Question about changing max. step size in Orcad

[Abu Ammora]

Max. Step size in orcad

I'm designing FSk TX on Orcad Capture , Is it better to increase the Max step size or decrease it ( I mean in Transient Analysis ) , as when i change the values i found that some values in freq. Domain changed , I want to make A REAL simulation for the circuit that become very near to the practical results after implementation , Does anyone have ideas ?

Thanks . . .

 

[flatulent]

Re: Max. Step size in orcad

Making the step size smaller will give you more accurate results. Try 1/10 of the fastest rise or fall time of any waveform in the circuit. You can also reduce the tolerance limits in the .option statement.

Both of the above will slow the simulation. Getting the wrong results sooner is useless when you can get the right results later.

 

[Abu Ammora]

Re: Max. Step size in orcad

Getting the wrong results sooner is useless when you can get the right results later.

I really don't understand what u mean in this sentence

 

[flatulent]

Re: Max. Step size in orcad

It means that if you use large step sizes and loose tolerances the simulation will run faster and end earlier but with wrong results. Most simulator vendors make their specification sheets look good. Low simulation times is one parameter. They do this by making the default parameters loose.

 

[Abu Ammora]

Re: Max. Step size in orcad

Thanks

so , If my Design is sensitive ( the Change of values is critical ) , it's better to decrease the step size to obtain correct results but the simulation time will be increased , Isn't it ?

 

[flatulent]

Re: Max. Step size in orcad

Not only step size, but relative tolerance and absolute tolerance (these features can be found in the directions of the program and also after market books) This will make the FFT frequency domain plots more accurate.

 

[Abu Ammora]

Re: Max. Step size in orcad

Not only step size, but relative tolerance and absolute tolerance (.

Can u please tell me how can i find these feautures in orcad , from Which menu ?

thanks