Python、FFT和DC偏置分析

Question

我在占空比为 50% 的方波信号（100Hz，0V-5V）上测试了 FFT，但我不明白为什么我的直流偏移很大？

理论上应该是2.5V？

谢谢，最好的问候。

基波正常，其他谐波正常

square signal 100Hz, TTL compatible 0V-5V, 50% duty cycle

FFT, DC offset problem, fundamental ok, harmonics ok

from scipy.fftpack import fft
from scipy import signal
import matplotlib.pyplot as plt
import numpy as np

#
# configuration
# time analyse = L * (1/Fsample)
#
L = 512 # lenght buffer
Fsample = 2000 # frequency sample
Fsignal = 100 # frequency

#********************************

# perdiode sample
Tsample = 1.0/Fsample

# time vector, start = 0s, stop = 0.1024s, step = (0.1024s / (1/Fe))
t = np.linspace(0.0, L*Tsample, L)

# signal definition, DC offet = 2.5V, Amplitude = 2.5V
signal = 2.5 + 2.5*signal.square(2 * np.pi * Fsignal * t, 0.5)

# plot time signal
plt.subplot(2,1,1)
plt.plot(t, signal)

# fft of time signal
yf = fft(signal)

# time vector of fft 
xf = np.linspace(0.0, 1.0/(2.0*Tsample), L//2)

# plot spectral
plt.subplot(2,1,2)
plt.plot(xf, 2.0/L * np.abs(yf[0:L//2]))

Answer 1

在最后一行，归一化因子是错误的。

不是 2/L，而是 1/L。

正确的归一化因子plt.plot(xf, 1.0/L * np.abs(yf[0:L//2]))

代码现在可以正常工作了！

FFT correct amplitude

Python、FFT和DC偏置分析

Python, FFT and DC offset analysis

python

fft

offset

dc