firnyquist

Lowpass Nyquist (Lth-band) FIR filter

Syntax

b = firnyquist(n,l,r) b = firnyquist('minorder',l,r,dev) b = firnyquist(n,l,r,decay) b = firnyquist(n,l,r,'nonnegative') b = firnyquist(n,l,r,'minphase')

Description

b = firnyquist(n,l,r)designs an Nth order, Lth band, Nyquist FIR filter with a rolloff factorrand an equiripple characteristic.

滚边的因素ris related to the normalized transition widthtwbytw=2π(r/l)(rad/sample). The order,n, must be even.lmust be an integer greater than one. Iflis not specified, it defaults to4.rmust satisfy0< r < 1. Ifris not specified, it defaults to0.5.

b = firnyquist('minorder',l,r,dev)designs a minimum-order, Lth band Nyquist FIR filter with a rolloff factorrusing the Kaiser window. The peak ripple is constrained by the scalardev.

b = firnyquist(n,l,r,decay)designs an Nth order (n), Lth band (l), Nyquist FIR filter where the scalardecay, specifies the rate of decay in the stopband.decaymust be nonnegative. If you omit or leave it empty,decaydefaults to0which yields an equiripple stopband.Anonequiripple stopband (decay≠0) may be desirable for decimation purposes.

b = firnyquist(n,l,r,'nonnegative')returns an FIR filter with nonnegative zero-phase response. This filter can be spectrally factored into minimum-phase and maximum-phase “square-root” filters. This allows you to use the spectral factors in applications such as matched-filtering.

b = firnyquist(n,l,r,'minphase')returns the minimum-phase spectral factorbminof ordern.bminmeets the conditionb=conv(bmin,bmax)so thatbis an Lth band FIR Nyquist filter of order 2n with filter rolloff factorr. Obtainbmax, the maximum phase spectral factor by reversing the coefficients ofbmin. For example,bmax = bmin(end:-1:1).

Examples

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Design a Nyquist Filter Using firnyquist

打开生活的脚本

This example designs a minimum phase factor of a Nyquist filter.

bmin = firnyquist(47,10,.45,'minphase'); b = firnyquist(2*47,10,.45,'nonnegative'); [h,w,s] = freqz(b); hmin = freqz(bmin); fvtool(b,1,bmin,1);

Figure Magnitude Response (dB) contains an axes object. The axes object with title Magnitude Response (dB) contains 2 objects of type line.

This example compares filters with different decay rates.

b1 = firnyquist(72,8,.3,0);% Equirippleb2 = firnyquist(72,8,.3,15); b3 = firnyquist(72,8,.3,25); fvtool(b1,1,b2,1,b3,1);

Figure Magnitude Response (dB) contains an axes object. The axes object with title Magnitude Response (dB) contains 3 objects of type line.

References

T. Saramaki, Finite Impulse Response Filter Design,Handbook for Digital Signal Processing, Mitra, S.K. and J.F. Kaiser Eds. Wiley-Interscience, N.Y., 1993, Chapter 4.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

All inputs must be constant. Expressions or variables are allowed if their values do not change.

Version History

Introduced in R2011a