Get email delivery of the Cadence blog featured here
One way to determine if your design can withstand an electro-static discharge (ESD) event is to test it in the lab with an ESD gun. It might work. But it might not. If it does not, it is going to be a time consuming and expensive process to find a way to improve the design. And even if it does work, can you be sure that you did not add more transient voltage suppression (TVS) diodes than were required. Your competitor may have a less expensive design that performs just as well as your design. So, yes, lab testing is one method, but it is not ideal.
A better way is to simulate the ESD event before the design is built. If it passes, you can look at optimizing the cost. If it fails, you can make adjustment to the design without having to build a new PCB. Simulation saves time and money.
Okay, so it is decided. Let’s simulate. But is there really a tool that can simulate an ESD event and the impact it will have on the design? If you do a little searching, you might not find much. A trustworthy ESD simulation requires some rather advanced field solvers and circuit simulators. Some tool providers have opted to provided guidelines for ESD protection, but it is pretty rare to find a tool that can reliably predict ESD impact on a system before the actual hardware is manufactured and tested.
Figure 1 Sigrity SPEED2000™ technology provide reliable ESD simulation
Video: Watch Sigrity SPEED2000™ technology provide reliable ESD simulation
So, what exactly is ESD? What happens with an ESD event is a sudden flow of electricity through objects with electrical charges? This can happen when a person with electrical charges touches a cellphone, or a cable with charges plugs into a USB port.
The discharge can result in voltage measured in thousands of volts with several amperes of current. That is serious and can damage or destroy an electronic device or an electrical system. A high speed digital system that suffers an ESD event may behave strangely for a period of time, for example, your cell phone may drop calls or a laptop computer might start operating with errors.
So, the problem is serious and simulating sounds like a good idea. If you are not simulating ESD today, how will you choose a simulation tool? What requirements does a tool have to meet in order to simulate ESD impact so that designers will know how a design will behave under ESD stimulus in lab?
Because ESD is a transient phenomenon with very high voltage and can cause a large amount of unwanted current through any part of a system, the simulation tool needs to have a time domain simulator with a field solver to model any conductor shapes/traces; it also needs to handle non-linear devices to analyze signals and optimize ESD protection, such as TVS diodes. With all these conditions satisfied, an ESD simulation function actually serves as a virtual lab that can perform standard ESD tests and show you simulation results you can trust.
Sigrity SPEED2000 technology stands up to the ESD simulation challenge and provides a practical workflow for the virtual environment. The goal is to help designers to achieve a high-speed system design that will not fail ESD tests without over-designing ESD protection.
The ESD workflow utilizes the unique hybrid time domain solver to simulate the ESD gun circuit and actual system configuration. Utilizing a pre-configured ESD gun model that satisfies the lab test standard in IEC 61000-4-2, engineers can simulate the ESD event. Placing the gun model at any spot on a PCB/package layout simply mimics what happens in the lab when a real ESD gun zaps a real PCB. The gun model generates the standard specified voltage and current to the system; with all the conductor parts properly modeled, the tool captures ESD current going through the paths that current would travel in a real test environment, and measures the high voltages at component pins. Such information tells engineers if the IC components on board are able to withstand the ESD impact. Engineers can determine whether more protection is needed, or excessive protection should be removed to reduce the cost.
One tip for designers is to not rely solely on TVS devices for ESD protection on your PCB. Other PCB components, such as decoupling capacitors or damping resistors, can provide a certain level of protection as well. Using the SPEED2000 workflow, one can easily examine the contribution of these components to ESD protection, therefore, reduce the use of TVS devices.
We welcome your comments below on simulating your PCB to ensure it meets ESD testing requirements.