《DSP using MATLAB》Problem 8.12
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代码:
%% ------------------------------------------------------------------------ %% Output Info about this m-file fprintf(‘\\n***********************************************************\\n‘); fprintf(‘ <DSP using MATLAB> Problem 8.12 \\n\\n‘); banner(); %% ------------------------------------------------------------------------ Wp = 500; Ws = 2000; Rp = 0.25; As = 50; Fp = Wp/(2*pi); Fs = Ws/(2*pi); Ripple = 10 ^ (-Rp/20) Attn = 10 ^ (-As/20) % Analog filter design: [b, a] = afd(‘butter‘, Fp, Fs, Rp, As); %[b, a] = afd_butt(Wp, Ws, Rp, As); % Calculation of second-order sections: [C, B, A] = sdir2cas(b, a); % Calculation of Frequency Response: [db, mag, pha, ww] = freqs_m(b, a, 2500); % Calculation of Impulse Response: [ha, x, t] = impulse(b, a); %% ------------------------------------------------- %% Plot %% ------------------------------------------------- figure(‘NumberTitle‘, ‘off‘, ‘Name‘, ‘Problem 8.12 Analog Butterworth lowpass‘) set(gcf,‘Color‘,‘white‘); M = 1.0; % Omega max subplot(2,2,1); plot(ww, mag); grid on; axis([-2100, 2100, 0, 1.2]); xlabel(‘ Analog frequency in rad/sec units‘); ylabel(‘|H|‘); title(‘Magnitude in Absolute‘); set(gca, ‘XTickMode‘, ‘manual‘, ‘XTick‘, [-500, 0, 500, 2000]); set(gca, ‘YTickMode‘, ‘manual‘, ‘YTick‘, [0, 0.003, 0.97, 1]); subplot(2,2,2); plot(ww, db); grid on; %axis([0, M, -50, 10]); xlabel(‘Analog frequency in rad/sec units‘); ylabel(‘Decibels‘); title(‘Magnitude in dB ‘); set(gca, ‘XTickMode‘, ‘manual‘, ‘XTick‘, [-500, 0, 500, 2000]); set(gca, ‘YTickMode‘, ‘manual‘, ‘YTick‘, [-50, -1, 0]); set(gca,‘YTickLabelMode‘,‘manual‘,‘YTickLabel‘,[‘50‘;‘ 1‘;‘ 0‘]); subplot(2,2,3); plot(ww, pha/pi); grid on; axis([-2100, 2100, -1.2, 1.2]); xlabel(‘Analog frequency in rad/sec nuits‘); ylabel(‘radians‘); title(‘Phase Response‘); set(gca, ‘XTickMode‘, ‘manual‘, ‘XTick‘, [-500, 0, 500, 2000]); set(gca, ‘YTickMode‘, ‘manual‘, ‘YTick‘, [-1:0.5:1]); subplot(2,2,4); plot(t, ha); grid on; %axis([0, 30, -0.05, 0.25]); xlabel(‘time in seconds‘); ylabel(‘ha(t)‘); title(‘Impulse Response‘);
运行结果:
通带ripple和阻带衰减,将题中的dB单位转换为以绝对值为单位。
非归一化模拟Butterworth低通滤波器,直接形式(有理函数)的系数,
将H(s)转换成串联形式,即一系列二阶子滤波器的乘积形式
模拟滤波器的幅度谱、相位谱和脉冲响应序列。
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