Hi, I am using ngspice to run the transient simulation on a post-layout netlist. I keep getting this

Time step too small

error messages. I don't know if the reason is that there are some undefined nodes or singular matrix. However the extracted netlist is too complicated to solve these floating points or singular matrix if these are actually what cause the

Time step too small

error. Does anyone know how to avoid this error? Thanks! It seems that the transient initial op condition of each node is successfully calculated and this error happens during the transient.

You need to resolve the singular matrix issue. Usually some input node is not tied to a voltage source or unconneted.

Thanks @Stefan Schippers. Do you have any advice for an efficient way to do that since my netlist is a post-layout netlist so there are thousands of caps in it. Or I need to do it manually.

If the extraction tool works well it does not create singularities. Verify all standard cells power and well/substrate connections, then verify if all top level inputs are driven. I can't say much more without digging into the netlist. ALso carefully read ngspice logs, usually it lists some nodes that are causing problems, in some cases this information could be useful (this is not always the case, unfortunately).

Thank you so much

Just for testing you can also try to remove all filler cells from the netlist.