時域特性:採用(512點)升餘弦滾降,是通信領域裏成熟技術的移植,容易實現。
頻域特性:5MHz內頻率特性完全平坦,-3dB帶寬大於5.5MHz,充分保留畫面細節,纖毫畢現。低達-28dB的響應在半採樣頻率,確保任何頻譜反折分量都被掩蓋於量化噪聲之中,再亮的細線也不會污損畫面。
// 如果有修改,記得告訴我
// Copyleft under FreeBSD License
clear all;
clc;
//(實際帶寬-理想帶寬)/理想帶寬=滾降係數
//
function [t,h] = myraicos(a, Ns, Fb, Fs)
printf("調試信息: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("採樣頻率: %f MHz \n", __Fr/1e6);
printf("過採樣倍數: %.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)