Using spectrograms in EMI-analysis - an overview

Spread-spectrum techniques have raised their importance as a common EMI-reduction technique in power supplies. Ability to track and measure such a signal is vital. Analysis and synthesis of an effective spread-spectrum sequence is also important. Pulse-type and apparently random interference are other types of signals which are hard to detect and measure, but still very common in practice. In this paper a spectrogram, a time-dependent spectrum analysis is proposed as a practical tool for EMC-design and measurements. Basic theory and selected examples of spectrogram in EMC-engineering are presented.