Signal Preprocessor for Determining Time of Arrival

A proposed analog/digital circuit would improve the accuracy of determining the time of occurrence of a peak in an analog waveform. In the past, the time of occurrence of the peak was determined by comparing the magnitude of digital data samples. The time or clock pulse associated with the peak magnitude was taken as the time of occurrence of the peak of the waveform. The new technique saves a series of data samples (7) prior to and after the sample with the largest amplitude. The set of data samples is saved and is used with curve-fitting equations to estimate the time of the peak of the waveform. This can be done because of the deterministic character of the waveforms. This technique allows the time of occurrence of the peak of the waveform to be determined with greater resolution than can be obtained by simply sampling the data and looking for the peak. This technique has applications in systems where it is desirable to determine the relative time between waveforms. The Lightning Detection and Ranging (LDAR) system at KSC uses the differences in the time of arrival of lightning waveforms at seven sites, to locate lightning sources. The technique described is being implemented in the improved system to increase accuracy.