GC_ET_PFB-bpf.html
2018-01-10
11:05:01

*** Based on circuit design by  Dr. Josef Punchochar  , Research Gate Net 

***  the  Positive-FeedBack Band-Pass Filter,   with single resistor f() control.
Negative FeedBack is Q2 and PFB BandPass V(out) is Q7

Example of circuit modification to handle Positive Boot-Strap Feedback via Multiple-Feedback Band Pass Filter. 
Advantage is : Adjust f(0) via a single resistor R(freqAdj) +/- 500 Hz.  

*** SPICE  circuit, Glen Ellis.
*** Example of circuit modification to handle Positive Boot-Strap Feedback via Multiple-Feedback Band Pass Filter. 
*** Advantage : Adjust f(0) via a single resistor R(freqAdj) +/- 300 Hz. 

*** Balance between Positive & Negative FB
*** else will transform circuit into a Notch Filter  or into an Oscillator.

V(out)   is   NetVout 
f(0) = 700 Hz  
FeedBack Q=2
Effecive  Q=7 
BW=100 Hz  

*** Original NetSigIn ( source signal ) is flat ( green ). 
*** FeedBack   inverted ( blue ) (generated at Q=7)  
*** Overall Response is Q=7  Positive BandPass  ( black ). 
   



Transient Plot : Noise Input and Positive-FeedBack and f(700) filtered V(out) .   Green Noise, Black Positive-FeedBack,  Blue f(700) V(out) .

   Adjust f(0) via a Single Resistor R(freqAdj) +/- 300 Hz. 
   Change f(0) via R6    [ R(freq) ].
   Initially  R(freq) is 6500 Ohm.      Adjust :    Up = lower f(0)   and    Down = higher f(0). 

   In f(0) change,  
   Gain will change as the minor ratio of R(in) / R(freq).
   Q  will change  as  squareroot of delta(f) change.  
   But BW will remain same.   
   ( Author uses this method for adjusting f(0) change of +/- 300 Hz. ) 

*** Demonstrating shifting f(0) via R(freqAdj)


*** Demonstrating circuit to generate bode of shifting f(0) via R(freqAdj)

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