EMC Performance of Field Programmable Gate-Arrays: Effects of I/O Standards and Attributes on the Radiated Emissions Spectrum

This research investigates what impact the I/O standards & attributes of a Field Programmable Gate Array have on the radiated emissions spectrum. FPGAs are used in countless digital applications. The use of a Spartan-6 FPGA gives a good representation of a general device with Xilinx being the market leader in supplying FPGAs for a variety of industries. The logic standard, drive strength and edge rate are examined for their impact on that radiated emissions produced. Digital integrated circuits are a well-known and documented source of Electromagnetic Interference due to the fast transitions of period signals. A practical and theoretical understanding of the behaviour of clock signals in the time and frequency domains has been established. The impact of phenomena such as overshoot and ringing from practical signals has been considered for its impact on the emissions spectrum and how this deviates from the theoretical expectations. Logic standard, drive strength and edge rate have been assessed comparatively to determine their influence of peak emissions produced. Of the logic standards tested the LVTTL standard recorded the highest level of EMI across all I/O logic standards approximately 4dB higher than the equivalent CMOS standards. The LVTTL standard recorded the largest variation in emissions across the available I/O driver settings with approximately a 14dB increase from the minimum to maximum I/O driver settings. The LVCMOS logic standards recorded on average across the 3.3 volts, 2.5 volts, 1.8 volts, 1.5 volts and 1.2 volts logic, a maximum change to EMI of approximately 10dB from the minimum to maximum driver settings. Each category of the variable I/O driver settings has been assessed independently to assess the level of change to emissions produced. Average levels of EMI produced under each I/O driver setting have also been obtained and presented to give engineers and designers an indication of how decisions made within the design process can influence the level of emissions produced. It is hoped that this research will provide as a useful tool when designing with programmable integrated circuits such as the Spartan-6 FPGA and the potential EMC impact on the radiated emissions spectrum.