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IIR_filter.cpp@18:f844dbc8ea87, 2019-03-06 (annotated)

Committer:
altb2
Date:
Wed Mar 06 15:23:27 2019 +0000
Revision:
18:f844dbc8ea87
deleted libs

Who changed what in which revision?

UserRevisionLine numberNew contents of line
altb2 18:f844dbc8ea87 1 #include "IIR_filter.h"
altb2 18:f844dbc8ea87 2 #include "mbed.h"
altb2 18:f844dbc8ea87 3 using namespace std;
altb2 18:f844dbc8ea87 4
altb2 18:f844dbc8ea87 5 /*
altb2 18:f844dbc8ea87 6 IIR filter implemention for the following filter types:
altb2 18:f844dbc8ea87 7 init for: first order differentiatior: G(s) = s/(T*s + 1)
altb2 18:f844dbc8ea87 8 first order lowpass with gain G(s) = K/(T*s + 1)
altb2 18:f844dbc8ea87 9 second order lowpass with gain G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0*w0)
altb2 18:f844dbc8ea87 10 nth order, with arbitrary values
altb2 18:f844dbc8ea87 11 the billinear transformation is used for s -> z
altb2 18:f844dbc8ea87 12 reseting the filter only makes sence for static signals, whatch out if you're using the differnetiator
altb2 18:f844dbc8ea87 13 */
altb2 18:f844dbc8ea87 14
altb2 18:f844dbc8ea87 15 // G(s) = s/(T*s + 1)
altb2 18:f844dbc8ea87 16 IIR_filter::IIR_filter(float T, float Ts){
altb2 18:f844dbc8ea87 17
altb2 18:f844dbc8ea87 18 // filter orders
altb2 18:f844dbc8ea87 19 nb = 1; // Filter Order
altb2 18:f844dbc8ea87 20 na = 1; // Filter Order
altb2 18:f844dbc8ea87 21
altb2 18:f844dbc8ea87 22 // filter coefficients
altb2 18:f844dbc8ea87 23 B = (double*)malloc((nb+1)*sizeof(double));
altb2 18:f844dbc8ea87 24 A = (double*)malloc(na*sizeof(double));
altb2 18:f844dbc8ea87 25 B[0] = 2.0/(2.0*(double)T + (double)Ts);
altb2 18:f844dbc8ea87 26 B[1] = -B[0];
altb2 18:f844dbc8ea87 27 A[0] = -(2.0*(double)T - (double)Ts)/(2.0*(double)T + (double)Ts);
altb2 18:f844dbc8ea87 28
altb2 18:f844dbc8ea87 29 // signal arrays
altb2 18:f844dbc8ea87 30 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 18:f844dbc8ea87 31 yk = (double*)malloc(na*sizeof(double));
altb2 18:f844dbc8ea87 32 uk[0]= uk[1] = 0.0;
altb2 18:f844dbc8ea87 33 yk[0] = 0.0;
altb2 18:f844dbc8ea87 34
altb2 18:f844dbc8ea87 35 // dc-gain
altb2 18:f844dbc8ea87 36 this->K = 0.0;
altb2 18:f844dbc8ea87 37 }
altb2 18:f844dbc8ea87 38
altb2 18:f844dbc8ea87 39 // G(s) = K/(T*s + 1)
altb2 18:f844dbc8ea87 40 IIR_filter::IIR_filter(float T, float Ts, float K){
altb2 18:f844dbc8ea87 41
altb2 18:f844dbc8ea87 42 // filter orders
altb2 18:f844dbc8ea87 43 nb = 1; // Filter Order
altb2 18:f844dbc8ea87 44 na = 1; // Filter Order
altb2 18:f844dbc8ea87 45
altb2 18:f844dbc8ea87 46 // filter coefficients
altb2 18:f844dbc8ea87 47 B = (double*)malloc((nb+1)*sizeof(double));
altb2 18:f844dbc8ea87 48 A = (double*)malloc(na*sizeof(double));
altb2 18:f844dbc8ea87 49 B[0] = (double)Ts/((double)Ts + 2.0*(double)T);
altb2 18:f844dbc8ea87 50 B[1] = B[0];
altb2 18:f844dbc8ea87 51 A[0] = ((double)Ts - 2.0*(double)T)/((double)Ts + 2.0*(double)T);
altb2 18:f844dbc8ea87 52
altb2 18:f844dbc8ea87 53 // signal arrays
altb2 18:f844dbc8ea87 54 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 18:f844dbc8ea87 55 yk = (double*)malloc(na*sizeof(double));
altb2 18:f844dbc8ea87 56 uk[0]= uk[1] = 0.0;
altb2 18:f844dbc8ea87 57 yk[0] = 0.0;
altb2 18:f844dbc8ea87 58
altb2 18:f844dbc8ea87 59 // dc-gain
altb2 18:f844dbc8ea87 60 this->K = (double)K;
altb2 18:f844dbc8ea87 61 }
altb2 18:f844dbc8ea87 62
altb2 18:f844dbc8ea87 63 // G(s) = K*w0^2/(s^2 + 2*D*w0*s + w0^2)
altb2 18:f844dbc8ea87 64 IIR_filter::IIR_filter(float w0, float D, float Ts, float K){
altb2 18:f844dbc8ea87 65
altb2 18:f844dbc8ea87 66 // filter orders
altb2 18:f844dbc8ea87 67 nb = 2; // Filter Order
altb2 18:f844dbc8ea87 68 na = 2; // Filter Order
