📄 qsynth.m
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function [Out1,Out2]=qsynth(Action,In1,In2)
% Dick Benson
% design singly terminated elliptic passive LC low pass filters
% [L,C] = qsynth('getLC');
if nargin ==0
Action = 'init';
end;
if ~strcmp(Action,'init')
Hqsynth_ = get(gcf,'userdata');
end
% handle index definitions
i_f1 = 1;
i_topology = 2;
i_order = 3;
i_synthpb = 4;
i_ripl = 5;
i_ripv = 6;
i_stopl = 7;
i_stopv = 8;
i_ax1 = 9;
i_pl1 = 10;
i_pl2 = 11;
i_fcl = 12;
i_fcv = 13;
i_lv = 14;
i_cv = 15;
i_lcl = 16;
i_testpb = 17;
if strcmp(Action,'init')
color_h; % color definitions
load my_color
qsynth_color=stored_vi_colors;
Hqsynth_(i_f1)= figure('Color',[0 0 0] ,'Name','Qsynth: Singly Terminated Ladder Elliptic Filter',...
'Position',[20 20 640 440],...
'Resize','off',...
'Color',qsynth_color(FIG_BKc,:),...
'NumberTitle','off','visible','on');
% ###### userdata contains vector of handles if desired
Hqsynth_(i_topology)=uicontrol('Style','popup','visible','on',...
'String','RIN=1,RL=inf|RIN=0,RL=1',...
'Position',[10 400 105 20],...
'BackgroundColor',qsynth_color(PUP_BKc,:),...
'ForeGroundColor',qsynth_color(PUP_FRc,:),...
'Value',1,...
'callback','qsynth(''clear'')',...
'HorizontalAlignment','Left');
Hqsynth_(i_order)=uicontrol('Style','popup','visible','on',...
'String','Order:3|Order:5|Order:7|Order:9|Order:11',...
'Position',[10 380 105 20],...
'BackgroundColor',qsynth_color(PUP_BKc,:),...
'ForeGroundColor',qsynth_color(PUP_FRc,:),...
'Value',4,...
'HorizontalAlignment','Left');
Hqsynth_(i_ripl) = uicontrol('Style','text','visible','on',...
'String','Ripple (dB):',...
'Position',[10,355,60,18],...
'BackGroundColor',qsynth_color(LBL_BKc,:),...
'ForeGroundColor',qsynth_color(LBL_FRc,:),...
'HorizontalAlignment','left');
Hqsynth_(i_ripv) = uicontrol('Style','edit','visible','on',...
'Position',[70,355,45,18],...
'String','1',...
'BackgroundColor',qsynth_color(EDT_BKc,:),...
'ForeGroundColor',qsynth_color(EDT_FRc,:),...
'HorizontalAlignment','center',...
'Max',1);
Hqsynth_(i_stopl) = uicontrol('Style','text','visible','on',...
'String','Stop (dB):',...
'Position',[10,330,60,18],...
'BackGroundColor',qsynth_color(LBL_BKc,:),...
'ForeGroundColor',qsynth_color(LBL_FRc,:),...
'HorizontalAlignment','left');
Hqsynth_(i_stopv) = uicontrol('Style','edit','visible','on',...
'Position',[70,330,45,18],...
'String','60',...
'BackgroundColor',qsynth_color(EDT_BKc,:),...
'ForeGroundColor',qsynth_color(EDT_FRc,:),...
'HorizontalAlignment','center',...
'Max',1);
Hqsynth_(i_fcl) = uicontrol('Style','text','visible','on',...
'String','Cutoff (Hz):',...
'Position',[10,305,60,18],...
'BackGroundColor',qsynth_color(LBL_BKc,:),...
'ForeGroundColor',qsynth_color(LBL_FRc,:),...
'HorizontalAlignment','left');
Hqsynth_(i_fcv) = uicontrol('Style','edit','visible','on',...
'Position',[70,305,45,18],...
'String','1.0e6',...
'BackgroundColor',qsynth_color(EDT_BKc,:),...
'ForeGroundColor',qsynth_color(EDT_FRc,:),...
'HorizontalAlignment','center',...
'Max',1);
Hqsynth_(i_lcl) = uicontrol('Style','text','visible','on',...
'String',' L C',...
'Position',[10,280,165,18],...
'BackGroundColor',qsynth_color(LBL_BKc,:),...
'ForeGroundColor',qsynth_color(LBL_FRc,:),...
'HorizontalAlignment','left');
Hqsynth_(i_lv) = uicontrol('Style','edit','visible','on',...
'Position',[10,35,85,240],... % was 80
'String','',...
'BackgroundColor',qsynth_color(EDT_BKc,:),...
'ForeGroundColor',qsynth_color(EDT_FRc,:),...
