A New Approach to Background Noise Cancellation in Time Domain for Low-Frequency Emission Testing

This article proposes a new approach to background noise (BN) cancellation for low-frequency electromagnetic compatibility (EMC) emission testing between 30 Hz and 10 kHz. The method proposed in this article is based on the streaming and recording of oscilloscope data in a continuous period without interruption and without losing phase information. In the proposed method, the continuous and consecutive stream of the oscilloscope data contains two adjacent data segments inside. The first data segment consists of the equipment under test (EUT) and BN information together, whereas the second segment contains only the BN because the EUT is switched off in the middle of the continuous data stream. After gathering all the oscilloscope data, the BN that exists in the first segment is precisely estimated by means of the BN information, which exits in the second segment. This estimation is easily attainable as the phase difference is accurately known between any two points in the first and second segments. Afterward, the simple subtraction of the estimated BN data from the actual combined EUT and BN data yields the EUT time-domain data. The proposed method assumes that the spectral content of the BN is stable during the entire streaming process, which may typically last for a range of 10-20 s. Ultimately, the effective performance of the method for the extraction of the EUT signal from the BN is theoretically and experimentally demonstrated with an average deviation of less than 0.6 dB for the low-frequency emission EMC testing.