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1995-02-01
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242 lines
-------------------FILTER.DOC for the program A-FILTER.EXE-------------------
.
A-FILTER will run on machines with 256K, EGA, CGA or Herc monochrome
monitors, and a single floppy. A-FILTER may of course be installed on your
hard disk.
.
This program calculates the resistor and capacitor values for various op-amp
active filters.
.
The filters covered are:
.
1. Low pass, 1st order
2. High pass, 1st order
3. Low pass, 2nd order,equal component value Sallen-Key
4. High pass, 2nd order,equal component value Sallen-Key
5. Low pass, 3rd order,equal component value Sallen-Key
6. High pass, 3rd order,equal component value Sallen-Key
7. Low pass, 4th order,equal component value Sallen-Key
8. High pass, 4th order,equal component value Sallen-Key
.
Calculations will simultaneously include 7 response curves for each filter
(greater than 1st order); Best delay, Compromise, Flattest, Slight dips,
1db dips, 2db dips and 3db dips. These filter configurations can be cascaded
to make bandpass filters.
.
The screens are laid out in a format similar to the illustrations in
"The Active Filter Cookbook" by Don Lancaster.
Sams #21168, Eleventh printing.
.
The screens make reference to the appropriate pages in the book for your
convenience. Refer to these pages and other pages in the book which show the
shape of each curve. Although it is not necessary to have this book to run
A-FILTER, the book provides valuable additional information.
.
REGISTRATION of A-FILTER will bring the most recent disk which will include
many, and possibly all, of the following additional configurations:
.
Low pass, 5th order,equal component value Sallen-Key
High pass, 5th order,equal component value Sallen-Key
Low pass, 6th order,equal component value Sallen-Key
High pass, 6th order,equal component value Sallen-Key
Low and highpass, 2nd order, Infinite gain, Multiple feedback.
Low and highpass, 2nd order, Unity gain Sallen-key, Unity gain
.....State Variable, Variable gain State Variable and Biquad.
Low and highpass, 4th order, Infinite gain, Multiple feedback.
Low and highpass, 6th order, Infinite gain, Multiple feedback.
Low and highpass, 8th order, Infinite gain, Multiple feedback.
2nd order, narrow band bandpass in Multiple feedback, Variable gain
.....State Variable and Biquad configurations.
Several Notch configurations.
.
These configurations were intended to be written into A-FILTER so the
selection screens have provided for them even though they are not available
yet.
.
Some of these additional configurations are covered in "Rapid Practical
Designs of Active Filters" by Johnson and Hilburn; Wiley-Interscience.
Other configurations may or may not be included.
.
REGISTRATION also includes: 8 1/2" x 11" user manual pages for insertion in
your 3 ring binder, support and placement on the update list. The manual
pages are complete with schematics. Also available for EGA users will be a
schematic display of your filter design with a screen dump to dot matrix
or laser printers. Schematics will have all parts labeled.
.
.
The registration fee is $35, payable to:
.
Bill Fitzpatrick
POBox 282
Veneta, OR 97587
.
Phone (503)935-3982
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If you do not wish the most recent version and manual pages, a donation of
$10 is humbly requested.
.
Print out this document, making sure your printer is in the mode required to
accomodate the ASCII characters used.
.
All filter configurations are non-inverting and all except the 1st order
filters have gain. Reduce gain as needed, elsewhere in your circuits.
.
You may, for instance, double the calculated RD value if you also change the
39.2k resistor to 78.4k. The proper ratio of these resistors must be
maintained; their exact value is not important except as it may effect the
offset. High order filters, regardless of the configuration, require
accurate resistance and capacitance values. Since 1% metal film resistors
are available for just pennies each, it would behoove you to use them in
every case.
.
.
FILTER DIAGRAMS & EXAMPLES (all Equal component value Sallen-Key)___________
.
.
.
. ┌──── 10K ────┐
. │ ┌─────────┐ │
. └─┤- │ │
. │ OPAMP ├─┴─────── OUT
. IN ─── RF1────┬─┤+ │
. │ └─────────┘
. C
. │
. ≡
. Fig. 6-14 First order, low pass
.
EXAMPLE:
Take, as an example, the 1st order, low pass filter. When prompted, enter
1000 for Fc and .015 for C. 10,666Ω is shown for RF1. You may stop here and
consider the design finished by using the closest resistor value to 10666Ω
which is 10.7k. Optionally, you may use the <D> key to lower the displayed
RF1 value to 10,497, use a 10.5K resistor and shunt the .015 capacitor with
240pf. Using the <D> key provides the opportunity for greater accuracy in
your critical circuit designs.
.
Hit the <ESC> key and do the next example.
.
.
