Page 267 - Analog and Digital Filter Design

Analog and Digital Filter Design

Listing 9.1 is reproduced from Chapter 4, listing 4.1 of Digital Filter Designer's
Handbook by C. Britton Rorabaugh, 1993. Reproduced with permission from
McGraw-Hill.

/*****x******t**********r******t*** /
/* */
/* Listing 4.1 */
/* +/
/ * ChebyshevFreqResponse ) * /
(
/* */
/**********xtt********fxt***c******/
#include (math.h)
#define PI (double) 3.141592653589
void chebyshevFreqResponse( int order,
float ripple,
char normalizationType.
float frequency,
float *magnitude,
float *phase)
I
double A, gamma, epsilon, work;
double rp, ip, x, i, r, rpt, ipt;
double normalizedFrequency, hSubZero;
int k, ix;
epsilon = sqrt( -1.0 + pow( (double)lO.O, (double) (rippleil0.0) ));
gamma = pow( ( ( 1.0 + sqrt ( 1.0 + epsilon+epsilon) /epsilon),
(double) (l.O/(float) order) );
if ( nomLalizationType = '3' )
I
work = l.O/epsilon;
A = ( log( work + sqrt( work'work - 1.0) ) ) / order;
normalizedFrequency = frequency * ( exp(A) + exp(-A) ) /2.0;
1
else
I
normalizedFrequency = frequency;
}
rp = 1.0;
ip = 0.0;
for( k = 4; k< = order; k++)
1
x = (2*k - 1) * PI / (2.0*order);
i = 0.5 * (gamma + l.O/gamma) * cos(x);
r = -0.5 * (gamma - l.O/gamrr~a) * sin(x);
rpt = ip * i - rp * I;
ipt = -rp * i - r * ip;
ip = ipt;
rp = rpt;
I .
hsubzero = sqrt( ip*ip + rp*rp);
if( order%2 = 0 I
hsubzero = hSubZero / sqrt(l.0 + epsilon*epsilon);