import numpy as np
import scipy.signal as signal
import matplotlib.pyplot as plt

b, a = signal.iirdesign(wp=100, ws=200, gpass=2.0, gstop=40., analog=True)
w, h = signal.freqs(b, a)

plt.title('Analog filter frequency response')
plt.plot(w, 20*np.log10(np.abs(h)))
plt.ylabel('Amplitude Response [dB]')
plt.xlabel('Frequency')
plt.grid()
plt.show()


z, p, k = signal.tf2zpk(b, a)

plt.plot(np.real(z), np.imag(z), 'xb')
plt.plot(np.real(p), np.imag(p), 'or')
plt.legend(['Zeros', 'Poles'], loc=2)

plt.title('Pole / Zero Plot')
plt.ylabel('Real')
plt.xlabel('Imaginary')
plt.grid()
plt.show()