Convert discrete-time filter System object to transfer function
Compute the transfer function of a biquad filter using the
Create a fourth-order, lowpass biquadratic filter object with a normalized cutoff frequency of 0.4.
[z,p,k] = ellip(4,1,60,0.4); % Set up the filter [s,g] = zp2sos(z,p,k); biquad = dsp.BiquadFilter(s,g,'Structure','Direct form I')
biquad = dsp.BiquadFilter with properties: Structure: 'Direct form I' SOSMatrixSource: 'Property' SOSMatrix: [2x6 double] ScaleValues: 0.0351 NumeratorInitialConditions: 0 DenominatorInitialConditions: 0 OptimizeUnityScaleValues: true Show all properties
Compute the transfer function of the designed biquadratic filter. The
tf function returns the numerator and the denominator coefficient vectors of the filter.
[num,den] = tf(biquad)
num = 1×5 0.0351 0.1038 0.1432 0.1038 0.0351
den = 1×5 1.0000 -1.5676 1.7412 -1.0104 0.3093
sysobj— Input filter
Input filter, specified as one of the following filter System objects:
arithType— Arithmetic type
Specify the arithmetic used during analysis. When the arithmetic input is not specified and
the filter System object is unlocked, the analysis tool assumes a double-precision
'Arithmetic' property set to
applies only to filter System objects with fixed-point properties.
num— Numerator coefficients
Numerator coefficients of the filter, returned as a row vector.
den— Denominator coefficients
Denominator coefficients of the filter, returned as a row vector.