2.1.22.3.9 ocmsp_iir_filter_ss

Description

Design digital or analog IIR filters with given specifications. It returns filter represented in state-space form:

x = Ax + Bu

y = Cx + Du

Syntax

int ocmsp_iir_filter_ss( UINT N, double Wn, double * pA, double * pB, double * pC, double * pd, int type, double Rp = 0.0, double Rs = 0.0, double Wn2 = -1.0 )

Parameters

N

[input] filter order, should be even if is bandpass or bandstop type

Wn

[input] cutoff or passband/stopband edge frequency, it's in radians/second if is analog type, and should be normalized to [0, 1] if is digital type, where 1 corresponds to half the sample rate

pA

[output] returned matrix A, size N-by-N

pB

[output] returned vector B, size N

pC

[output] returned vector C, size N

pd

[output] returned scalar d

type

[intput] filter type, it specifies the filter prototype(Butterworth, Shebyshev Type I, Chebyshev Type II, Elliptic or Bessel), bandtype(lowpass, highpass, bandstop or bandpass) and digital or analog type. For example

OMSP_BUTTERWORTH|OMSP_LOWPASS|OMSP_DIGITAL means a lowpass Butterworth digital filter.

Rp

[input][optional] passband ripple (dB), needed when it's Chebyshev Type I or Elliptic type

Rs

[input][optional] stopband attenuation (dB), needed when it's Chebyshev Type II or Elliptic type

Wn2

[input][optional] cutoff or passband/stopband-edge frequency. Needed when it's a bandpass or bandstop filter. It's in radians/second if is analog type, and should be normalized to [0, 1] if is digital type (where 1 corresponds to half the sample rate).

Return

Return OE_NOERROR if succeed, otherwise, non-zero error code is returned (OE_NULL_POINTER, OE_INVALID_FREQ, OE_INVALID_BANDFREQS, OE_INVLAID_RIPPLE, OE_INVALID_BANDRIPPLES or OE_INVALID_TYPE)

Examples

EX1

#include <ocmsp.h>
void ocmsp_iir_filter_ss_ex1()
{
    UINT N = 18; //even number if bandpass or bandstop
    double Wn[2] = {300.0/500, 400.0/500};
    matrix A(N, N); //size NxN
    vector B(N), C(N); //size N
    double d;
    int type = OMSP_BUTTERWORTH|OMSP_BANDPASS|OMSP_DIGITAL;

    int nRet = 0;
    if (0 != (nRet = ocmsp_iir_filter_ss(N, Wn[0], A, B, C, &d, type, 0.0, 0.0, Wn[1])))
    {
        printf("ocmsp_iir_filter_ss failed, error code=%d\n", nRet);
        return;
    }
}

Remark

See Also

ocmsp_iir_filter, ocmsp_iir_filter_sos, ocmsp_iir_filter_zp

Header to Included

ocmsp.h

Reference