《DSP using MATLAB》示例Example 6.27

Posted 2020-09-06 沧海一粟

代码：

% 
r = 0.9; theta = (pi/180)*[-55:5:-35, 35:5:55]\';
p = r*exp(j*theta); a = poly(p); b = 1;
w = [0:500]*pi/500; H = freqz(b*1e-4, a, w);
magH = abs(H); magHdb = 20*log10(magH);

% Direct form: quantized coefficients
N = 15; [ahat, L, B] = QCoeff(a, N);
TITLE = sprintf(\'%i-bit (1+%i+%i) Precision (DF)\', N+1, L, B);
Hhat = freqz(b*1e-4, ahat, w); magHhat = abs(Hhat);

% Cascade form: quantized coefficients: Same N
[b0, B0, A0] = dir2cas(b, a); [BAhat1, L1, B1] = QCoeff([B0, A0], N);
TITLE1 = sprintf(\'%i-bit (1+%i+%i) Precision (CF)\', N+1, L1, B1);
Bhat1 = BAhat1(:, 1:3); Ahat1 = BAhat1(:, 4:6);
[bhat1, ahat1] = cas2dir(b0, Bhat1, Ahat1);
Hhat1 = freqz(b*1e-4, ahat1, w); magHhat1 = abs(Hhat1);

% Cascade fomr: quantized coefficients: Same B (N=L1+B)
N1 = L1 + B; [BAhat2, L2, B2] = QCoeff([B0, A0], N1);
TITLE2 = sprintf(\'%i-bit (1+%i+%i) Precision (CF)\', N1+1, L2, B2);
Bhat2 = BAhat2(:, 1:3); Ahat2 = BAhat2(:, 4:6);
[bhat2, ahat2] = cas2dir(b0, Bhat2, Ahat2);
Hhat2 = freqz(b*1e-4, ahat2, w); magHhat2 = abs(Hhat2);


% Comparison of Magnitude Plots
Hf_1 = figure(\'paperunits\', \'inches\', \'paperposition\', [0, 0, 6, 4]);
%figure(\'NumberTitle\', \'off\', \'Name\', \'Exameple 6.26a\')
set(gcf,\'Color\',\'white\');

subplot(2, 2, 1); plot(w/pi, magH, \'g\', \'linewidth\', 2); axis([0, 1, 0, 0.7]);
xlabel(\'Digital Frequency in \\pi units\', \'fontsize\', 10);
ylabel(\'Magnitude Response\', \'fontsize\', 10); grid on;
title(\'Infinite Precision (DF)\', \'fontsize\', 10, \'fontweight\', \'bold\');

subplot(2, 2, 2); plot(w/pi, magHhat, \'r\', \'linewidth\', 2); axis([0, 1, 0, 0.7]);
xlabel(\'Digital Frequency in \\pi units\', \'fontsize\', 10);
ylabel(\'Magnitude Response\', \'fontsize\', 10); grid on;
title(TITLE, \'fontsize\', 10, \'fontweight\', \'bold\');

subplot(2, 2, 3); plot(w/pi, magHhat1, \'r\', \'linewidth\', 2); axis([0, 1, 0, 0.7]);
xlabel(\'Digital Frequency in \\pi units\', \'fontsize\', 10);
ylabel(\'Magnitude Response\', \'fontsize\', 10); grid on;
title(TITLE1, \'fontsize\', 10, \'fontweight\', \'bold\');

subplot(2, 2, 4); plot(w/pi, magHhat2, \'r\', \'linewidth\', 2); axis([0, 1, 0, 0.7]);
xlabel(\'Digital Frequency in \\pi units\', \'fontsize\', 10);
ylabel(\'Magnitude Response\', \'fontsize\', 10); grid on;
title(TITLE2, \'fontsize\', 10, \'fontweight\', \'bold\');

 运行结果：