'HorizontalAlignment','left',...
'Max',14);
Hqsynth_(i_cv) = uicontrol('Style','edit','visible','on',...
'Position',[100,35,85,240],... % was 95,35,80
'String','',...
'BackgroundColor',qsynth_color(EDT_BKc,:),...
'ForeGroundColor',qsynth_color(EDT_FRc,:),...
'HorizontalAlignment','left',...
'Max',14);
Hqsynth_(i_ax1)=axes('Units','pixels','Position',[240,80,370,300],...
'Box','on',...
'visible','on',...
'NextPlot','add',...
'DrawMode','fast',...
'Color',qsynth_color(PLT_BKc,:),...
'TickDir','out',...
'YlimMode','auto',...
'XlimMode','auto',...
'Xcolor',qsynth_color(XY_AXc,:),...
'Ycolor',qsynth_color(XY_AXc,:),...
'FontSize',12);
title('Singly Terminated Elliptic Filter ','color',qsynth_color(XY_AXc,:),'fontsize',9);
xlabel('Frequency in Hz','fontsize',9);
ylabel('Magnitude in dB','fontsize',9)
Hqsynth_(i_pl1) = plot(Hqsynth_(i_ax1),0,0,'clipping','on',...
'Color',qsynth_color(TRA_1c,:),...
'erasemode','xor','visible','on');
Hqsynth_(i_pl2) = plot(Hqsynth_(i_ax1),0,0,'clipping','on',...
'Color',qsynth_color(TRA_2c,:),...
'erasemode','xor','visible','on');
Hqsynth_(i_synthpb) = uicontrol('Style','Pushbutton',...
'Position',[10,10,105,20],...
'String','Synthesize',...
'Callback','qsynth(''synth'');');
Hqsynth_(i_testpb) = uicontrol('Style','Pushbutton',...
'Position',[120,10,105,20],...
'String','Test',...
'Callback','qsynth(''test'');');
set(Hqsynth_(i_f1),'userdata',Hqsynth_);
zoom on
elseif strcmp(Action,'synth')
fmtstr = '%8.5g';
n = get(Hqsynth_(i_order),'value')*2+1; % only odd orders supported
rp = str2num(get(Hqsynth_(i_ripv),'string'));
rs = str2num(get(Hqsynth_(i_stopv),'string'));
wn = 2*pi*str2num(get(Hqsynth_(i_fcv),'string'));
[b,a]=ellip(n,rp,rs,wn,'s');
save lpf_coefs b a
w = 0:(wn/25):10*wn;
h = freqs(b,a,w);
set(Hqsynth_(i_ax1),'Ylim',[-rs-20,5],'Xlim',[0,10*wn/(2*pi)]);
set(Hqsynth_(i_pl1),'xdata',w/(2*pi),'ydata',20*log10(h));
topology = get(Hqsynth_(i_topology),'value');
if topology ==1
% Rin = 1, Rl = inf , Vsource with 1 ohm Z0, no load
% must be odd order
m = b(2:length(b));
zeros = roots(m);
m2 = [];
n2 = [];
for i=1:length(a)
if rem(i,2)
n2=[n2,a(i),0];
else
m2=[m2,a(i),0];
end;
end;
m2=m2(1:(length(m2)-1));
% remove admittance pole @ s=inf
% z=m2/n2 y = n2/m2 yp = n2/m2-c1s
C(1) = n2(1)/m2(1); % shunt capacitor
n2 = n2 - conv(m2,[C(1),0]);
% now it gets tricky ....
for i = 1:(n-1)/2
% need an xmission zero @ w=wx
wx = j*abs(zeros(2*i)); % pick an xmission zero....
% do a partial removal of the impedance pole @ inf
% first evaluate impedance @ w=wx
zmag = polyval(m2,wx)/polyval(n2,wx);
L(2*i) = zmag/wx;
if i==1
n2=n2(3:length(n2));
end;
% this partially removes the pole
m2 = m2-conv(n2,[L(2*i),0]);
% now remaining admittance has a pole at w=wx
% remove it by shunting a series LC
% first must determine L & C values
[q,r1]= deconv(m2,[1 0 abs(wx)^2]); % r should be zero
k = n2(1);
n2p = n2/k;
n2p = n2p(1:length(n2p)-1);
L(2*i+1)=1/(k*(polyval(n2p,wx)/polyval(q,wx)));
C(2*i+1)= 1/(L(2*i+1)*(abs(wx)^2));
% then remove the addmittance.... not obvious!
[n2pp,r2] = deconv(( n2p-q/(k*L(2*i+1)) )*k,[1 0 1/(C(2*i+1)*L(2*i+1))]);
n2 = conv(n2pp,[1 0]);
m2 = q;
end;
L=L';
C=C';
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