DDC设计MATLAB.zip

% Routine to compute the frequency response of a set of filters in the ISL5416. % The filter parameters are set by calling the file init1.m before calling this % routine. % Filtresp computes and displays the composite frequency response of % The CIC filter followed by up to 3 decimating FIR filters. % If FIR1 or FIR2 is bypassed, use 'impulse.imp' as the file name % and 1 as the decimation factor. The filter order is CIC -> FIR1 -> FIR2. % Compute the total number of points to display-- % 256 points of resolution at the output sample rate. points = 256 * fir2deci * fir1deci * displaylobes; startfreq = 0; stepsize = fsamp / (cicdeci / displaylobes) / points; stopfreq = stepsize * (points - 1); freq = [0:1:points-1] * fsamp / (cicdeci / displaylobes) / points; % Compute the CIC response. phs = [1:1:points-1] / (points / displaylobes); phs = phs * pi; cicresp = 20 * stages * log10(0.0000000001 + abs((sin(phs) ./ sin(phs/cicdeci)) / cicdeci)); cicresp = [0 cicresp]; % Compute the FIR1 frequency response fir1 = fgetimp(firfile1); fir1 = round(fir1*(2^19))/(2^19); % round to 20 bits fir1resp = 20*log10(.00000001+abs(fft([fir1' zeros(1,points/(displaylobes)-size(fir1,1))]))); temp = fir1resp; for i=1:(displaylobes-1) fir1resp = [ fir1resp temp ]; end % Compute the FIR2 frequency response fir2 = fgetimp(firfile2); fir2 = round(fir2*(2^19))/(2^19); % round to 20 bits fir2resp = 20*log10(.00000001+abs(fft([fir2' zeros(1,points/(displaylobes*fir1deci)-size(fir2,1))]))); temp = fir2resp; for i=1:(fir1deci*displaylobes-1) fir2resp = [ fir2resp temp ]; end % Compute the overall response overallresp = cicresp + fir1resp + fir2resp; % Set a magnitude floor (-160 dB) for i=1:points if overallresp(i) < -160 overallresp(i) = -160; end if cicresp(i) < -160 cicresp(i) = -160; end if fir1resp(i) < -160 fir1resp(i) = -160; end if fir2resp(i) < -160 fir2resp(i) = -160; end end points startfreq stopfreq stepsize % Plot the frequency response. hold off plot(freq + j * cicresp,'g') hold on plot(freq + j * fir1resp,'c') plot(freq + j * fir2resp,'r') plot((freq +j * (overallresp)),'k') legend('CIC', 'FIR 1', 'FIR 2', 'OVERALL'); xlabel('Frequency in Hz'); ylabel('dBFS'); title('CIC -> FIR1 -> FIR2 Frequency Response'); axis([0 40e6 -160 0]); zoom on grid