Finding Zero Crossing of Signal

Hello Everyone..

I am sharing the code for which i need to find zero crossing. Though i tried aloy but ould not fix it. Its all working but i need to find the Zero crossing points for signal DA3 in it.

Thanks in advance

Rf = 40e3; Cf = 680e-15;
R2 = 16e3;
R1 = 16e3;
wu = 1 / ((R1 * Rf / (R1 + Rf)) * Cf);
R1da1=1.35e3/2;      %CHANGE FROM PAPER e3/2
R2da1=6.26e3/2;
fda1lp=150e6;%changed from 6 to 5
tau1da1=1/(2*pi*fda1lp);
%%% DA2 Parameters %%% %%%% %%% %%% %%% %%% %%% %%% %%% %%% %%% %%% %%% %%%
R1da2=2.43e3/2;
R2da2=6.26e3/2;
C1da2=84e-12;
%%% DA3 Parameters %%% %%%% %%% %%% %%% %%% %%% %%% %%% %%% %%% %%% %%% %%%
R1da3=2.45e3/2;
R2da3=9.77e3/2;
C1da3=92e-12;
T = 30 / wu;
N = 100;
time = 1: 1: N;
time=T*time/N;
Q = 5e-15;  
QTIME = 4e-9; % Max 11ns
I= Q / QTIME;
to1=1e-9;
to2=to1+QTIME;
syms s;
X1s = (exp (-s * to1)) * 1 / s- (exp (-s * to2)) * (1 / s);
I = Q / QTIME; 
ip = I * X1s;
%%%%%%%%%%%%%%%%%%%%%%%%% Time Domain DA1-DA3 %%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%
syms gda1 t1da1 ;
tf_da1 = gda1 / (1 + s * t1da1);
tf = subs (tf_da1, {gda1, t1da1}, {R2da1 / R1da1, tau1da1});
pretty (tf);
%%%%% DA2 Transfer Function %%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%
syms r1da2 r2da2 c1da2;
tf_da2=(r2da2/r1da2)*(1+s*c1da2*2*r1da2)/(1+s*c1da2*r1da2);
tf_da2=tf_da2./(1+s/(2*pi*150e6));
tf2=subs(tf_da2,{r1da2,r2da2,c1da2},{R1da2,R2da2,C1da2});
pretty(tf2);
syms r1da3 r2da3 c1da3;
tf_da3=s*c1da3*r2da3/(1+s*c1da3*r1da3);
tf_da3=0.1+tf_da3./(1+s/(2*pi*150e6));
tf3=subs(tf_da3,{r1da3,r2da3,c1da3},{R1da3,R2da3,C1da3});
pretty(tf3);
%%%%%%%%%%% Time Domain DA1 %%%%%%%%%%%
syms t ;
da1 = ip * tf;
DA11 = ilaplace (da1);
da1t = subs (DA11, {t}, {time});
%%%%%%%%%%% Time Domain DA2 %%%%%%%%%%%
da2 = da1 * tf2;
da2s = ilaplace (da2);
da2t = subs (da2s, {t}, {time});
%%%%%%%%%%% Time Domain DA3 %%%%%%%%%%%
da3 = da2 * tf3;
da3s = ilaplace (da3);
da3t = subs (da3s, {t}, {time});  % zerocrossing for this signal
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%
close all
figure;
 
plot (time * 1e9, da3t, '-k' , 'LineWidth' , 2);
xlabel ( 'Time - [ns]' ); ylabel ( 'Amplitude - [V]' );
title ( 'DA Transient Output' );
hold on
grid on
legend ( 'DA1' , 'DA2' , 'DA3' );

[Walter Roberson]

Is this a different question than https://www.mathworks.com/matlabcentral/answers/517164-zero-crossing-of-signal ?

[Star Strider]

Unrecognized function or variable 's'.

Error in 
x1s=(exp(-s*to1))*1/s-(exp(-s*to2))*(1/s);

That occurs in the 15th line.

I have been doing my best to help you since you began posting this problem. I will stop if you want to post a different problem.

[Syed Adeel]

Corrected now. It works

Answer 1

[Star Strider]

The end of your code now becomes:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%
close all
figure;

zci = @(v) find(v(:).*circshift(v(:), [1 0]) <= 0);                    % Returns Approximate Zero-Crossing Indices Of Argument Vector
da3td = double(da3t);
idx = zci(da3td);
if da3td(1) * da3td(end) < 0
    idx = idx(2:end);
end

for k = 1:numel(idx)
    t_exact(k) = interp1(da3td(idx(k))+[-1 +1]*1E-5, time(idx(k))*1E9+[-1 +1], 0);
end

plot (time * 1e9, da3t, '-k' , 'LineWidth' , 2);
hold on
plot(time(idx)*1E9, da3td(idx), 'r+') 
hold off
xlabel ( 'Time - [ns]' ); ylabel ( 'Amplitude - [V]' );
title ( 'DA Transient Output' );
hold on
grid on
legend ( 'DA1' , 'DA2' , 'DA3' );
text(t_exact, 0, sprintf('\\downarrow time = %.4f',t_exact), 'HorizontalAlignment','left', 'VerticalAlignment','bottom')

You can eliminate plotting the red ‘+’ if you want.

.