Ruprecht Altenburger / Library_Misc_cuboid

branch for cuboid

IIR_filter.cpp@0:72b60c5271cc, 2019-03-07 (annotated)

Committer:
altb2
Date:
Thu Mar 07 07:03:44 2019 +0000
Revision:
0:72b60c5271cc
Child:
2:8706bb4e8f93
System running

Who changed what in which revision?

UserRevisionLine numberNew contents of line
altb2 0:72b60c5271cc 1 #include "IIR_filter.h"
altb2 0:72b60c5271cc 2 #include "mbed.h"
altb2 0:72b60c5271cc 3 using namespace std;
altb2 0:72b60c5271cc 4
altb2 0:72b60c5271cc 5 /*
altb2 0:72b60c5271cc 6 IIR filter implemention for the following filter types:
altb2 0:72b60c5271cc 7 init for: first order differentiatior: G(s) = s/(T*s + 1)
altb2 0:72b60c5271cc 8 first order lowpass with gain G(s) = K/(T*s + 1)
altb2 0:72b60c5271cc 9 second order lowpass with gain G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0*w0)
altb2 0:72b60c5271cc 10 nth order, with arbitrary values
altb2 0:72b60c5271cc 11 the billinear transformation is used for s -> z
altb2 0:72b60c5271cc 12 reseting the filter only makes sence for static signals, whatch out if you're using the differnetiator
altb2 0:72b60c5271cc 13 */
altb2 0:72b60c5271cc 14
altb2 0:72b60c5271cc 15 // G(s) = s/(T*s + 1)
altb2 0:72b60c5271cc 16 IIR_filter::IIR_filter(float T, float Ts){
altb2 0:72b60c5271cc 17
altb2 0:72b60c5271cc 18 // filter orders
altb2 0:72b60c5271cc 19 nb = 1; // Filter Order
altb2 0:72b60c5271cc 20 na = 1; // Filter Order
altb2 0:72b60c5271cc 21
altb2 0:72b60c5271cc 22 // filter coefficients
altb2 0:72b60c5271cc 23 B = (double*)malloc((nb+1)*sizeof(double));
altb2 0:72b60c5271cc 24 A = (double*)malloc(na*sizeof(double));
altb2 0:72b60c5271cc 25 B[0] = 2.0/(2.0*(double)T + (double)Ts);
altb2 0:72b60c5271cc 26 B[1] = -B[0];
altb2 0:72b60c5271cc 27 A[0] = -(2.0*(double)T - (double)Ts)/(2.0*(double)T + (double)Ts);
altb2 0:72b60c5271cc 28
altb2 0:72b60c5271cc 29 // signal arrays
altb2 0:72b60c5271cc 30 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 0:72b60c5271cc 31 yk = (double*)malloc(na*sizeof(double));
altb2 0:72b60c5271cc 32 uk[0]= uk[1] = 0.0;
altb2 0:72b60c5271cc 33 yk[0] = 0.0;
altb2 0:72b60c5271cc 34
altb2 0:72b60c5271cc 35 // dc-gain
altb2 0:72b60c5271cc 36 this->K = 0.0;
altb2 0:72b60c5271cc 37 }
altb2 0:72b60c5271cc 38
altb2 0:72b60c5271cc 39 // G(s) = K/(T*s + 1)
altb2 0:72b60c5271cc 40 IIR_filter::IIR_filter(float T, float Ts, float K){
altb2 0:72b60c5271cc 41
altb2 0:72b60c5271cc 42 // filter orders
altb2 0:72b60c5271cc 43 nb = 1; // Filter Order
altb2 0:72b60c5271cc 44 na = 1; // Filter Order
altb2 0:72b60c5271cc 45
altb2 0:72b60c5271cc 46 // filter coefficients
altb2 0:72b60c5271cc 47 B = (double*)malloc((nb+1)*sizeof(double));
altb2 0:72b60c5271cc 48 A = (double*)malloc(na*sizeof(double));
altb2 0:72b60c5271cc 49 B[0] = (double)Ts/((double)Ts + 2.0*(double)T);
altb2 0:72b60c5271cc 50 B[1] = B[0];
altb2 0:72b60c5271cc 51 A[0] = ((double)Ts - 2.0*(double)T)/((double)Ts + 2.0*(double)T);
altb2 0:72b60c5271cc 52
altb2 0:72b60c5271cc 53 // signal arrays
altb2 0:72b60c5271cc 54 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 0:72b60c5271cc 55 yk = (double*)malloc(na*sizeof(double));
altb2 0:72b60c5271cc 56 uk[0]= uk[1] = 0.0;
altb2 0:72b60c5271cc 57 yk[0] = 0.0;
altb2 0:72b60c5271cc 58
altb2 0:72b60c5271cc 59 // dc-gain
altb2 0:72b60c5271cc 60 this->K = (double)K;
altb2 0:72b60c5271cc 61 }
altb2 0:72b60c5271cc 62
altb2 0:72b60c5271cc 63 // G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0^2)
altb2 0:72b60c5271cc 64 IIR_filter::IIR_filter(float w0, float D, float Ts, float K){
altb2 0:72b60c5271cc 65
altb2 0:72b60c5271cc 66 // filter orders
altb2 0:72b60c5271cc 67 nb = 2; // Filter Order
altb2 0:72b60c5271cc 68 na = 2; // Filter Order
