An EMI receiver model with consideration of the intermediate frequency filter
The fast Fourier transform (FFT) is usually used to analyze the spectrum of electromagnetic interference (EMI) noise. However, the calculated spectrum of a noise signal by using a general FFT algorithm is different from the measured result obtained by using an EMI receiver. Because the intermediate frequency (IF) filter in the EMI receiver has a band-pass effect when filtering the signal, the measured spectrum amplitude at any frequency point is not simply the original amplitude of the signal at the frequency, whereas, it is a time-domain superposition result of the signal in the pass-band frequency range of the IF filter. This paper focuses on modelling of an EMI receiver and presents an improved FFT algorithm for simulating the EMI receiver with consideration of the IF filter. Window functions are analyzed and suggested for modelling the IF filter. The improved FFT algorithm is validated through comparison of simulated and measured EMI spectrums.