![]() There are many other free calculators but be careful to check the validity of their underlying calculations as the formulas used by some are only applicable for certain trace width to separation ratios). Trace spacings and width can then be calculated pretty accurately using free tools like MWI2020 (()) and MLDTLC (Multi-Layer Dielectric Transmission Line Calculator field solver tool: ()). Note: if a PCB manufacturer does not publish information about their board stackups and materials then it is very unlikely that they are going to be a suitable supplier of controlled impedance boards. Once the transmission line structure has been chosen, the spacings between the relevant copper layers and the dielectric constant(s) of the substrate layer(s) between them can be found by querying the PCB manufacturer's information about board stackups and materials. Trace spacings to ground planes and other transmission line elements Spacings between the relevant copper layers ĭielectric constant(s) of the substrate layer(s) between the relevant copper layers Transmission line structure (surface/covered/buried/differential/coplanar microstrip, simple/offset/edge-coupled/broadside-coupled stripline) The basic physical parameters required to design controlled impedance PCB tracks are: **How to design controlled impedance tracks** Thee is a very simple example of a transmission line with discontinuities here: Any discontinuities caused by varations in trace width and transitions through vias and connectors can often be modelled simply by inserting short propagation delay lengths of different impednces or by breaking the line up into shorter delay time segments and connecting small capacitances to ground and small inductances in series to simulate the discontinuities. In most simulations it is the detailed characteristics of the signal source and the line termination that will have the greatest effect on the signal integrity. In fact the G component is often not implemented in the spice RLGC models as it can usually be ignored. A lossy, RLGC model can be used if the characteritics of the line can be calculated or measured in more detail but this is usually only required in special circumstances such as very long lines or operation at the upper end of a material's frequency range. **How to model controlled impedance tracks**įor most simulations of controlled impedance tracks a lossless transmission line model is all that is required to simulate the trace. However, since this type of modelling tends to piecemeal in that it is not usually carried out on the whole of a schematic that is to be converted into a PCB there is actually no reason why this simulation work could not be better carried out on a local installation of LTspiceXVII or Qucs-S following the same procedure as outlined below. I have posted a Bug Report about his here: Please note that in the course of writing the notes below, I have discovered that the Tline model in EasyEDA is broken. QUCS may be a more suitable tool because it has some dedicated substrate and physical transmission line modelling features but it has no interfaces to create properly documented schematics including BoM and PCB Footprint information nor any way to interface to a PCB layout no specific document in EasyEDA describing how to model PCB tracks. There may be better tools for this such as the high end tools from Keysight, Mentor and Cadence but of course they are expensive. Running the simulation from there is easy. ![]() There are also a couple of ADC and DAC device models.Ĭoming back to your question however, simulations of PCBs traces and device interfaces can be done in EasyEDA but you have to appreciate that it is a labour intensive task because you have to find the PCB dielectric and copper parameters to calculate the trace impedance and lengths and then manually implement those parameters in individual transmission line segments to map the PCB back into a representative schematic. ![]() That said there are spice symbol libraries in EasyEDA with detailed behavioural models of 74HC and 4000 series devices many of which are in fact modelled as state machines. ![]() Such devices require far too much processor time to simulate using spice simulation tools even when using the built-in digital modelling features of simulators like LTspice or Ngspice. Simulation of digital circuits is very much possible using EasyEDA but it is not the best tool for trying to model clocked devices with complex internal states programmable devices such as microcontroller. I think you misread the Preliminary Remarks in the Simulation Tutorial. "It is stated in the simulation intro that it is not possible to simulate digital circuits in EasyEDA." ![]()
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