On Moore’s Law and Electromagnetic Interference

On Moore’s Law and Electromagnetic Interference

State-of-the-art transistor technologies bring unparalleled power density and efficiency to a myriad of power conversion applications. The relentless charge down the semiconductor process technology roadmap guarantees ever faster switching speed (dV/dT) and an unintended consequence, electromagnetic interference (EMI).

Moore’s Law has been around a long time. Simply stated it predicts that the number of available gates on a fixed silicon area will double every 18 months based on the continual advancement of semiconductor process technology nodes. An adjunct to Moore’s Law, devised by Robert Dennard, and referred to as Dennard’s Scaling, says that as transistors are systematically reduced in size, their speed increases and their power consumption is reduced. Faster switching (dV/dT), produces more noise in the form of EMI. It can be argued therefore that noise scales with Moore’s Law. Until this cycle is broken, when transistors in their current form cannot be made any smaller, the use of EMI Filters in power conversion applications will increase dramatically in the next decade.

Inverters are in a period of rapid growth fueled by demand in alternative energy markets such as PV, Wind, and Electric Vehicles. Inverters and Industrial Drives are also seeing increased use in the replacement cycle of legacy power sources in products such as Air Conditioners, Welding Equipment, Cutting Tools, and Motion Control. The power required to switch the modern day IGBT or MOSFET is nearing zero, making these devices ideal candidates for inverter and industrial drive power topologies. Although the EMI/RFI signature of a standalone transistor device can be quantified in the lab it is not very useful to the system designer. The way these chips and modules are used and where they are placed within the system are far more deterministic of the resultant emissions produced. Shielding and physical isolation of the offending energy sources can reduce or eliminate radiated emissions in most cases. Robust grounding is critical in the control of conducted EMI.  

While good system design practices can mitigate the majority of issues with conducted and radiated emissions, EMI is often discovered and identified late in the design phase. Low voltage digital electronics and analog-to-digital converters are particularly susceptible in these noisy environments. The price of poor design practice can result in bit or logic errors and voltage reference drifts which can produce aberrant or even dangerous conditions. Once identified in the lab, EMI can be brought under control with the use of power line filtering at the AC input and in some cases also at the DC output. Care must be taken to ensure that the filter specified is within leakage current budgets and that the unit does not introduce excessive capacitance to ground in systems that cannot tolerate it. Costs can be contained by engaging with a Filter Manufacturer who has the capability to conduct pre-compliance testing for conducted emissions on customer products and systems. By testing the end system in house, the customer is afforded an optimized, non-over-engineered, filter solution, be that in the form of a standard product offering or one custom tailored specifically for the application.     

Moore’s law is estimated to be valid for at least another ten years, after which new transistor architectures and substrate materials may be introduced with entirely different attributes. Until then, designers of next generation systems based on these ever shrinking silicon transistors would be wise to consider potential EMI issues and solutions early in the design phase.