Challenges of Time Domain Near Field Measurement of Complex Digital Circuit

A time domain near field scanning process is applied to a simple digital PCB to characterize its electromagnetic emission properties. A two probe near field scanning system is employed to obtain the digital circuit emission signal and also the reference signal from a power supply cable. The presence of electric jitter on the measured waveforms has made the processing and synchronization of the measured data problematic. It is infeasible to apply waveform averaging directly on the oscilloscope in order to reduce the measurement noise therefore correlation functions of reference signals are calculated to obtain the delay between each pulse and then align them properly. This process does not address the problem of jitter within the waveform.