%
%?FUNCTION?1.2?:?“cp0101_bandwidth“
%
%?Evaluates?the?bandwidth?of?the?input?‘signal‘?with?sampling?period?‘dt‘
%
%?Bandwidth?is?evaluated?according?to?the?given?‘threshold‘（in?dB）
%?‘BW‘?is?the?bandwidth
%?‘f_high‘?is?the?higher?limit
%?‘f_low‘?is?the?lower?limit
%?調制信號的單邊帶寬是基帶信號帶寬的2倍，要調制到1000Hz正弦波上，f0=1e3
%?Programmed?by?Guerino?Giancola
%
function?[ss_Ef_highf_lowBW]=cp0101_bandwidth（signaldtthreshold）

%?---------------------------------------------------------
%?Step?One?-?Evaluation?of?the?single-sided?ESD（功率譜密度）
%?---------------------------------------------------------
threshold=-3;?????????????????????????????????????%?計算帶寬所需要的閾值為-3dB或-10dB
width=1e-1;
points=500;
f0=0;?????????????????????????????????????????????%?要調制到1000Hz正弦波上，f0=1e3

dt=width/points;
signal=zeros（15*points）;?????????????????????????%?矩陣1到5*points
signal（2*points:3*points-1）=ones（1points）;???????%?signal矩陣從2*points到3*points-1這1000點都為1
mod=cos（2.*pi.*f0.*linspace（15*width5*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））;
%?------------------------------------------------
%?Step?Two?-?Evaluation?of?the?frequency?bandwidth
%?------------------------------------------------
[Epeakindex]=max（ss_E）;
f_peak=index*df;
Eth=Epeak*10^（threshold/10）;
%?iterative?algorithm?for?evaluating?high?and?low?frequencies
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（indeximin）-1）*df;
%?end?of?iterative?algorithm
BW=f_high-f_low;
fprintf（‘\nFrequency?Bandwidth=?%f?[Hz]\nHigh?Frequency=%f?[Hz]\nLow?Frequency=?%f?[Hz]\n‘BWf_highf_low）;
%?-----------------------------
%?Step?Three?-?Graphical?output
%?-----------------------------
figure（2）
frequency=linspace（0fs/2length（ss_E））;
PF=plot（frequencyss_E）;
set（PF‘LineWidth‘[2]）;???????????????????????%?線條寬度為[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）;

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----

?????文件???????2712??2008-09-30?18:35??bandwidth.m

-----------?---------??----------?-----??----

?????????????????2712????????????????????1