时域特性:采用(512点)升余弦滚降,是通信领域里成熟技术的移植,容易实现。
频域特性:5MHz内频率特性完全平坦,-3dB带宽大于5.5MHz,充分保留画面细节,纤毫毕现。低达-28dB的响应在半采样频率,确保任何频谱反折分量都被掩盖于量化噪声之中,再亮的细线也不会污损画面。
// 如果有修改,记得告诉我
// Copyleft under FreeBSD License
clear all;
clc;
//(实际带宽-理想带宽)/理想带宽=滚降系数
//
function [t,h] = myraicos(a, Ns, Fb, Fs)
printf("调试信息:myraicos->a=%f:Ns=%d:Fb=%d:Fs=%d\n",a,Ns,Fb,Fs);
Ts = 1 ./ Fs;
Tb = 1 ./ Fb;
t = (-Ns):1:(Ns-1);
t = t .* Ts;
ha = (sin(%pi .* t ./ Tb) + %eps) ./ (%pi .* t ./ Tb + %eps);
hb = cos(a .* %pi .* t ./ Tb) ./ (1 - (2 .* a .* t ./ Tb).^2 + %eps);
h = ha .* hb;
endfunction
__Fs = 74.25e6; //MHz
__Rs = 1920;
__Rr = 5760;
__Fr = __Fs * __Rr / __Rs;
printf("\n");
printf("采样频率: %f MHz \n", __Fr/1e6);
printf("过采样倍数: %.1f x \n", __Rr/__Rs);
Ns = 512;
Fs = __Rr;
clf;
__x = (1 : 1 : Ns * 2) / Ns / 2 * __Fr / 1e6;
[t,h2] = myraicos(0.18, Ns, 300, Fs);
//plot(__x,20*log10(abs(fft(h2)+0.005)/max(abs(fft(h2)+0.005))),'red');
plot(t,h2)