?
BilinearDesignLH.cpp@0:cacfc9e25452, 2019-06-04 (annotated)
- Committer:
- phungductung
- Date:
- Tue Jun 04 21:58:08 2019 +0000
- Revision:
- 0:cacfc9e25452
?;
Who changed what in which revision?
User | Revision | Line number | New contents of line |
---|---|---|---|
phungductung | 0:cacfc9e25452 | 1 | //------------------------------------------------------------------------------ |
phungductung | 0:cacfc9e25452 | 2 | // Design of Butterworth LPF and HPF using bilinear transform |
phungductung | 0:cacfc9e25452 | 3 | // |
phungductung | 0:cacfc9e25452 | 4 | // 2016/03/31, Copyright (c) 2016 MIKAMI, Naoki |
phungductung | 0:cacfc9e25452 | 5 | //------------------------------------------------------------------------------ |
phungductung | 0:cacfc9e25452 | 6 | |
phungductung | 0:cacfc9e25452 | 7 | #include "BilinearDesignLH.hpp" |
phungductung | 0:cacfc9e25452 | 8 | |
phungductung | 0:cacfc9e25452 | 9 | namespace Mikami |
phungductung | 0:cacfc9e25452 | 10 | { |
phungductung | 0:cacfc9e25452 | 11 | // Execute design |
phungductung | 0:cacfc9e25452 | 12 | // input |
phungductung | 0:cacfc9e25452 | 13 | // fc: Cutoff frequency |
phungductung | 0:cacfc9e25452 | 14 | // pb: Passband (LPF or HPF) |
phungductung | 0:cacfc9e25452 | 15 | // output |
phungductung | 0:cacfc9e25452 | 16 | // c : Coefficients for cascade structure |
phungductung | 0:cacfc9e25452 | 17 | // g : Gain factor for cascade structure |
phungductung | 0:cacfc9e25452 | 18 | void BilinearDesign::Execute(float fc, Type pb, Coefs c[], float& g) |
phungductung | 0:cacfc9e25452 | 19 | { |
phungductung | 0:cacfc9e25452 | 20 | Butterworth(); |
phungductung | 0:cacfc9e25452 | 21 | Bilinear(fc); |
phungductung | 0:cacfc9e25452 | 22 | ToCascade(pb); |
phungductung | 0:cacfc9e25452 | 23 | GetGain(pb); |
phungductung | 0:cacfc9e25452 | 24 | GetCoefs(c, g); |
phungductung | 0:cacfc9e25452 | 25 | } |
phungductung | 0:cacfc9e25452 | 26 | |
phungductung | 0:cacfc9e25452 | 27 | // Get poles for Butterworth characteristics |
phungductung | 0:cacfc9e25452 | 28 | void BilinearDesign::Butterworth() |
phungductung | 0:cacfc9e25452 | 29 | { |
phungductung | 0:cacfc9e25452 | 30 | float pi_2order = PI_/(2.0f*ORDER_); |
phungductung | 0:cacfc9e25452 | 31 | for (int j=0; j<ORDER_/2; j++) // Pole with imaginary part >= 0 |
phungductung | 0:cacfc9e25452 | 32 | { |
phungductung | 0:cacfc9e25452 | 33 | float theta = (2.0f*j + 1.0f)*pi_2order; |
phungductung | 0:cacfc9e25452 | 34 | sP_[j] = Complex(-cosf(theta), sinf(theta)); |
phungductung | 0:cacfc9e25452 | 35 | } |
phungductung | 0:cacfc9e25452 | 36 | } |
phungductung | 0:cacfc9e25452 | 37 | |
phungductung | 0:cacfc9e25452 | 38 | // Bilinear transform |
phungductung | 0:cacfc9e25452 | 39 | // fc: Cutoff frequency |
phungductung | 0:cacfc9e25452 | 40 | void BilinearDesign::Bilinear(float fc) |
phungductung | 0:cacfc9e25452 | 41 | { |
phungductung | 0:cacfc9e25452 | 42 | float wc = tanf(fc*PI_FS_); |
phungductung | 0:cacfc9e25452 | 43 | for (int k=0; k<ORDER_/2; k++) |
phungductung | 0:cacfc9e25452 | 44 | zP_[k] = (1.0f + wc*sP_[k])/(1.0f - wc*sP_[k]); |
phungductung | 0:cacfc9e25452 | 45 | } |
phungductung | 0:cacfc9e25452 | 46 | |
phungductung | 0:cacfc9e25452 | 47 | // Convert to coefficients for cascade structure |
phungductung | 0:cacfc9e25452 | 48 | void BilinearDesign::ToCascade(Type pb) |
phungductung | 0:cacfc9e25452 | 49 | { |
phungductung | 0:cacfc9e25452 | 50 | for (int j=0; j<ORDER_/2; j++) |
phungductung | 0:cacfc9e25452 | 51 | { |
phungductung | 0:cacfc9e25452 | 52 | ck_[j].a1 = 2.0f*real(zP_[j]); // a1m |
phungductung | 0:cacfc9e25452 | 53 | ck_[j].a2 = -norm(zP_[j]); // a2m |
phungductung | 0:cacfc9e25452 | 54 | ck_[j].b1 = (pb == LPF) ? 2.0f : -2.0f; // b1m |
phungductung | 0:cacfc9e25452 | 55 | ck_[j].b2 = 1.0f; // b2m |
phungductung | 0:cacfc9e25452 | 56 | } |
phungductung | 0:cacfc9e25452 | 57 | } |
phungductung | 0:cacfc9e25452 | 58 | |
phungductung | 0:cacfc9e25452 | 59 | // Calculate gain factor |
phungductung | 0:cacfc9e25452 | 60 | void BilinearDesign::GetGain(Type pb) |
phungductung | 0:cacfc9e25452 | 61 | { |
phungductung | 0:cacfc9e25452 | 62 | float u = (pb == LPF) ? 1.0f : -1.0f; |
phungductung | 0:cacfc9e25452 | 63 | float g0 = 1.0f; |
phungductung | 0:cacfc9e25452 | 64 | for (int k=0; k<ORDER_/2; k++) |
phungductung | 0:cacfc9e25452 | 65 | g0 = g0*(1.0f - (ck_[k].a1 + ck_[k].a2*u)*u)/ |
phungductung | 0:cacfc9e25452 | 66 | (1.0f + (ck_[k].b1 + ck_[k].b2*u)*u); |
phungductung | 0:cacfc9e25452 | 67 | gain_ = g0; |
phungductung | 0:cacfc9e25452 | 68 | } |
phungductung | 0:cacfc9e25452 | 69 | |
phungductung | 0:cacfc9e25452 | 70 | // Get coefficients |
phungductung | 0:cacfc9e25452 | 71 | void BilinearDesign::GetCoefs(Coefs c[], float& gain) |
phungductung | 0:cacfc9e25452 | 72 | { |
phungductung | 0:cacfc9e25452 | 73 | for (int k=0; k<ORDER_/2; k++) c[k] = ck_[k]; |
phungductung | 0:cacfc9e25452 | 74 | gain = gain_; |
phungductung | 0:cacfc9e25452 | 75 | } |
phungductung | 0:cacfc9e25452 | 76 | } |