% 16th Order Band-Pass Sigma-Delta Modulator Model% by A. Fornasari, P. Malcovati% The modulator structure is simulated using Simulink (OnePath.mdl).% 1. Plots the Power Spectral Density of the bit-stream % 2. Calculates the SNRclearphs=0;bw=5e6;                 % Signal BandwidthR=32;                   % Oversampling ratioFs=R*(2*bw);            % Sampling frequency		Ts=1/Fs;                % Sampling timeN=16384;                % Number of samplesw=hann_pv(N);           % Windowing Functionnper=36;                % Number of periodsfBL=N/4-((N/Fs)*bw/2);fBH=N/4+((N/Fs)*bw/2);Fin=nper*Fs/N+Fs/4;     % Input signal frequency (Fin = nper*Fs/N)Ampl=0.2-pi/1000;       % Input signal amplitude [V]f=Fin/Fs;	            % Normalized signal frequencyfinrad=Fin*2*pi;        % Input signal frequency (rad/s)Ntransient=2;Vref=1;%% Integrator parameters%k=1.38e-23;				% Boltzmann Constantctot=1e-12;				% Sampling CapacitanceNCOMPARATORI=8;match=9e-10;            % Realistic value, but not related to any technology (because of non disclosure agreement)t0=clock;B1i=10/7;B1f=B1i;B2i=1/2;B1lf=1/77;B3i=2;B4i=1/2;B4lf=1/14;B1ff=3;B2ff=2;B3ff=1;B4ff=1;SetReal;yy1=zeros(1,N);Vzero=zeros(1,32);%**************************************************************************************%%************************************Open Simulink*************************************%%**************************************************************************************%open_system('FourPaths')options=simset('InitialState', zeros(1,30), 'RelTol', 1e-3, 'MaxStep', 1/Fs);sim('FourPaths', (N+Ntransient)/Fs, options);%**************************************************************************************%%**************Calculates SNR and PSD of the bit-stream and of the signal**************%%**************************************************************************************%yy1=yout(2+Ntransient:1+N+Ntransient)';ptot=zeros(1,N);[snr,ptot,psigdB,pnoisedB]=calcSNR(yy1(1:N),f,fBL,fBH,w,N); Rbit=(snr-1.76)/6.02;figure(1);clf;plot(linspace(0,Fs/2,N/2), ptot(1:N/2), 'r');grid on;title('PSD of a 4th-Order 4-path Sigma-Delta Modulator')xlabel('Frequency [Hz]')ylabel('PSD [dB]')axis([0 Fs/2 -160 0]);figure(2);clf;semilogx(linspace(0,Fs/2,N/2), ptot(1:N/2), 'r');grid on;title('PSD of a 4th-Order 4-path Sigma-Delta Modulator')xlabel('Frequency [Hz]')ylabel('PSD [dB]')axis([Fs/8 Fs/2 -160 0]);figure(3);clf;plot(linspace(0,Fs/2,N/2), ptot(1:N/2), 'r');hold on;title('PSD of a 4th-Order 4-path Sigma-Delta Modulator (detail)')xlabel('Frequency [Hz]')ylabel('PSD [dB]')axis([Fs/4-Fs/R Fs/4+Fs/R -160 0]);grid on;hold off;text_handle = text(floor(Fs/4+1e6),-20, sprintf('SNR = %4.1fdB @ OSR=%d\n',snr,R));text_handle = text(floor(Fs/4+1e6),-40, sprintf('ENOB = %2.2f bits @ OSR=%d\n',Rbit,R));s1=sprintf('   SNR(dB)=%1.3f',snr);s2=sprintf('   Simulation time =%1.3f min',etime(clock,t0)/60);disp(s1)disp(s2)