Don’t Leave Your Power Distribution Networks Vulnerable to Rogue Voltage Waves
2020-01-21 | 4 min read
Power anxiety is a common ailment in our always-on digital culture, especially for road warriors who depend on battery-operated devices. Almost everyone who uses a mobile device has experienced low battery power during a critical business call, laptop presentation, or episode of a favorite show. Not having a backup battery or available electrical outlet can give you a sinking feeling.
There is another kind of power anxiety consumers of electronic products do not think about often. It impacts almost every high-speed digital (HSD) product that uses power, whether provided by a battery or a cable plugged into a wall socket. It is the kind of power distribution network (PDN) problem that can be devasting if product development and power integrity engineers do not account for it during the design and verification process. If taken lightly, this problem can cost electronics manufacturers a bundle in retrofits and design re-spins.
I am talking about voltage noise ripple in PDNs and the possibility of rogue voltage waves. Passengers riding in the next generation of autonomous vehicles are counting on power integrity engineers to ensure that they will not become victims of rogue voltage waves (Figure 1).
Figure 1. Autonomous vehicles generate huge amounts of data from HSD subsystems that depend on resonant-free power delivery
PDNs must provide clean power to the load. Electronic devices have maximum voltages and ripple specifications to avoid damage, lost data, and electromagnetic interference / compliance failures. Traditional methods of measuring noise on a power rail often fail to detect worst-case voltage ripple. They consider only the step load excitation published in component data sheets and the corresponding natural response on the power rail.
When the natural response shows a small amount of voltage ripple, engineers might overlook the forced response of a resonance that can be much larger. Normal operation of the load may never excite this resonant frequency. But digital systems are wideband and difficult to test for all combinations of operating scenarios. For example, power-saving modes that turn on and off and data bursts can create HSD load transients that extend from kilohertz to gigahertz.
The problem is that individual data sheets for electronic components do not include enough information about the end-user application to provide worst-case forced response data. The distributed inductance of the printed circuit board, interconnects, and decoupling capacitors creates a complex dynamic behavior. That complexity is not apparent in the oversimplified data sheet step response. Using simulation tools as part of a modern power integrity workflow prevents failures late in the HSD design process. Moving from a traditional data sheet approach to a modern simulation and measurement workflow produces higher-quality HSD designs. This approach provides resonant-free PDNs that avoid rogue voltage waves.
It takes only one rogue wave to kill a PDN in high-speed digital designs. To learn more about avoiding them in your next design, read the white paper “High-Speed Digital Design Success Demands a Modern Workflow.” Power integrity engineers may want more technical information about flat impedance optimization before layout to lower the risk of PDN failures. Read the application note “Optimize Power Distribution Networks for Flat Impedance.”