------ This All-Pass Experimental project was started in 2019 -----------
*** Purpose :
All-Pass Experiments to reduce number of Resonant BandPass
required for Phase-Alignment

*** Results : Non-Resonant All-Pass stages can produce Notches usable in the Dual-Notch process.
*** Results : More stages are required, and Notches are not as deep as with AFX, but Very Deep Enough.

First, some Electrical Theory from common Electrical Enginering textbooks :

"All-Pass" defined :
"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) .

( "Working Circuits" Page )

*** Working Circuits : (GC_ET_APC_F8AFQ.html) (click)

*** Working Circuits : (GC_ET_AP_Ckt_A.html) (click)

*** Working Circuits : (GC_ET_AP_Ckt_B.html) (click)

( "Developmental Circuits" Section below )

Developmental versions of All-Pass circuits

*** 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.

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Contributors to this project :

Glen Ellis, E.E., Univ Tennessee, Memphis, TN, USA

Mark Sitkowski, E.E., Design Simulation Systems Ltd, Australia

Joseph Puncochar, E.E. ,VŠB-Technical Univ of Ostrava · Czech

Robert Arnold Orban, Master E.E., Stanford Univ, California, USA,
Dr. Barrie Gilbert, Vp-Eng, Ph.D., Analog Devices., Inc. Beaverton, Or, USA.

*******************************************************************************

Below: All Circuits require new Schem to match the Bode plots.
Freq are 7Hz and 700 Hz. Resistors need correction.
### Lo=7Hz (1M Ohm) Hi=700Hz (10 K Ohm).
.

*** Simple All-Pass Dual-Notch Circuit , Voltage-Mixer Final
******* Simple Developmental ckt , proof of concept.

### 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.

***********************************************************************
### Below is the Revised and Simplified All-Pass Schematic
### One AP Lo-Pass combined with 12 AP Hi-Pass stages.
### Lo=7Hz (1M Ohm) Hi=700Hz (10 K Ohm).

AP24-2F-20F-sum-S-413-2-191210-1200-{medg}.jpg

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

AP24-2F-20F-sum-B--413-1-191210-1115-a700-n505-n960-n36dB-wide.jpg

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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 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" ( 700 Hz and 700 Hz ) approach.
***    The All-Pass-Lo is tuned to 692 Hz.
***    The All-Pass-Hi is tuned to 692 Hz.
***    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.

*********************************************************
*** Below are the Developmental All-Pass Circuits:

*** 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.

### 24 AllPass Schematic : UnBalanced Hi-Pass_parallel_Lo-Pass and Combined.**
### 12 AllPass Low Pass are tuned to 7 Hz w 1M Ohm.
### 12 AllPass High Pass are tuned to 700 Hz w 10K Ohm.
### The AP LO is Combined with the AP HI to produce the AllPass Output signal.

( )

### Below is the Original RAW All-Pass V(out) showing Notches where "w=0" or "w=pi" .
*** this observation lead to further experimental designs.

( )

*************************************************************************************************************************************************
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*** In this #1 project,
***    the authors accidentally tuned all the All-Pass-filter stages to
f(0) = 7 Hz w 1M Ohm
(0) = 700 Hz w 10K Ohm
***    which
*** accentuates the "w" notches at each "0" point
*** accentuates  each "pi" point
*
*** 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 filters
***    to reduce unwanted side-band signals ( away from f(0) = 700 Hz ).
*** The authors explored the "UnBalanced" ( 7 Hz and 700 Hz ) approach.
***    The All-Pass-Lo is tuned to 6.20 Hz.
***    The All-Pass-Hi is tuned to 692 Hz.
***    These frequencies were chosen to utilize standard resistor values.
*** Further #2 development will be done using the"UnBalanced" design
***    with f(0) at 650 Hz and 750 Hz to observe the effect.

*** DUAL-NOTCH Band-Pass schematic :

*** Un-Balanced design : LO=007 Hz and HI=700 Hz, Hi/Lo Voltge-Mixed ,

*** Band-Pass aligned with w=0 and w=pi.
*** DUAL-NOTCHES down to -50 dB .

*** DUAL-NOTCH Bode Plot, Scale : 700mV = -3dB ; 500mV = -6dB.

*** Bode of NO-Notch ; Scale : 700mV = -3dB ; 500mV = -6dB

------ This All-Pass Experimental project was started in 2019 -----------*** Purpose : All-Pass Experiments to reduce number of Resonant BandPass required for Phase-Alignment