How do you generate PCB for designs which needs to be simulated first

How do you take your simulated design to PCB?
Do you create another copy of same schematic and add up pcb only components like connectors etc?
Use same schematic and add PCB only components?

Looking for ideas on what works best in case where first simulation is done and then design taken to PCB.

My simulation software and PCB software are totally different. Also, I only simulate parts of the circuit where necessary. So the PCB design is a totally separate exercise.

Keith

If you are doing high speed signal integrity simulation using IBIS you need a basic placed PCB as a minimum so that the transmission line lengths can be approximated. If you are using spice simulation then you dont, they can be seperate software packages, and usually are.

Thank You, What about cases where you can simulate full (almost) circuit. What issue one may face while taking simulated design schematic to PCB layout? Example: DC-DC convertors and where I do simulate almost complete circuit.

I would sugest spice simulation of the circuit first, that is common practice.

Agree, but then how to I create PCB netlist? Should I use same schematic, the one used for SPICE simulation or should I create a copy of same? if I copy how do I manage to these two in sync?
From tool perspective what works best?

It varies, we can do it either way, create the schematic in our EDA system then transfer it to the spice package, or most engineers here sort of doodle bits of circuitry in spice, then cobble it together by manualy re-doing the schematic in the EDA package...

Many schematic tools have an option to extract SPICE netlists or even to schedule a simulation. For effective operation, you would also want to have a supplied library of simulation models and flexible simulation control. Cadence Orcad CIS is an example of a tool, that's basically capable of doing both simulation and PCB schematic entry without major restrictions. Also Altium Designer or Mentor Expedition are offering similar features.

But being able to perform a full circuit simulation doesn't necessarily mean that it's a reasonable design step. Some possible points against it:

- design is too complex. Setup of stimulation sources is long winded, simulation time is inacceptable.
- models are missing or known to be inappropriate respectively incorrect
- you're mainly interested in a functional simulation of specific circuit details
- design complexity suggests to replace circuit parts by simplified behavioral models
- parasitic PCB properties need to be reflected by additional circuit elements

Personally, I do rarely full circuit simulations and don't see a problem in setting up partial simulation schematics in a separate tool, e.g. LTSpice. But I don't want to discourage designers from trying full circuit simulation with integrated tools.

In some Edaboard posts, I hear an expectation, that full circuit simulation can help to understand a circuit which function would otherwise remain a mystery. The reported results don't approve the speculation in my view.

Thanks FvM, This help understand it better. Can you please clarify what do you mean by "- models are missing or known to be inappropriate respectively incorrect"

I have another related question: Assuming I am able to perform complete circuit simulation (my circuit is small, i have all necessary models etc). Now how should I deal with PCB only components like connectors? Should I place these in schematic or add these only in PCB layout tool?
What role connector play in schematics and in real life production environment?

You ideally want the schematic to match the PCB layout so you want to have the connectors on the schematic. I design for IC layout and the approach I take there is to put all components which aren't going to end up on the IC, e.g. external components and stimulus, in a separate block in the hierarchy. Then when it comes to generating the netlist for layout I can remove that block without risking unwanted changed to the real circuit. You could take the same approach - put the connectors in a separate block which you don't include for simulation.

Keith