Convert digital filter to transfer function




[num,den] = tf(d) converts a digital filter, d, to numerator and denominator vectors.


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Highpass Filter Transfer Function

Design a highpass FIR filter of order 8 with passband frequency 75 kHz and passband ripple 0.2 dB. Specify a sample rate of 200 kHz. Compute the coefficients of the equivalent transfer function.

hpFilt = designfilt('highpassiir','FilterOrder',8, ...
         'PassbandFrequency',75e3,'PassbandRipple',0.2, ...
[b,a] = tf(hpFilt)
b =
   1.0e-03 *
    0.0128   -0.1024    0.3583   -0.7166    0.8958   -0.7166    0.3583   -0.1024    0.0128
a =
    1.0000    5.7637   15.4847   25.1134   26.7644   19.1396    8.9554    2.5058    0.3212

Input Arguments

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d — Digital filterdigitalFilter object

Digital filter, specified as a digitalFilter object. Use designfilt to generate a digital filter based on frequency-response specifications.

Example: d = designfilt('lowpassiir','FilterOrder',3,'HalfPowerFrequency',0.5) specifies a third-order Butterworth filter with normalized 3-dB frequency 0.5π rad/sample.

Output Arguments

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num — Numerator coefficientsrow vector

Numerator coefficients, returned as a row vector.

Data Types: double

den — Denominator coefficientsrow vector

Denominator coefficients, returned as a row vector.

Data Types: double

See Also

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Introduced in R2014a

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