A Novel Ultra-fast High Resolution Time-domain EMI Measurement System based on Field Programmable Gate Arrays

Full Compliance Measurements of the electromagnetic interference (EMI) of electric and electronic devices in the past and now is performed with EMI Receivers operating in frequency-domain. Time-domain EMI Measurement Systems allow to reduce the measurement time by several orders of magnitude. In this paper we present a ultra-fast high resolution Time-domain EMI Measurement System that uses three analog-to-digital converters to digitize the signal with an improved dynamic range. Each analog-to-digital converter digitizes a part of the amplitude scale. By a field programmable Gate Array the signal of the three analog-to-digital converters is combined to a signal with high resolution. A novel algorithm to process a real valued signal with a complex DFT is presented. This algorithm allows to speed up to measurement by a factor of about 2000 in comparison to an EMI Receiver. In comparison to a conventional FFT algorithm the calculation time as well as the consumption of logic is reduced by a factor of 2. A further algorithm is shown that can calculate the spectrum with a smaller bin-width than a conventional FFT. By this algorithm an EMI measurement at any frequency independent of discretization given by the FFT in frequency-domain can be performed. The EMI signal of a device has been recorded with a novel multiresolution system that consists of several 10-Bit 2.3 GS/s analog-to-digital converters and processed by an implemented fast Fourier transform on Field Programmable Gate Arrays. The emission of a device under test has been investigated at 19600 discrete spectral values and 36 angles within 3 minutes. The results have been compared with results obtained by an EMI Receiver in the frequency range 30 MHz - 1 GHz.