Frequency based oscilloscope triggering scheme

Abstract

This paper presents a novel frequency based oscilloscope triggering technique for measurements involving complex waveforms that are challenging even today. Proposed technique is capable of providing stable triggering even in the case of complex periodic waveforms category where commonly used level triggering scheme fail to perform adequately and may be used in problem of estimating many typical signal processing situations, such as Doppler estimation of radar and sonar returns, vibration measurements, geophysical data processing, and surveillance observations of the electromagnetic spectrum. For stable display of a signal in an oscilloscope, it must be triggered at its base frequency. In this technique, frequency of all harmonics present in test signal is retrieved using FFT and the base repetition rate of the signal is found by selecting the frequency of lowest harmonics present in the test signal. Numerous complex test waveforms are generated and their harmonic contents are analyzed in the virtual environment of LabVIEW™ software. To verify the efficacy of the proposed technique, it is implemented using LabVIEW™ software and PCI DAQ card. It is found that the proposed technique is equally effective in detecting the base repetition rate of complex as well as simple waveforms. Technique proposed in this paper would be of interest to instrumentation design engineers.