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# Fixed Step Size in Orcad Capture

Last post Thu, Aug 8 2013 9:07 AM by Jothi86. 2 replies.
 Started by Jothi86 07 Aug 2013 10:45 PM. Topic has 2 replies and 2434 views
• #### Wed, Aug 7 2013 10:45 PM

• Jothi86
• Joined on Wed, Aug 7 2013
• Posts 2
• Points 25
Fixed Step Size in Orcad Capture
 Dear designers, I have to add noise to my circuit analysis. Since, Pspice do not have the noise source, I have used  "VPWL_F_RE_FOREVER". In this i have given a input data file containg the data of gaussian white noise generated  using matlab. Now the problem is,I have a data with equally spaced step size. say for example 1ms. I set "Start saving data=0, TSTOP=20m,maximum step size=1m" .While the simulation, the psice takes nonuniform step size for the simulation. In this situation, suppose if i have the noise data for 0m, 1m,2m and so on... Between the two succesive time step the pspice generates few new steps as its own. But I strictly need the simulation with the time step used in the input data file. Can any one please help me in this regard? Cheers, Jothi
• Post Points: 20
• #### Thu, Aug 8 2013 12:51 AM

• oldmouldy
• Joined on Tue, Jul 15 2008
• Woking, Surrey
• Posts 1,391
• Points 23,705
Re: Fixed Step Size in Orcad Capture
 SPICE simulators use an internal algorithm to determine the Minimum Step Size, this cannot be determined by simulator settings. Whilst your input data may have fixed time interval data points, linear interpolation will be used between those points so your input wlll be changing, the circuit state will be changing and PSpice will run the simulation to evaluate the effect of those changes.
• Post Points: 20
• #### Thu, Aug 8 2013 9:07 AM

• Jothi86
• Joined on Wed, Aug 7 2013
• Posts 2
• Points 25
Re: Fixed Step Size in Orcad Capture
 Dear Sir, I accept your point. But one thing is not clear for me. Since we have to study the effect of noise on a particular circuit, we should have to add a noise data to each iteration. Right? If so then how to do it in orcad?Regards,Jothi
• Post Points: 5