PCB layout - board level simulation

[joniengr081]

We normally simulate electronics circuits using SPICE simulators. There are many simulators available for that purpose. One of them is LT SPICE by Analog Devices in which we can add/import 3rd party components in the library and simulate the circuit using their SPICE models.

I am wondering how do we simulate the layout to check the signal and power integrity in the PCB layout. The PCB stackup consist of multiple copper layers for routing signals and power distribution, and there are dielectric materials between the layers. FR4 is an example of dielectric material is widely used in PCB.

The signal quality in the PCB traces depend on the signal switching frequency, rise time, bandwidth and also mainly on the physical design of the layout and dielectric material. Although there are PCB layout design consideration for high speed signals but I am still wondering if there exist a tool which can simulate the transmission lines and is free to use that would be the best. Any suggestion on such simulators ?

[thinkfat]

I only know of OpenEMS as a free tool. It's an electromagnetic field solver and can be used for what you describe, but it's scary-complex. You more or less "program" your PCB with Python and/or matlab, and not only the PCB, but supply the mesh, the feed-in/out points, how to excite them, etc. I've tried using it for simple transmission line computations but it was so time consuming to set up a design that I stopped. It was simply beyond my skills.

[joniengr081]

I found some tools for example mentor graphics signal integrity tool and pcb saturn calculator. Has anyone tried them ? I guess the tool from mentor graphics is not free. I have not checked pcb saturn calculator but it look like a impedance calculator for a given stack up in PCB layout.

[Doctorandus_P]

https://en.wikipedia.org/wiki/Comparison_of_EM_simulation_software

[Feynman]

What you are describing is a 3D field solver. These are usually very expensive software tools from companies like Mentor Graphics, Ansys or Simbeor. The only free 3D field solver I'm aware of is openEMS. But with openEMS even for simulating simple PCB structures you will spend many, many hours until to get useful results...

The Saturn PCB Calculator is not a 3D Field Solver. It's fundamentally just a collection of approximation formulas.

It all depends on your requirements on accuracy. A lot of stuff can be sufficiently approximated with SPICE or a formula based calculator like Saturn PCB.

Usually you know it when you actually need a 3D field solver 

[Damperhead]

Hyperlynx is a traditional SI simulator that can simulate circuit board transmission lines either directly from the board or in shematic freeform format using IBIS models. The simulator is of type 2.5D, i.e. not an actual 3D simulator. The 3D simulator is a reasonable solution for simulating long or otherwise complex hi-speed links or more RF related digital stuff where PCB is involved using S-parameters such as connector pad junctions, differential signal vias etc. This function requires a much more expensive Hyperlynx full solver license. The Basic Hyperlynx SI is moderately priced, versatile and easy to use.

[Pseudobyte]

I would recommend you use a simulation tool to extract your transmission line characteristics for the nets you care about and then put those back into your circuit simulation. The less you try to simulate the better in my experience.

I have done this with PathWave ADS, Ansys SIwave and then thrown the transmission line into PLECS or LTSPICE to see the circuit behavior. ADS is probably the nicest tool to work in for simulation but the price tag is offensive.

[Warhawk]

We normally simulate electronics circuits using SPICE simulators. There are many simulators available for that purpose. One of them is LT SPICE by Analog Devices in which we can add/import 3rd party components in the library and simulate the circuit using their SPICE models.

I am wondering how do we simulate the layout to check the signal and power integrity in the PCB layout. The PCB stackup consist of multiple copper layers for routing signals and power distribution, and there are dielectric materials between the layers. FR4 is an example of dielectric material is widely used in PCB.

The signal quality in the PCB traces depend on the signal switching frequency, rise time, bandwidth and also mainly on the physical design of the layout and dielectric material. Although there are PCB layout design consideration for high speed signals but I am still wondering if there exist a tool which can simulate the transmission lines and is free to use that would be the best. Any suggestion on such simulators ?

To my knowledge, Mentor Graphics does exactly what you need. It can back-annotate the circuit diagram based on the PCB layout and simulate parasitics. They explained it quite in detail to me during PCIM2023. I don't expect you get anything for free or affordable.