bandwidth1.asv

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%
%FUNTION 1.2:"cp0101_bandwidth"
%
%evaluates the bandwidth of the input 'signal' with sample period 'dt'
%
%bandwidth is evaluated according to the given 'threshold'(in dB)
%'BW'is the bandeidth
%'f_high'is the higher limit
%'f_low'is the lower limit
%
threshold=-3;
width=1e-1;
points=1000;
f0=1e3;
dt=width/points;
signal=zeros(1,5*points);
signal(2*points:3*points-1)=ones(1,points);
mod=cos(2.*pi.*f0.*linspace(1,5*width,5*points));
signal=signal.*mod;
fs=1/dt;
N=length(signal);
T=N*dt;
df=1/T;
X=fft(signal);
X=X/N;
ds_E=abs(X).^2/(df^2);
ss_E=2.*ds_E(1:floor(N/2));
[Epeak,index]=max(ss_E);
f_peak=index*df;
Eth=Epeak*10^(threshold/10);
imax=index;
E0h=ss_E(index);
while (E0h>Eth)&(imax<=(N/2))
    imax=imax+1;
    E0h==ss_E(imax);
end
f_high=(imax-1)*df;
imin=index;
E0l=ss_E(index);
while (E0l>Eth)&(imin>1)&(index>1)
    imin=imin-1;
    E0l=ss_E(imin);
end
f_low=(min(index,imin)-1)*df;
BW=f_high-f_low;
fprintf('\nFrequency Bandwidth= %f [HZ]\nHigh Frequency= %f [HZ]\nLow Frequency= %f [HZ]\n',BW,f_high,f_low);
figure(2)
frequency=linspace(0,fs/2,length(ss_E));
PF=plot(frequency,ss_E);
set(PF,'LineWidth',[2]);
L1=line([f_high f_high],[min(ss_E) max(ss_E)]);
set(L1,'Color',[0 0 0],'LineStyle',':')
L1=line([f_low f_low],[min(ss_E) max(ss_E)]);
set(L1,'Color',[0 0 0],'LineStyle',':')
L1=line([f_low f_high],[Eth Eth]);
set(L1,'LineWidth',[2],'Color','red','LineStyle',':')
axis([0.8*f_low 1.2*f_high -0.1*Epeak 1.2*Epeak]);
AX=gca;
set(AX,'FontSize',12);
T=title('Frequency domain');
set(T,'FontSize',14);
X=xlabel('Frequency [HZ]');
set(X,'FontSize',14);
Y=ylabel('Single-Sided ESD [V^2s/HZ]]');
set(Y,'FontSize',14);