Utilizing Frequency Folding in Multichannel Measurements for Broadband EMI Measurements

Due to the global electrification efforts, the electromagnetic environment has become increasingly complex. Therefore new, more advanced electromagnetic interference measurement methods are being developed, where multichannel measurement techniques have gained attention in recent years. This paper describes the utilization of frequency folding in oscilloscopes that do not have an anti-aliasing filter. To exploit this mixing effect, a filter structure is proposed where each filter has a bandwidth which is a multiple of the Nyquist frequency, extending the frequency range of the low-end oscilloscope. The filter structure was tested using a multi-tone test signal. It was possible to reconstruct the frequency components outside the original bandwidth and therefore effectively, tripling the measurement frequency range by simultaneously measuring the first three Nyquist zones.