复数信号采样率要求分析

%pylab inline
pylab.rcParams['figure.figsize'] = (10, 6)
from scipy.signal import *

Populating the interactive namespace from numpy and matplotlib

def gensig(sr, fs):
    """
    sr - sample rate @MHz
    fs - signal frequency @MHz
    """
    #sample time
    st = 1/sr #@us
    t = arange(1024)*st
    #signal frequency 
    fs = 5  #@MHz
    vi = cos(2*pi*fs*t)
    vq = sin(2*pi*fs*t)
    return vi, vq

def checkfft(x, tname, full, sr):
    fout = fft.fft(x)
    if not full:
        fout = fft.fftshift(fout)
    amp = 20*log10(abs(fout) + 1e-5)
    #fft range is [-sample_frequency/2, sample_frequency/2]
    nfft = len(amp)
    if full:
        fin  = sr*(arange(nfft)/float(nfft))
    else:
        fin  = sr*(arange(nfft)/float(nfft) - 0.5)
    figure()
    plot(fin, amp)
    grid(True)
    title(tname)

#5MHz signal @40MHz sample rate
sr = 40.0
fs = 5.0
vi, vq = gensig(sr, fs)
#now check the fft of real signal
checkfft(vi, 'real signal', False, sr)
#now check fft of complex signal
checkfft(vi+1j*vq, 'complex signal', True, sr)


#5MHz @6MHz sample rate
sr = 6.0
vi, vq = gensig(sr, fs)
#now check the fft of real signal
checkfft(vi, 'real signal', False, sr)
#now check fft of complex signal
checkfft(vi+1j*vq, 'complex signal', True, sr)

output_1_0.png output_1_1.png output_1_2.png output_1_3.png