Frequency response of Downsampled transfer function in Z domain #1126

roccafrancesco · 2025-02-15T11:53:29Z

roccafrancesco
Feb 15, 2025

Hello Everybody
I wrote a simple function that convert a z transfer function(num,den) in frequency response object when the outputl is decimated M fold.

#num: transfer function numerator
#den: transfer function denominator
#M: M fold decimator
#Tc: sample time
#points: points of frequency response

`def` downSampling(num,den,M,Tc,points):
    omega = np.logspace(np.log10(0.0001),np.log10(0.99*np.pi/(Tc)),num=points,endpoint=True)
    denFreq=np.zeros(omega.size,dtype=complex)
    numFreq=np.zeros(omega.size,dtype=complex) 
    bode=np.zeros(omega.size,dtype=complex) 
    M1=float(M)

    
    for k in range(M):
        
        zeta=np.exp(1.0j*omega*Tc/M)*np.exp(-2.0j*np.pi*k*Tc/M)
        denFreq=denFreq+np.polyval(den, zeta)
        numFreq=numFreq+np.polyval(num, zeta)  
        bode=bode+(numFreq/denFreq)
    bode=bode/M
   
    
    sys=ct.FrequencyResponseData(bode,omega,smooth=True)
    return sys

Im not really sure if i did everithig well.
Could someone check and correct eventually the function?
Thank you

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Frequency response of Downsampled transfer function in Z domain #1126

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roccafrancesco Feb 15, 2025

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roccafrancesco
Feb 15, 2025