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//define problem parameters
TT=500e-12; // transit time
T0=300; //temperature
Is0=5e-15; // reverse saturation current at 300K
Rs=1.5; // series resistance
nn=1.16; //emission coefficient
// parameters needed to describe temperature behavior of
// the band-gap energy in Si
alpha=7.02e-4;
beta=1108;
Wg0=1.16;
pt=3;
// quiescent current
Iq=50e-3;
// frequency range 10MHz to 1GHz
f_min=10e6; // lower limit
f_max=1e9; //upper limit
N=300; // number of points in the graph
f=f_min*((f_max/f_min).^((0:N)/N)); // compute frequency points on log scale
// temperatures for which analysis will be performed
T_points=[250 300 350 400];
// define physical constants
q=1.60218e-19; // electron charge
k=1.38066e-23; // Boltzmann's constant
for n=1:length(T_points)
T=T_points(n);
s=sprintf('T=%.f\n',T);
Vt=k*T/q;
Wg=Wg0-alpha*T^2/(beta+T);
s=sprintf('%s Wg(T)=%f\n',s,Wg);
Is=Is0*(T/T0)^(pt/nn)*exp(-Wg/Vt*(1-T/T0));
s=sprintf('%s Is(T)=%e\n',s,Is);
Vq=nn*Vt*log(1+Iq/Is);
s=sprintf('%s Vq(T)=%f\n',s,Vq);
Rd=nn*Vt/Iq;
s=sprintf('%s Rd(T)=%f\n',s,Rd);
Cd=Is*TT/nn/Vt*exp(Vq/nn/Vt);
s=sprintf('%s Cd(T)=%fpF\n',s,Cd/1e-12)
Zc=1./(%i*2*%pi*f*Cd);
Zin=Rs+Rd*Zc./(Rd+Zc);
plot(f/1e6,abs(Zin));
set(gca(),"auto_clear","off");
end;
title('Frequency behavior of small-signal diode model');
xlabel('Frequency {\itf}, MHz');
ylabel('Impedance |Z|, \Omega');
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