% gain4647.m - compute gain and phase for Figures 4.6 and 4.7, p. 179 H&H
% HJSIII - 96.10.17

% component values
R = 100e3;
C = 0.1E-6;
R1 = 2e3;
R2 = 18e3;
C1 = 4.7e-6;

% use 0.01 Hz <= f <= 1 MHz
for i=1:81,
  lf = (i-21) / 10;
  f = 10 ^ lf;

% impedances
  ZR = R;
  ZC = -j / ( 2 * pi * f * C );
  ZR1 = R1;
  ZR2 = R2;
  ZC1 = -j / ( 2 * pi * f * C1 );

% Fig. 4.6 - see also p. 35 H&H
  K = 1 + R2/R1;
  G46 = K * ZR / ( ZC + ZR );

% Fig. 4.7
  G47 = 1 + ZR2 / ( ZR1 + ZC1 );

% save log of gain and phase in degrees
  lg46 = log10( abs( G46 ) );
  phi46 = angle( G46 ) * 180 / pi;
  lg47 = log10( abs( G47 ) );
  phi47 = angle( G47 ) * 180 / pi;
  keep(i,:) = [ lf lg46 phi46 lg47 phi47 ];
end

% plot
subplot(2,1,1)
  plot( keep(:,1),keep(:,2), keep(:,1),keep(:,4),'--')
  title('Gain for Figures 4.6 (solid) and 4.7 (dash), p. 179 H&H')
  xlabel('log f')
  ylabel('log G')
subplot(2,1,2)
  plot( keep(:,1),keep(:,3), keep(:,1),keep(:,5),'--')
  xlabel('log f')
  ylabel('phase G (deg)')