An Introduction To FFT EMI Receivers

An evolution in EMI receiver design is underway to take advantage of today’s digital signal processing (DSP) technologies, using fast Fourier transform (FFT) techniques to simultaneously measure emissions over a wide frequency range, of greater 100 MHz, with greater dynamic range then traditional receivers. Advantages are numerous, allowing new and creative ways to streamline EMC testing. This drive for greater efficiencies is spurred by the desire to increase competitive advantages through reducing product test effort, thereby improving time to market. Due to the versatility of the EMI receiver in the areas of site qualification, pre-test, mitigation, and formal test, efficiency gains related to the EMI receiver have potentially the greatest impact on EMC test processes. These benefits are achieved by measuring emissions over a frequency range in only a few seconds, versus hours compared with more traditional methods using older receiver technologies. To take advantage of the full benefit of this technology, a complete redesign is required, rather than bolting FFT DSP circuitry into existing architectures. This paper provides basic information about FFT and the benefits of the DSP-based EMI receiver using FFT measurement methods.