns 

 ratio 111 , must be greater than unity for regeneration reasons, there will 

 be current flow through D6 during the pulse duration. This current is 

 proportional to the degree of stability. An increase Aiout in the output 

 current causes an increase of 



Az, = ^^^^'-^ (1) 



in the collector current. Therefore, the current in D6 increases by an 

 amount equal to 



AZdb = 



^-1 



\_ni 



riiAiont (5) 



This variation in the degree of stability may be reduced by selecting 

 a/rii close to unity and reducing no . However, since it is desirable to 

 have a/rii much larger than unity for short rise time and since any reduc- 

 tion in n2 increases the Ico standby power, f a compromise is necessary. 



6. SYNCHRONIZING CIRCUITS 



The majority of modern digital data processing systems employ coin- 

 cidence gate circuits to perform the logical functions. In order to insure 

 that digit pulses will coincide at the inputs to the logic circuits, it is con- 

 venient to synchronize the amplifiers. Usually a master oscillator, or 

 "clock," produces the timing signals that are distributed to the ampli- 

 fiers. The function of the synchronizing circuit in the amplifier is to turn 

 on and to turn off the amplifier at predetermined time intervals in re- 

 sponse to the clock signal. 



In a regenerative amplifier there is always a small delay from the time 

 triggering commences until the full output pulse is developed. Then 

 there are variations in the transmission time to other amplifiers. For 

 these reasons the clock signal must lag the input signal to the amplifier 

 in order to maintain control of turn-on and to obtain a uniform pulse 

 length from all amplifiers. Generally the time lag is one-fourth of the 



* In an actual amplifier D6 is not required if the transistor saturation voltage 

 is relatively constant versus collector current and the pulse fall time is not ad- 

 versely affected by minority carrier storage in the transistor. Often the inductive 

 "kick" of the transformers and the regenerative feedback are sufficient to make 

 the minority carrier storage effect negligible. If D6 is used, its reverse recovery 

 time may adversely affect the pulse fall time, thus nullifying its usefulness. 



t The Ico standby power is proportional to V2 , which, for a given output volt- 

 age, is inversely proportional to no . 



