branch for cuboid
IIR_filter.cpp
- Committer:
- altb2
- Date:
- 2019-03-07
- Revision:
- 0:72b60c5271cc
- Child:
- 2:8706bb4e8f93
File content as of revision 0:72b60c5271cc:
#include "IIR_filter.h" #include "mbed.h" using namespace std; /* IIR filter implemention for the following filter types: init for: first order differentiatior: G(s) = s/(T*s + 1) first order lowpass with gain G(s) = K/(T*s + 1) second order lowpass with gain G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0*w0) nth order, with arbitrary values the billinear transformation is used for s -> z reseting the filter only makes sence for static signals, whatch out if you're using the differnetiator */ // G(s) = s/(T*s + 1) IIR_filter::IIR_filter(float T, float Ts){ // filter orders nb = 1; // Filter Order na = 1; // Filter Order // filter coefficients B = (double*)malloc((nb+1)*sizeof(double)); A = (double*)malloc(na*sizeof(double)); B[0] = 2.0/(2.0*(double)T + (double)Ts); B[1] = -B[0]; A[0] = -(2.0*(double)T - (double)Ts)/(2.0*(double)T + (double)Ts); // signal arrays uk = (double*)malloc((nb+1)*sizeof(double)); yk = (double*)malloc(na*sizeof(double)); uk[0]= uk[1] = 0.0; yk[0] = 0.0; // dc-gain this->K = 0.0; } // G(s) = K/(T*s + 1) IIR_filter::IIR_filter(float T, float Ts, float K){ // filter orders nb = 1; // Filter Order na = 1; // Filter Order // filter coefficients B = (double*)malloc((nb+1)*sizeof(double)); A = (double*)malloc(na*sizeof(double)); B[0] = (double)Ts/((double)Ts + 2.0*(double)T); B[1] = B[0]; A[0] = ((double)Ts - 2.0*(double)T)/((double)Ts + 2.0*(double)T); // signal arrays uk = (double*)malloc((nb+1)*sizeof(double)); yk = (double*)malloc(na*sizeof(double)); uk[0]= uk[1] = 0.0; yk[0] = 0.0; // dc-gain this->K = (double)K; } // G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0^2) IIR_filter::IIR_filter(float w0, float D, float Ts, float K){ // filter orders nb = 2; // Filter Order na = 2; // Filter Order // filter coefficients B = (double*)malloc((nb+1)*sizeof(double)); A = (double*)malloc(na*sizeof(double)); double k0 = (double)Ts*(double)Ts*(double)w0*(double)w0; double k1 = 4.0*(double)D*(double)Ts*(double)w0; double k2 = k0 + k1 + 4.0; B[0] = (double)K*k0/k2; B[1] = 2.0*B[0]; B[2] = B[0]; A[0] = (2.0*k0 - 8.0)/k2; A[1] = (k0 - k1 + 4.0)/k2; // signal arrays uk = (double*)malloc((nb+1)*sizeof(double)); yk = (double*)malloc(na*sizeof(double)); uk[0]= uk[1] = uk[2] = 0.0; yk[0] = yk[1] = 0.0; // dc-gain this->K = (double)K; } IIR_filter::IIR_filter(float *b, float *a, int nb_, int na_){ // filter orders this->nb = nb_-1; // Filter Order this->na = na_; // Filter Order // filter coefficients B = (double*)malloc((nb+1)*sizeof(double)); A = (double*)malloc(na*sizeof(double)); uk = (double*)malloc((nb+1)*sizeof(double)); yk = (double*)malloc(na*sizeof(double)); for(int k=0;k<=nb;k++){ B[k]=b[k]; uk[k]=0.0; } for(int k=0;k<na;k++){ A[k] = a[k]; yk[k] = 0.0; } // dc-gain this->K = 1.0; } IIR_filter::~IIR_filter() {} void IIR_filter::reset(float val) { for(int k=0;k < nb;k++) uk[k] = (double)val; for(int k=0;k < na;k++) yk[k] = (double)val*K; } /* the filter is operating as follows: (B[0] + B[1]*z^-1 + ... + B[nb]*z^-nb)*U(z) = (1 + A[0]*z^-1 + ... + A[na-1]*z^-na))*Y(z) y(n) = B[0]*u(k) + B[1]*u(k-1) + ... + B[nb]*u(k-nb) + ... - A[0]*y(k-1) - A[1]*y(k-2) - ... - A[na]*y(n-na) */ float IIR_filter::filter(double input){ for(int k = nb;k > 0;k--) // shift input values back uk[k] = uk[k-1]; uk[0] = input; double ret = 0.0; for(int k = 0;k <= nb;k++) ret += B[k] * uk[k]; for(int k = 0;k < na;k++) ret -= A[k] * yk[k]; for(int k = na;k > 1;k--) yk[k-1] = yk[k-2]; yk[0] = ret; return (float)ret; }