## Copyright (C) 2018 Jens Ahrensfeld
## 
## This program is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or
## (at your option) any later version.
## 
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
## 
## You should have received a copy of the GNU General Public License
## along with this program.  If not, see <http://www.gnu.org/licenses/>.

## -*- texinfo -*- 
## @deftypefn {Function File} {@var{retval} =} sallenkey_eval (@var{input1}, @var{input2})
##
## @seealso{}
## @end deftypefn

## Author: Jens Ahrensfeld <ahrensfeld@w2ess001vm>
## Created: 2018-05-28

function sallenkey_eval (f_cut_Hz, Q)

w_cut = 2*pi*f_cut_Hz;

m = 1.0;
n = Q*(m*m + 1)/m;

R = 1.0e+3;
C = 1/(R*w_cut)

R1 = m*R
R2 = R/m

C1 = n*C
C2 = C/n


w0 = 0.1;
w1 = 2*pi*1e+6;
w_step = 10;

s = j*(w0:w_step:w1);

H_s = 1./(1 + C2*(R1 + R2)*s + C1*C2*R1*R2*s.^2);

semilogx(abs(s)/(2*pi), abs(H_s)); grid; xlabel('f/Hz'); ylabel('|H(j*2*pi*f)|')




endfunction