%
% filter1
%
source([0 0],'V','v'); 
%plot([0 0],[0 -1],'k','linewidth',1.5)
ground([0 -3.6],'')

resist([0 0],'h','R_1','y_1')
plot([3.6 7.2],[0 0],'k','linewidth',1.5)

cap([3.6 0],'v','C_1','y_2')
ground([3.6 -3.6],'')
plot([6 7.2],[-2 -2],'k','linewidth',1.5)
plot([6 6],[-2 -4],'k','linewidth',1.5)
resist([7 -4],'h','R_3','y_4')
text(6.1,-3.5,'x_1')
text(4,0.5,'x_1')
text(11, -3.5,'x_2')
plot([6 7],[-4 -4],'k','linewidth',1.5)
resist([6 -4],'v','R_2','y_3')
ground([6 -7.6],'')
opamp([7.2 1],4,0)

plot([11.2 12 12 10.6],[-1 -1 -4 -4],'k','linewidth',1.5)

axis off
hold off
return

resist([3.5 -5],'h','R_2','y_2')
plot([2.5 2.5],[-2.5 -5],'k','linewidth',1.5)
plot([2.5 4],[-5 -5],'k','linewidth',1.5)
plot([6.9 8.5],[-5 -5],'k','linewidth',1.5)
plot([8.5 8.5],[-5 -1.5],'k','linewidth',1.5)
plot([7.5 8.5],[-1.5 -1.5],'k','linewidth',1.5)
text(2.4,-2,'x_1','fontsize',20)
text(7.8,-2,'x_2','fontsize',20)
hold off
axis off