310 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 



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FRFOUENCY IN CYCLES PER SECOND 



Fig. 9 — Gain-frequency asymptotes for summing amplifier. 



is generated in the first transistor stage. If the transistor in the first 

 stage has a noise figure less than 10 db at 1,000 cycles per second, then 

 the RMS output noise voltage is less than 0.5 millivolts. 



Fig. 9 shows a plot of the gain-frequency asymptotes for the sum- 

 ming amplifier determined from (13), (14), (15), (17), and (A6) under 

 the assumption that the alphas and alpha-cutoff frequencies of the tran- 

 sistors are 0.985 and 3 mc, respectively. The corner frequencies intro-' 

 duced by the 0.5 microfarad condenser in the interstage network, thel 

 local feedback circuit, and the cutoff of the first and third stages are so 

 located that the current transmission falls off at an initial rate of about' 

 9 db per octave. This slope is joined to the final asymptote of the loop 

 transmission by means of a step-type of transition.^ The transition is 

 provided by 3 rising asymptotes due to the interstage shaping network, 

 and the overall /S circuit. An especially large phase margin is used in order 

 to insure a good transient performance. 



Fig. 10 shows the amplitude and phase of the loop current trans- 

 mission. When the amplitude of the transmission is db, the phase angle 

 is -292°, and when the phase angle is —360°, the amplitude is 27.5 db 