. ┌──── 10K ────┐
. │ ┌─────────┐ │
. └─┤- │ │
. │ OPAMP ├─┴─────── OUT
. IN ─── C ─────┬─┤+ │
. │ └─────────┘
. RF1
. │
. ≡
.
. Fig. 8-13 First order, high pass
.
.
.
. ┌──39.2k─┬──── RD1 ────┐
. ≡ │ ┌─────────┐ │
. └─┤- │ │
. │ OPAMP ├─┼─────── OUT
. IN ──── RF1 ────┬── RF1 ──┬─┤+ │ │
. │ │ └─────────┘ │
. C C │
. │ │ │
. │ ≡ │
. └───────────────────────┘
.
. Fig. 6-15 Second order, low pass
.
.
.
. ┌──39.2k─┬──── RD1 ────┐
. ≡ │ ┌─────────┐ │
. └─┤- │ │
. │ OPAMP ├─┼─────── OUT
. IN ──── C───────┬── C ────┬─┤+ │ │
. │ │ └─────────┘ │
. RF1 RF1 │
. │ │ │
. │ ≡ │
. └───────────────────────┘
.
. Fig. 8-14 Second order, high pass
.
.
.
. ┌──39.2k─┬──── RD2 ────┐
. ┌──── 10K ────┐ ≡ │ ┌─────────┐ │
. │ ┌─────────┐ │ └─┤- │ │
. └─┤- │ │ │ OPAMP ├─┼─────── OUT
. │ OPAMP ├─┴── RF2─┬── RF2───┬─┤+ │ │
. IN ─── RF1────┬─┤+ │ │ │ └─────────┘ │
. │ └─────────┘ C C │
. C │ │ │
. │ │ ≡ │
. ≡ └───────────────────────┘
.
. Fig. 6-16 Third order, low pass
.
.
.
. ┌──39.2k─┬──── RD2 ────┐
. ┌──── 10K ────┐ ≡ │ ┌─────────┐ │
. │ ┌─────────┐ │ └─┤- │ │
. └─┤- │ │ │ OPAMP ├─┼─────── OUT
. │ OPAMP ├─┴── C ──┬── C ────┬─┤+ │ │
. IN ─── C──────┬─┤+ │ │ │ └─────────┘ │
. │ └─────────┘ RF2 RF2 │
. RF1 │ │ │
. │ │ ≡ │
. ≡ └───────────────────────┘
.
. Fig. 8-15 Third order, high pass
.
.
. ┌──39.2k─┬──── RD2─────┐
. ┌──39.2k─┬──── RD1─────┐ ≡ │ ┌─────────┐ │
. ≡ │ ┌─────────┐ │ └─┤- │ │
. └─┤- │ │ │ OPAMP ├─┼──OUT
. │ OPAMP ├─┼───── RF2─┬── RF2───┬─┤+ │ │
.IN ── RF1─┬── RF1───┬─┤+ │ │ │ │ └─────────┘ │
. │ │ └─────────┘ │ C C │
. C C │ │ │ │
. │ │ │ │ ≡ │
. │ ≡ │ └───────────────────────┘
. └───────────────────────┘
.
. Fig. 6-18 Fourth order, low pass
.
EXAMPLE:
Do a low pass, fourth order, equal value Sallen-Key, with Fc=1000Hz and
C=.015mfd. Again, you may stop here and use the displayed values or
use the <D> key. The Compromise calls for RF1 to be 8800Ω. Use the <D>
until the displayed RF1 is 8660Ω, which is a 1% value. The first section
would then use .015mfd║240pf and 8.66k. Now use the <U> key and return
C to ≈.015. Reduce RF2 to 8253. The second section would use .015mfd║260pf
and 8.25k.
.
.
. ┌──39.2k─┬──── RD2─────┐
. ┌──39.2k─┬──── RD1─────┐ ≡ │ ┌─────────┐ │
. ≡ │ ┌─────────┐ │ └─┤- │ │
. └─┤- │ │ │ OPAMP ├─┼──OUT
. │ OPAMP ├─┼───── C ──┬── C ────┬─┤+ │ │
.IN ── C ──┬── C ────┬─┤+ │ │ │ │ └─────────┘ │
. │ │ └─────────┘ │ RF2 RF2 │
. RF1 RF1 │ │ │ │
. │ │ │ │ ≡ │
. │ ≡ │ └───────────────────────┘
. └───────────────────────┘
. Fig. 8-18 Fourth order, high pass
.
.
.
.
.
I hope you enjoy A-FILTER. Originally written for my own use, it has saved
me many hours of tedious calculations for the devise I designed which uses
90 filters! Pass this version around to your friends and please notify me
of any errors. Additional filter configurations will be added to the latest
version upon request. Do not hesitate to ask. Also, suggestions for
additional routines which you think would make A-FILTER easier to use would
be taken into consideration for inclusion into the program.