tf

Convert discrete-time filter System object to transfer function

Description

example

[num,den] = tf(sysobj) converts the discrete-time filter System object™ to numerator and denominator coefficient vectors of the equivalent transfer function.

[num,den] = tf(sysobj,'Arithmetic',arithType) analyzes the filter System object based on the arithmetic specified in arithType.

For more input options, see tf.

Examples

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Compute the transfer function of a biquad filter using the tf function.

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

Input Arguments

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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 filter. The 'Arithmetic' property set to 'Fixed' applies only to filter System objects with fixed-point properties.

Output Arguments

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Numerator coefficients of the filter, returned as a row vector.

Data Types: double

Denominator coefficients of the filter, returned as a row vector.

Data Types: double

Introduced in R2011a