前面有做过ADC性能测试，测试方式是先使用ADC采集一个单频信号，然后利用matlab进行性能分析。
下面把matlab分析的代码记录下来：
1 %The following program code plots the FFT spectrum of a desired test tone. Test tone based on coherent sampling criteria, and 2 %computes SNR, SINAD, THD and SFDR. 3 %This program is believed to be accurate and reliable. This program may get altered without prior notification.; 4 5 %fid=fopen('F:\pelican_ADC_test\vjtag_prj\data_analysis\single_tone.txt','r'); 6 %numpt=input('Number of Points in FFT? '); 7 %fclk=input('Sampling Frequency (MHz)? '); 8 %numbit=input('ADC Resolution (bits)? '); 9 close all; 10 clear all; 11 12 numpt=4096; 13 fclk=455/16; 14 % fclk=455/16/14; 15 numbit=12; 16 17 % a=textread('dds_data_out.txt','%s')';%以字符形式打开文件 18 % a=dlmread('sample_data.txt','%s')';%以字符形式打开文件 19 a=dlmread('sample_data.txt','%s')';%以字符形式打开文件 20 v1=a'; %16进制转化为10进制数，存储进v1矩阵 21 % for i = 1:numpt 22 % v1(i) = bitxor(v1(i),15872); 23 % end 24 25 %v1 is a column vector(1:numpt), and count is its length 26 %v1=dlmread('F:\pelican_ADC_test\vjtag_prj\data_analysis\single_tone.txt',''); 27 %fclose(fid); 28 %change v1 into a row vector 29 code=v1'; 30 31 %Warning: ADC output may be clipping - reduce input amplitude 32 if (max(code)==2^numbit-1) | (min(code)==0) 33 disp('WARNING: ADC OUTPUT MAYBE CLIPPING - CHECK INPUT AMPLITUDE!'); 34 end 35 36 figure; 37 plot(code); 38 title('TIME DOMAIN') 39 xlabel('SAMPLES'); 40 ylabel('DIGITAL OUTPUT CODE'); 41 Dout=code-(2^numbit-1)/2; %Re-center the digitized sinusoidal input 42 Voltage=Dout./((2^numbit-1)/2)*(0.5); 43 figure; 44 plot([1:numpt],Voltage); 45 46 Doutw=(Dout').*blackmanharris(numpt); %add Minimum 4-term Blackman-Harris window 47 Dout_spect=fft(Doutw); 48 Dout_dB=20*log10(abs(Dout_spect)); 49 50 figure; 51 maxdB=max(Dout_dB(1:numpt/2)); %numpt points FFT result in numpt/2 points spectrum 52 53 %计算距离满量程的幅度差 54 max_voltage=max(Voltage); 55 delta_amplitude=20*log10(max_voltage/0.5); %full scale voltage amplitude is 0.5v 56 57 plot([0:numpt/2-1].*fclk/numpt,Dout_dB(1:numpt/2)-maxdB+delta_amplitude); 58 grid on; 59 title('SINGLE TONE FFT PLOT'); 60 xlabel('ANALOG INPUT FREQUENCY (MHz)'); 61 ylabel('AMPLITUDE (dBfs)'); 62 a1=axis; axis([a1(1) a1(2) -140 a1(4)]); 63 fin=find(Dout_dB(1:numpt/2)==maxdB); %Find the signal bin (DC represents bin=1) 64 DC_span=6; %default DC leakage bins are 6 bins 65 signal_span = 10; %signal leakage bins are ±10 bins for minumun 4-term black-harris window 66 spanh=3; %%default harmonic leakage bins are ±3 bins 67 spectP=(abs(Dout_spect)).*(abs(Dout_spect)); 68 %Determine power level 69 Pdc=sum(spectP(1:DC_span)); %Determine DC offset power level 70 Ps=sum(spectP(fin-signal_span:fin+signal_span)); %Determine signal power level 71 Fh=[]; 72 %Vector storing frequency and power components of signal and harmonics 73 Ph=[]; %HD1=signal, HD2=2nd harmonic, HD3=3rd harmonic, etc. 74 75 %Find the harmonic frequencies/power within the FFT plot 76 for har_num=1:10 77 tone=rem((har_num*(fin- 1)+1)/numpt,1); %Note: tones > fSAMPLE are aliased back 78 if tone>0.5 79 tone=1-tone; 80 end 81 Fh=[Fh tone]; 82 83 %For this method to work properly, make sure that the folded back high order harmonics do not overlap with DC and signal 84 %components or lower order harmonics. 85 har_peak=max(spectP(round(tone*numpt)-spanh:round(tone*numpt)+spanh)); 86 har_bin=find(spectP(round(tone*numpt)-spanh:round(tone*numpt)+spanh)==har_peak); 87 har_bin=har_bin+round(tone*numpt)-spanh- 1; %make sure that the folded back high order harmonics do not overlap with DC and signal components or lower order harmonics 88 Ph=[Ph sum(spectP(har_bin-3:har_bin+3))]; 89 end 90 91 Pd=sum(Ph(2:10)); %Total distortion power level 92 Pn=sum(spectP(1:numpt/2))-Pdc-Ps-Pd; %Extract noise power level 93 format; 94 A=(max(code)-min(code))/(2^numbit) %Analog input amplitude in mV 95 AdB=20*log10(A) %Analog input amplitude in dB 96 SNR=10*log10(Ps/Pn) %SNR in dB 97 SINAD=10*log10(Ps/(Pn+Pd)) %SINAD in dB 98 disp('THD - HD2 through HD9'); 99 THD=10*log10(Pd/Ph(1)) %THD in dB 100 SFDR=10*log10(Ph(1)/max(Ph(2:10))) %SFDR in dB 101 disp('SIGNAL AND HARMONIC POWER (dB)'); 102 HD=10*log10(Ph(1:10)/Ph(1)) 103 104 hold on; 105 plot(Fh(2)*fclk,-70,'bo',Fh(3)*fclk,-70,'bx',Fh(4)*fclk,-70,'b+',Fh(5)*fclk,-70,'b*',Fh(6)*fclk,-70,'bs',Fh(7)*fclk,-70,'bd',Fh(8)*fclk,-70,'bv',Fh(9)*fclk,-70,'b^'); 106 legend('SIGNAL','HD2','HD3','HD4','HD5','HD6','HD7','HD8','HD9'); 107 hold off;
输出结果
1 A = 2 3 0.5432 4 5 6 AdB = 7 8 -5.3006 9 10 11 SNR = 12 13 54.0005 14 15 16 SINAD = 17 18 53.4240 19 20 THD - HD2 through HD9 21 22 THD = 23 24 -62.4784 25 26 27 SFDR = 28 29 63.0618 30 31 SIGNAL AND HARMONIC POWER (dB) 32 33 HD = 34 35 0 -63.0618 -78.1190 -79.6691 -82.4058 -86.1153 -90.7795 -91.1868 -89.8460 -74.6853
会标记出谐波的位置。
