864 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



correction. Actually, of course, the above statement is oversimplified 

 but it should be clear that the effective feedback of the regulation system 

 is the (voltage) sum of the feedbacks of the individual regulators. Thus 

 100 regulators each having 20 db of feedback tend to act like a single 

 regulator having 60 db of feedback. The rigorous treatment of these 

 effects will be developed later. 



Fig. 18 shows a block diagram of a regulator in a form intended to 

 indicate the feedback structure. The feedback loop includes a pilot 

 pickoff filter, amplifier and rectifier. This converts the output pilot level 

 into a dc voltage. The ''battery", which is the actual input signal for 

 the circuit, represents the equivalent of the desired pilot output level. 

 The signal applied to the dc amplifier is a dc signal representing the 

 error in pilot level. This dc signal is, in effect, converted back to a pilot 

 level by the action of the regulating network and its modulation of the 

 input pilot level. Thus changes in input pilot level are equivalent to 

 gain changes in the m circuit of the feedback structure and are resisted 

 by feedback action just as in any other feedback ''amplifier". It is also 

 valuable to note the respective m and jS roles played by the various com- 

 ponents since the stability requirements, etc. then become clear. For 



DC AMPLIFIER 



-=- INPUT 



\> 



s 



PILOT 

 INPUT 



REGULATING 

 NETWORK 



DIODE 

 DETECTOR 



PILOT 

 AMPLIFIER 



:<] 



PICK- OFF 

 FILTER 



OUTPUT 



Fig. 18 — Block diagram of regulator showing the feedback structure. 



