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# phasez

Phase response of digital filter

## Syntax

```[phi,w] = phasez(b,a,n) [phi,w] = phasez(sos,n) [phi,w] = phasez(d,n) [phi,w] = phasez(...,n,'whole') phi = phasez(...,w) [phi,f] = phasez(...,n,fs) phi = phasez(...f,fs) [phi,w,s] = phasez(...) phasez(...) ```

## Description

`[phi,w] = phasez(b,a,n)` returns the `n`-point unwrapped phase response vector, `phi`, in radians and the frequency vector, `w`, in radians/sample for the filter coefficients specified in `b` and `a`. The values of the frequency vector, `w`, range from 0 to π. If `n` is omitted, the length of the phase response vector defaults to 512. For best results, set `n` to a value greater than the filter order.

`[phi,w] = phasez(sos,n)` returns the unwrapped phase response for the second order sections matrix, `sos`. `sos` is a K-by-6 matrix, where the number of sections, K, must be greater than or equal to 2. If the number of sections is less than 2, `phasez` considers the input to be the numerator vector, `b`. Each row of `sos` corresponds to the coefficients of a second-order (biquad) filter. The ith row of the `sos` matrix corresponds to ```[bi(1) bi(2) bi(3) ai(1) ai(2) ai(3)]```.

`[phi,w] = phasez(d,n)` returns the unwrapped phase response for the digital filter, `d`. Use `designfilt` to generate `d` based on frequency-response specifications.

`[phi,w] = phasez(...,n,'whole')` returns frequency and unwrapped phase response vectors evaluated at `n` equally-spaced points around the unit circle from 0 to 2π radians/sample.

`phi = phasez(...,w)` returns the unwrapped phase response in radians at frequencies specified in `w` (radians/sample). The frequencies are normally between 0 and π. The vector `w` must have at least two elements.

`[phi,f] = phasez(...,n,fs)` return the unwrapped phase vector `phi` in radians and the frequency vector in hertz. The frequency vector ranges from 0 to the Nyquist frequency, `fs/2`. If the `'whole'` option is used, the frequency vector ranges from 0 to the sampling frequency.

`phi = phasez(...f,fs)` return the phase response in radians at the frequencies specified in the vector `f` (in hertz) using the sampling frequency `fs` (in hertz). The vector `f` must have at least two elements.

`[phi,w,s] = phasez(...)` return plotting information, where `s` is a structure array with fields you can change to display different frequency response plots.

`phasez(...)` with no output arguments plots the phase response of the filter. If you input the filter coefficients or second order sections matrix, the current figure window is used. If you input a `digitalFilter`, the step response is displayed in `fvtool`.

### Note

If the input to `phasez` is single precision, the phase response is calculated using single-precision arithmetic. The output, `phi`, is single precision.

## Examples

collapse all

Use `designfilt` to design an FIR filter of order 54, normalized cutoff frequency $0.3\pi$ rad/s, passband ripple 0.7 dB, and stopband attenuation 42 dB. Use the method of constrained least squares. Display the phase response of the filter.

```Nf = 54; Fc = 0.3; Ap = 0.7; As = 42; d = designfilt('lowpassfir','CutoffFrequency',Fc,'FilterOrder',Nf, ... 'PassbandRipple',Ap,'StopbandAttenuation',As, ... 'DesignMethod','cls'); phasez(d)```

Design the same filter using `fircls1`. Keep in mind that `fircls1` uses linear units to measure the ripple and attenuation.

```pAp = 10^(Ap/40); Apl = (pAp-1)/(pAp+1); pAs = 10^(As/20); Asl = 1/pAs; b = fircls1(Nf,Fc,Apl,Asl); phasez(b)```

Design a lowpass equiripple filter with normalized passband frequency $0.45\pi$ rad/s, normalized stopband frequency $0.55\pi$ rad/s, passband ripple 1 dB, and stopband attenuation 60 dB. Display the phase response of the filter.

```d = designfilt('lowpassfir', ... 'PassbandFrequency',0.45,'StopbandFrequency',0.55, ... 'PassbandRipple',1,'StopbandAttenuation',60, ... 'DesignMethod','equiripple'); phasez(d)```

Design an elliptic lowpass IIR filter with normalized passband frequency $0.4\pi$ rad/s, normalized stopband frequency $0.5\pi$ rad/s, passband ripple 1 dB, and stopband attenuation 60 dB. Display the phase response of the filter.

```d = designfilt('lowpassiir', ... 'PassbandFrequency',0.4,'StopbandFrequency',0.5, ... 'PassbandRipple',1,'StopbandAttenuation',60, ... 'DesignMethod','ellip'); phasez(d)```