A novel realtime time-domain EMI measurement system based on field programmable gate arrays

In the past and now measurements are carried out by EMI-Receivers operating in frequency-domain. By a time-domain EMI (TDEMI) measurement system the measurement time can be reduced by several orders of magnitude. In this paper a novel real-time TDEMI measurement system that uses a direct hardware implementation of the Short Time Fast Fourier Transform (STFFT) and the detector modes is described. The hardware implementation on Field Programmable Gate Arrays (FPGAs) allows to process the input signal in realtime. By the continuous processing via the STFFT the IF-Signal for selectable frequency can be provided as requested by CISPR 16-1-1. By simulations on a proposed FPGA it is shown that the measurement time can be reduced by a factor of about 2000 in comparison to conventional EMI Receivers. The dynamic range of a fixed point FFT has been investigated and it has been shown that a 16-Bit fixed point arithmetic is sufficient to fulfill the requirements according to the international EMC standards. EMI Signals have been recorded and processed by a hardware model. The results have been compared with measurements obtained with a conventional EMI Receiver in the frequency range 30 MHz - 1 GHz.