GC_ET_AP_Ckt_B.html

2021-01-13   21:58:32

First, some Electrical Theory from common Electrical Enginering textbooks :

"The AllPass filter has frequency responses which must be zero at w=0 and at w=pi."

In all researched texts, the traditional academic texts specify
that AllPass filters CanNot be used for Low-Pass or High-Pass functions ,
nor for Band-Pass functions.

*** However, the author has developed working Dual-Notch Band-Pass circuits
*** which utilize the AllPass Filter in both LoPass and HiPass configurations
*** to perform the BandPass function,
*** and to produce Dual-Notches around f(0) .

*** Summarized below :



Developmental Simple Version of this project

*******   Experimental Target  :
*******   Reduce Number of MFB filter stages required to Align Signal Phases
*******       in order to support Dual-Notch Generation around f(0)
*******   Original Target was to attach the AFX Dual-Notch Differential technique.
*******   However,
*******      we found that our circuit could produce Dual-Notch Band-Pass Signals
                    ad hoc !
*******   Therefore,
*******     the Target was changed to investigate the quality of the new WaveForms. 

*** Right-Click Schematics and Plots for larger image ***

*******  Simple Developmental ckt , proof of concept.

*******  24 AllPass stages designed as  12 LP and 12 HP 
*** an error was inserted in the tuned f(LowPass)
*** and un-expected results were observed. 


### Presented below is:

### AllPass Schematic :  UnBalanced Lo-Pass_parallel_Hi-Pass  and  Combined.
###   1 AllPass Low Pass   is tuned to 7 Hz.
### 10 AllPass High Pass are tuned to 700 Hz.

 ### The AP LO is Combined with the AP HI to produce the AllPass Output signal.

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### Below is the Revised and Simplified All-Pass Schematic
### with ONE APF-Lo=7Hz and  TEN APF-Hi=700Hz.


*** Below is the Revised All-Pass Bode Plot for  All-Pass V(out)
*** showing Notches where w=0 or w=pi.
*** The tick indicates f(700).
*** The two adjacent notches [ f(515) and f(900) ]
***    are exactly useful for building a Working Band-Pass Filter.




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*** In this All-Pass  project,
***    the authors accidentally tuned all the All-Pass-filter stages
to f(0) = 7 Hz  and to f(0) = 700 Hz ,
***    which accentuates the "w" notches at each "0" and each "pi" point in the spectrum.
*
*** Observing the useful Bode plots, we explored further, along this Accidental Path.
*** In the fully developed #1 Working Circuit,
***    we preceeded and followed the All-Pass array
***    with Multi-FeedBack Band-Pass OpAmp Active Filters
***    to reduce unwanted side-band signals ( away from f(0) = 700 Hz ).
*** The authors explored the "UnBalanced" ([1F & 10F] and  [7 Hz & 700 Hz] ) approach.
***    The All-Pass-Lo is tuned to 6.92 Hz (7Hz).
***    The All-Pass-Hi is tuned to 692 Hz (700Hz).
***    These frequencies were chosen to utilize standard resistor values.

*** Presented above is a Simplified Proof-of-Concept All-Pass Filter
*** showing the array of notches, 
*** two of which are +/- f(700) and exactly useful.

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