altb2 18:f844dbc8ea87 69
altb2 18:f844dbc8ea87 70 // filter coefficients
altb2 18:f844dbc8ea87 71 B = (double*)malloc((nb+1)*sizeof(double));
altb2 18:f844dbc8ea87 72 A = (double*)malloc(na*sizeof(double));
altb2 18:f844dbc8ea87 73 double k0 = (double)Ts*(double)Ts*(double)w0*(double)w0;
altb2 18:f844dbc8ea87 74 double k1 = 4.0*(double)D*(double)Ts*(double)w0;
altb2 18:f844dbc8ea87 75 double k2 = k0 + k1 + 4.0;
altb2 18:f844dbc8ea87 76 B[0] = (double)K*k0/k2;
altb2 18:f844dbc8ea87 77 B[1] = 2.0*B[0];
altb2 18:f844dbc8ea87 78 B[2] = B[0];
altb2 18:f844dbc8ea87 79 A[0] = (2.0*k0 - 8.0)/k2;
altb2 18:f844dbc8ea87 80 A[1] = (k0 - k1 + 4.0)/k2;
altb2 18:f844dbc8ea87 81
altb2 18:f844dbc8ea87 82 // signal arrays
altb2 18:f844dbc8ea87 83 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 18:f844dbc8ea87 84 yk = (double*)malloc(na*sizeof(double));
altb2 18:f844dbc8ea87 85 uk[0]= uk[1] = uk[2] = 0.0;
altb2 18:f844dbc8ea87 86 yk[0] = yk[1] = 0.0;
altb2 18:f844dbc8ea87 87
altb2 18:f844dbc8ea87 88 // dc-gain
altb2 18:f844dbc8ea87 89 this->K = (double)K;
altb2 18:f844dbc8ea87 90 }
altb2 18:f844dbc8ea87 91
altb2 18:f844dbc8ea87 92 IIR_filter::IIR_filter(float *b, float *a, int nb_, int na_){
altb2 18:f844dbc8ea87 93
altb2 18:f844dbc8ea87 94 // filter orders
altb2 18:f844dbc8ea87 95 this->nb = nb_-1; // Filter Order
altb2 18:f844dbc8ea87 96 this->na = na_; // Filter Order
altb2 18:f844dbc8ea87 97
altb2 18:f844dbc8ea87 98 // filter coefficients
altb2 18:f844dbc8ea87 99 B = (double*)malloc((nb+1)*sizeof(double));
altb2 18:f844dbc8ea87 100 A = (double*)malloc(na*sizeof(double));
altb2 18:f844dbc8ea87 101 uk = (double*)malloc((nb+1)*sizeof(double));
altb2 18:f844dbc8ea87 102 yk = (double*)malloc(na*sizeof(double));
altb2 18:f844dbc8ea87 103
altb2 18:f844dbc8ea87 104 for(int k=0;k<=nb;k++){
altb2 18:f844dbc8ea87 105 B[k]=b[k];
altb2 18:f844dbc8ea87 106 uk[k]=0.0;
altb2 18:f844dbc8ea87 107 }
altb2 18:f844dbc8ea87 108 for(int k=0;k<na;k++){
altb2 18:f844dbc8ea87 109 A[k] = a[k];
altb2 18:f844dbc8ea87 110 yk[k] = 0.0;
altb2 18:f844dbc8ea87 111 }
altb2 18:f844dbc8ea87 112
altb2 18:f844dbc8ea87 113 // dc-gain
altb2 18:f844dbc8ea87 114 this->K = 1.0;
altb2 18:f844dbc8ea87 115 }
altb2 18:f844dbc8ea87 116
altb2 18:f844dbc8ea87 117
altb2 18:f844dbc8ea87 118 IIR_filter::~IIR_filter() {}
altb2 18:f844dbc8ea87 119
altb2 18:f844dbc8ea87 120 void IIR_filter::reset(float val) {
altb2 18:f844dbc8ea87 121 for(int k=0;k < nb;k++)
altb2 18:f844dbc8ea87 122 uk[k] = (double)val;
altb2 18:f844dbc8ea87 123 for(int k=0;k < na;k++)
altb2 18:f844dbc8ea87 124 yk[k] = (double)val*K;
altb2 18:f844dbc8ea87 125
altb2 18:f844dbc8ea87 126 }
altb2 18:f844dbc8ea87 127
altb2 18:f844dbc8ea87 128 /*
altb2 18:f844dbc8ea87 129 the filter is operating as follows:
altb2 18:f844dbc8ea87 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 18:f844dbc8ea87 131 y(n) = B[0]*u(k) + B[1]*u(k-1) + ... + B[nb]*u(k-nb) + ...
altb2 18:f844dbc8ea87 132 - A[0]*y(k-1) - A[1]*y(k-2) - ... - A[na]*y(n-na)
altb2 18:f844dbc8ea87 133 */
altb2 18:f844dbc8ea87 134 float IIR_filter::filter(double input){
altb2 18:f844dbc8ea87 135 for(int k = nb;k > 0;k--) // shift input values back
altb2 18:f844dbc8ea87 136 uk[k] = uk[k-1];
altb2 18:f844dbc8ea87 137 uk[0] = input;
altb2 18:f844dbc8ea87 138 double ret = 0.0;
altb2 18:f844dbc8ea87 139 for(int k = 0;k <= nb;k++)
altb2 18:f844dbc8ea87 140 ret += B[k] * uk[k];
altb2 18:f844dbc8ea87 141 for(int k = 0;k < na;k++)
altb2 18:f844dbc8ea87 142 ret -= A[k] * yk[k];
altb2 18:f844dbc8ea87 143 for(int k = na;k > 1;k--)
altb2 18:f844dbc8ea87 144 yk[k-1] = yk[k-2];
altb2 18:f844dbc8ea87 145 yk[0] = ret;
altb2 18:f844dbc8ea87 146 return (float)ret;
altb2 18:f844dbc8ea87 147 }