kicad/pcb_calculator/transline/twistedpair.cpp

186 lines
5.4 KiB
C++

/*
* twistedpair.h - twisted pair class definition
*
* Copyright (C) 2011 Michael Margraf <michael.margraf@alumni.tu-berlin.de>
* Modifications 2011 for Kicad: Jean-Pierre Charras
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or (at
* your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this package; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
* Boston, MA 02110-1301, USA.
*
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <cmath>
#include <units.h>
#include <transline.h>
#include <twistedpair.h>
TWISTEDPAIR::TWISTEDPAIR() : TRANSLINE()
{
m_Name = "TwistedPair";
// Initialize these variables mainly to avoid warnings from a static analyzer
din = 0.0; // Inner diameter of conductor
dout = 0.0; // Outer diameter of insulator
twists = 0.0; // Twists per length
er_env = 0.0; // dielectric constant of environment*/
len = 0.0; // Length of cable
Z0 = 0.0; // characteristic impedance
ang_l = 0.0; // Electrical length in angle
atten_dielectric = 0.0; // Loss in dielectric (dB)
atten_cond = 0.0; // Loss in conductors (dB)
er_eff = 1.0; // Effective dielectric constant
}
// -------------------------------------------------------------------
void TWISTEDPAIR::getProperties()
{
m_freq = getProperty( FREQUENCY_PRM );
din = getProperty( PHYS_DIAM_IN_PRM );
dout = getProperty( PHYS_DIAM_OUT_PRM );
len = getProperty( PHYS_LEN_PRM );
er = getProperty( EPSILONR_PRM );
m_murC = getProperty( MURC_PRM );
m_tand = getProperty( TAND_PRM );
m_sigma = 1.0 / getProperty( RHO_PRM );
twists = getProperty( TWISTEDPAIR_TWIST_PRM );
er_env = getProperty( TWISTEDPAIR_EPSILONR_ENV_PRM );
Z0 = getProperty( Z0_PRM );
ang_l = getProperty( ANG_L_PRM );
}
// -------------------------------------------------------------------
void TWISTEDPAIR::calc()
{
m_skindepth = skin_depth();
double tw = atan( twists * M_PI * dout ); // pitch angle
er_eff = er_env + (0.25 + 0.0007 * tw * tw) * (er - er_env);
Z0 = ZF0 / M_PI / sqrt( er_eff ) * acosh( dout / din );
atten_cond = 10.0 / log( 10.0 ) * len / m_skindepth / m_sigma / M_PI / Z0 / (din - m_skindepth);
atten_dielectric = 20.0 / log( 10.0 ) * len * M_PI / C0* m_freq * sqrt( er_eff ) * m_tand;
ang_l = 2.0* M_PI* len* sqrt( er_eff ) * m_freq / C0; // in radians
}
// -------------------------------------------------------------------
void TWISTEDPAIR::show_results()
{
setProperty( Z0_PRM, Z0 );
setProperty( ANG_L_PRM, ang_l );
setResult( 0, er_eff, "" );
setResult( 1, atten_cond, "dB" );
setResult( 2, atten_dielectric, "dB" );
setResult( 3, m_skindepth / UNIT_MICRON, "µm" );
}
// -------------------------------------------------------------------
void TWISTEDPAIR::analyze()
{
getProperties();
calc();
show_results();
}
#define MAX_ERROR 0.000001
// -------------------------------------------------------------------
void TWISTEDPAIR::synthesize()
{
double Z0_dest, Z0_current, Z0_result, increment, slope, error;
int iteration;
getProperties();
/* required value of Z0 */
Z0_dest = Z0;
/* Newton's method */
iteration = 0;
/* compute parameters */
calc();
Z0_current = Z0;
error = fabs( Z0_dest - Z0_current );
while( error > MAX_ERROR )
{
iteration++;
if( isSelected( PHYS_DIAM_IN_PRM ) )
{
increment = din / 100.0;
din += increment;
}
else
{
increment = dout / 100.0;
dout += increment;
}
/* compute parameters */
calc();
Z0_result = Z0;
/* f(w(n)) = Z0 - Z0(w(n)) */
/* f'(w(n)) = -f'(Z0(w(n))) */
/* f'(Z0(w(n))) = (Z0(w(n)) - Z0(w(n+delw))/delw */
/* w(n+1) = w(n) - f(w(n))/f'(w(n)) */
slope = (Z0_result - Z0_current) / increment;
slope = (Z0_dest - Z0_current) / slope - increment;
if( isSelected( PHYS_DIAM_IN_PRM ) )
din += slope;
else
dout += slope;
if( din <= 0.0 )
din = increment;
if( dout <= 0.0 )
dout = increment;
/* find new error */
/* compute parameters */
calc();
Z0_current = Z0;
error = fabs( Z0_dest - Z0_current );
if( iteration > 100 )
break;
}
setProperty( PHYS_DIAM_IN_PRM, din );
setProperty( PHYS_DIAM_OUT_PRM, dout );
/* calculate physical length */
ang_l = getProperty( ANG_L_PRM );
len = C0 / m_freq / sqrt( er_eff ) * ang_l / 2.0 / M_PI; /* in m */
setProperty( PHYS_LEN_PRM, len );
/* compute parameters */
calc();
/* print results in the subwindow */
show_results();
}