SAR—ＡＤＣ　ＳＮＲ仿真问题

时间：10-02 整理：3721RD 点击：

我做的５位的ＳＡＲ—ＡＤＣ，比较器用的是理想模块，其他都是电路，采样率是１ｋ／ｓ，输入１００Ｈｚ的正弦信号，采样１００个点进行ｆｆｔ，最后得出ＳＮＲ＝３２．３ｄＢ，理论值为３１.８ｄＢ，比理论还要高是怎么回事?
ｍａｔｌａｂ代码如下：
clear
load file8.txt%WaveScan保存的波形文件，文件必须以英文开头
A=file8;%将测量数据赋给A，此时A为N×2的数组
x=A(:,1);%将A中的第一列赋值给x，形成时间序列
x=x';%将列向量变成行向量
y=A(:,2);%将A中的第二列赋值给y，形成被测量序列
y=y';%将列向量变成行向量

format long;
%傅立叶变换
y=y-mean(y);%消去直流分量，使频谱更能体现有效信息
fclk=1000;%仪器的采样频率
numpt=length(y);%data.txt中的被测量个数，即采样个数

Doutw=y'.*hanning(numpt);
%Doutw=y';

%Performing the Fast Fourier Transform
Dout_spect=fft(Doutw);

%Recalculate to dB
Dout_dB=20*log10(abs(Dout_spect));

%Display the results in the frequency domain with an FFT plot
figure; %建立图形
maxdB=max(Dout_dB(1:numpt*1/2));
%plot([0:numpt/10-1].*fclk/numpt,Dout_dB(1:numpt/10)-maxdB);
plot([0:numpt/1-1].*fclk/numpt,Dout_dB(1:numpt/1)-maxdB);
grid on;

title('FFT PLOT');
xlabel('ANALOG INPUT FREQUENCY (Hz)');
ylabel('AMPLITUDE (dB)');
a1=axis; axis([a1(1) a1(2) -140 a1(4)]);

%Calculate SNR, SINAD, THD and SFDR values
%Find the signal bin number, DC = bin 1
fin=find(Dout_dB(1:numpt/2)==maxdB);

spanh=1;%spanh=2;
%Determine power spectrum
spectP=(abs(Dout_spect)).*(abs(Dout_spect));
%Find DC offset power
%Pdc=sum(spectP(1:span));
%Extract overall signal power
Ps=sum(spectP(fin-spanh:fin+spanh));

%Pn=sum(spectP(1:numpt/(2*32)))-Ps;%Pn噪声功率Ps信号功率
Pn=sum(spectP(1:numpt/2))-Ps;%Pn噪声功率Ps信号功率
%Vector/matrix to store both frequency and power of signal and harmonics
Fh=[];
%The 1st element in the vector/matrix represents the signal, the next element represents
%the 2nd harmonic, etc.
Ph=[];
%Find harmonic frequencies and power components in the FFT spectrum
for har_num=1:10 %har_num谐波总数
%Input tones greater than fSAMPLE are aliased back into the spectrum
tone=rem((har_num*(fin-1)+1)/numpt,1); %rem（x，y）x除以y的余数numpt(Number of Points)
if tone>0.5
%Input tones greater than 0.5*fSAMPLE (after aliasing) are reflected
tone=1-tone;
end
Fh=[Fh tone];
%For this procedure to work, ensure the folded back high order harmonics do not overlap
%with DC or signal or lower order harmonics
%har_peak=max(spectP(round(tone*numpt)-spanh:round(tone*numpt)+spanh));
%har_bin=find(spectP(round(tone*numpt)-spanh:round(tone*numpt)+spanh)==har_peak);
%har_bin=har_bin+round(tone*numpt)-spanh-1;
%Ph=[Ph sum(spectP(har_bin-1:har_bin+1))];
%Ph=[Ph sum(spectP(har_num*(fin-1):har_num*(fin-1)+2))];
end
%Determine the total distortion power
%Pd=sum(Ph(2:10)); %Pd总失真功率Ph(1) is fundamental harmonic谐波 power
%Determine the noise po*wer

format;%设置输出格式
SNDR =10*log10(Ps/Pn)%信噪比

% SINAD=10*log10(Ps/(Pn+Pd)) % SINAD = 10*log10(Ps/(Pn+Pd))信号与噪声失真比
% disp('THD is calculated from 2nd through 10th order harmonics');
% SFDR=10*log10(Ph(1)/max(Ph(2:10)))%SFDR无杂散动态范围
% ENOB = (SINAD-1.76)/6.02
% disp('Signal & Harmonic Power Components:');
% HD=10*log10(Ph(1:10)/Ph(1))