altb2 0:72b60c5271cc 69
altb2 0:72b60c5271cc 70 // filter coefficients
altb2 0:72b60c5271cc 71 B = (double*)malloc((nb+1)*sizeof(double));
altb2 0:72b60c5271cc 72 A = (double*)malloc(na*sizeof(double));
altb2 0:72b60c5271cc 73 double k0 = (double)Ts*(double)Ts*(double)w0*(double)w0;
altb2 0:72b60c5271cc 74 double k1 = 4.0*(double)D*(double)Ts*(double)w0;
altb2 0:72b60c5271cc 75 double k2 = k0 + k1 + 4.0;
altb2 0:72b60c5271cc 76 B[0] = (double)K*k0/k2;
altb2 0:72b60c5271cc 77 B[1] = 2.0*B[0];
altb2 0:72b60c5271cc 78 B[2] = B[0];
altb2 0:72b60c5271cc 79 A[0] = (2.0*k0 - 8.0)/k2;
altb2 0:72b60c5271cc 80 A[1] = (k0 - k1 + 4.0)/k2;
altb2 0:72b60c5271cc 81
altb2 0:72b60c5271cc 82 // signal arrays
altb2 0:72b60c5271cc 83 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 0:72b60c5271cc 84 yk = (double*)malloc(na*sizeof(double));
altb2 0:72b60c5271cc 85 uk[0]= uk[1] = uk[2] = 0.0;
altb2 0:72b60c5271cc 86 yk[0] = yk[1] = 0.0;
altb2 0:72b60c5271cc 87
altb2 0:72b60c5271cc 88 // dc-gain
altb2 0:72b60c5271cc 89 this->K = (double)K;
altb2 0:72b60c5271cc 90 }
altb2 0:72b60c5271cc 91
altb2 0:72b60c5271cc 92 IIR_filter::IIR_filter(float *b, float *a, int nb_, int na_){
altb2 0:72b60c5271cc 93
altb2 0:72b60c5271cc 94 // filter orders
altb2 0:72b60c5271cc 95 this->nb = nb_-1; // Filter Order
altb2 0:72b60c5271cc 96 this->na = na_; // Filter Order
altb2 0:72b60c5271cc 97
altb2 0:72b60c5271cc 98 // filter coefficients
altb2 0:72b60c5271cc 99 B = (double*)malloc((nb+1)*sizeof(double));
altb2 0:72b60c5271cc 100 A = (double*)malloc(na*sizeof(double));
altb2 0:72b60c5271cc 101 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 0:72b60c5271cc 102 yk = (double*)malloc(na*sizeof(double));
altb2 0:72b60c5271cc 103
altb2 0:72b60c5271cc 104 for(int k=0;k<=nb;k++){
altb2 0:72b60c5271cc 105 B[k]=b[k];
altb2 0:72b60c5271cc 106 uk[k]=0.0;
altb2 0:72b60c5271cc 107 }
altb2 0:72b60c5271cc 108 for(int k=0;k<na;k++){
altb2 0:72b60c5271cc 109 A[k] = a[k];
altb2 0:72b60c5271cc 110 yk[k] = 0.0;
altb2 0:72b60c5271cc 111 }
altb2 0:72b60c5271cc 112
altb2 0:72b60c5271cc 113 // dc-gain
altb2 0:72b60c5271cc 114 this->K = 1.0;
altb2 0:72b60c5271cc 115 }
altb2 0:72b60c5271cc 116
altb2 0:72b60c5271cc 117
altb2 0:72b60c5271cc 118 IIR_filter::~IIR_filter() {}
altb2 0:72b60c5271cc 119
altb2 0:72b60c5271cc 120 void IIR_filter::reset(float val) {
altb2 0:72b60c5271cc 121 for(int k=0;k < nb;k++)
altb2 0:72b60c5271cc 122 uk[k] = (double)val;
altb2 0:72b60c5271cc 123 for(int k=0;k < na;k++)
altb2 0:72b60c5271cc 124 yk[k] = (double)val*K;
altb2 0:72b60c5271cc 125
altb2 0:72b60c5271cc 126 }
altb2 0:72b60c5271cc 127
altb2 0:72b60c5271cc 128 /*
altb2 0:72b60c5271cc 129 the filter is operating as follows:
altb2 0:72b60c5271cc 130 (B[0] + B[1]*z^-1 + ... + B[nb]*z^-nb)*U(z) = (1 + A[0]*z^-1 + ... + A[na-1]*z^-na))*Y(z)
altb2 0:72b60c5271cc 131 y(n) = B[0]*u(k) + B[1]*u(k-1) + ... + B[nb]*u(k-nb) + ...
altb2 0:72b60c5271cc 132 - A[0]*y(k-1) - A[1]*y(k-2) - ... - A[na]*y(n-na)
altb2 0:72b60c5271cc 133 */
altb2 0:72b60c5271cc 134 float IIR_filter::filter(double input){
altb2 0:72b60c5271cc 135 for(int k = nb;k > 0;k--) // shift input values back
altb2 0:72b60c5271cc 136 uk[k] = uk[k-1];
altb2 0:72b60c5271cc 137 uk[0] = input;
altb2 0:72b60c5271cc 138 double ret = 0.0;
altb2 0:72b60c5271cc 139 for(int k = 0;k <= nb;k++)
altb2 0:72b60c5271cc 140 ret += B[k] * uk[k];
altb2 0:72b60c5271cc 141 for(int k = 0;k < na;k++)
altb2 0:72b60c5271cc 142 ret -= A[k] * yk[k];
altb2 0:72b60c5271cc 143 for(int k = na;k > 1;k--)
altb2 0:72b60c5271cc 144 yk[k-1] = yk[k-2];
altb2 0:72b60c5271cc 145 yk[0] = ret;
altb2 0:72b60c5271cc 146 return (float)ret;
altb2 0:72b60c5271cc 147 }
altb2 0:72b60c5271cc 148