Signal integrity-Finding IC signal integrity problems-pcb

- Feb 07, 2017-

Signal integrity-Finding IC signal integrity

problems-pcb

Finding IC signal integrity problems

Typically, an IC designer would take the following steps for SI verification:

  • Perform a layout extraction to get the parasitics associated with the layout. Usually worst-case parasitics and best-case parasitics are extracted and used in the simulations. For ICs, unlike PCBs, physical measurement of the parasitics is almost never done, since in-situ measurements with external equipment are extremely difficult. Furthermore, any measurement would occur after the chip has been created, which is too late to fix any problems observed.

  • Create a list of expected noise events, including different types of noise, such as coupling and charge sharing.

  • Create a model for each noise event. It is critical that the model be as accurate as possible.

  • For each signal event, decide how to excite the circuit so that the noise event will occur.

  • Create a SPICE (or another circuit simulator) netlist that represents the desired excitation, to include as many effects (such as parasitic inductance and capacitance, and various distortion effects) as possible.

  • Run SPICE simulations. Analyze the simulation results and decide whether any re-design is required. It is common to analyze the results with an eye pattern and by calculating a timing budget.

Modern signal integrity tools for IC design perform all these steps automatically, producing reports that give a design a clean bill of health, or a list of problems that must be fixed. However, such tools generally are not applied across an entire IC, but only selected signals of interest.


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