ocmsp_iir_order

1 Description
2 Syntax
3 Parameters
4 Return
5 Examples
6 Remark
7 See Also
8 header to Included
9 Reference

Description

Estimate the minimum order of a digital/analog IIR filter required to meet a set of filter design specifications: loses no more than Rp dB in passband and has at least Rs dB of attenuation in the stopband.

Syntax

int ocmsp_iir_order( UINT * pN, double * pWn, double Wp, double Ws, double Rp, double Rs, int type, double * pWn2 = NULL, double Wp2 = -1.0, double Ws2 = -1.0 )

Parameters

pN: [output] returned lowest order N
pWn: [output] natural frequency of the filter, for filter design with ocmsp_IIR_filter
Wp: [input] passband edge frequency, it's in radians/second if is analog type, and should be normalized to [0, 1] if is digital (where 1 corresponds to pi radians/sample)
Ws: [input] stopband edge frequency, it's in radians/second if is analog type, and should be normalized to [0, 1] if is digital(where 1 corresponds to pi radians/sample)
Rp: [input] passband ripple in dB. It's the maximum permissible passband loss in decibels
Rs: [input] stopband attenuation in dB. It's the number of decibels the stopband is down from the passband
type: [input] filter type. It specifies the filter prototype(Butterworth, Chebyshev Type I, Chebyshev Type II, Elliptic or Bessel), band type (lowpass, highpass, bandstop or bandpass) and digital or analog type. For example; OMSP_BUTTERWORTH|OMSP_LOWPASS|OMSP_DIGITAL means a lowpass Butterworth digital filter.
pWn2: [output] natural frequency 2, only needed when it's a bandpass or bandstop filter
Wp2: [input][optional] passband edge frequency, it's in radians/second if is analog type, and should be normalized to [0, 1] if is digital (where 1 corresponds to pi radians/sample). Only needed when it's a bandpass or bandstop filter
Ws2: [input][optional] stopband edge frequency, it's in radians/second if is analog type, and should be normalized to [0, 1] if is digital(where 1 corresponds to pi radians/sample). Only needed when it's a bandpass or bandstop filter

The stopband and passband frequency range should follow:

Filter Type	Stopband/Passband conditions	Stopband	Passband
Lowpass	Wp < Ws	(Ws, 1)	(0, Wp)
Highpass	Wp > Ws	(0, Ws)	(Wp, 1)
Bandpass	Ws < Wp < Wp2 < Ws2	(0, Ws) and (Ws2, 1)	(Wp, Wp2)
Bandstop	Wp < Ws < Ws2 < Wp2	(0, Wp) and (Wp2, 1)	(Ws, Ws2)

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_order_ex1()
{
    int type = OMSP_BUTTERWORTH|OMSP_BANDPASS|OMSP_DIGITAL;
    double Wn[2] = {0.0, 0.0}, Wp[2] = {60.0/500, 200.0/500}, Ws[2] = {50.0/500, 250.0/500};
    double Rp = 3, Rs = 40;
    UINT N = 0;

    int nRet = 0;
    if (0 != (nRet = ocmsp_iir_order(&N, &Wn[0], Wp[0], Ws[0], Rp, Rs, type, &Wn[1], Wp[1], Ws[1])))
    {
        printf("ocmsp_iir_order failed, error code=%d\n", nRet);
        return;
    }

    printf("N = %d, Wn = [%lf, %lf]\n", N, Wn[0], Wn[1]);
}