MATLAB: Create X-axis limit

Question

Hi all,

I have a plot created from the following code

 close all
 gm = 1e-6:1e-3:1;
 grid on
 hold on
 %Rd = 1K
 einv = 2.*sqrt((4e-9)^2+(4.*1.38e-23.*298.15.*1e3))
 plot(gm,einv./(gm*1e3),'color',[0,0,0]); 
 %Rd = 10K
 einv = 2.*sqrt((4e-9)^2+(4.*1.38e-23*298.15*10e3))
 plot(gm,einv./(gm*10e3),'color',[0.25,0.25,0.25]);
 %Rd = 100K
 einv = 2.*sqrt((4e-9)^2+(4.*1.38e-23*298.15*100e3))
 plot(gm,einv./(gm*100e3),'color',[0.5,0.5,0.5]);
 %Rd = 1M
 einv = 2.*sqrt((4e-9)^2+(4.*1.38e-23*298.15*1e6))
 plot(gm,einv./(gm*1e6),'color',[0.75,0.75,0.75]);
 xlabel ('gm (S)'); ylabel ( 'EINV_{min} (V/sqrt(Hz))');
 set(gca,'xscale','log')
 set(gca,'yscale','log')
 legend('1K\Omega','10K\Omega','100K\Omega','1M\Omega');
 %print('einv','-dpng')

Which yields the following

However, I want to implement a limit on the y-axis at 5e-9. I would like the plot to not just chop off the data below 5e-9 but rather to create a limit so that the plots asymptote towards this value. Something like this (Sorry for the crude drawing, though this is just to help get the idea across…)

Can this be done? If so, would anybody be so kind to show me how I can achieve this?

Thank you in advance.

Answer 1

How about if you just add 5e-9 to all numbers:

close all
gm = 1e-6:1e-3:1;
grid on
hold on
%Rd = 1K
einv = 2.*sqrt((4e-9)^2+(4.*1.38e-23.*298.15.*1e3))
einv = einv./(gm*1e3) + 5e-9;
plot(gm,einv,'color',[0,0,0], 'LineWidth', 2);
%Rd = 10K
einv = 2.*sqrt((4e-9)^2+(4.*1.38e-23*298.15*10e3))
einv = einv./(gm*10e3) + 5e-9;
plot(gm,einv,'color',[0.25,0.25,0.25], 'LineWidth', 2);
%Rd = 100K
einv = 2.*sqrt((4e-9)^2+(4.*1.38e-23*298.15*100e3))
einv = einv./(gm*100e3) + 5e-9;
plot(gm,einv,'color',[0.5,0.5,0.5], 'LineWidth', 2);
%Rd = 1M
einv = 2.*sqrt((4e-9)^2+(4.*1.38e-23*298.15*1e6))
einv = einv./(gm*1e6) + 5e-9;
plot(gm,einv,'color',[0.75,0.75,0.75], 'LineWidth', 2);
xlabel ('gm (S)'); ylabel ( 'EINV_{min} (V/sqrt(Hz))');
set(gca,'xscale','log')
set(gca,'yscale','log')
legend('1K\Omega','10K\Omega','100K\Omega','1M\Omega');
%print('einv','-dpng')

Looks fairly good to me.