Defect Identification in Branched Traces by High-resolution Time-domain Reflectometry

A quick identification of the defect over a single trace is usually done by a time-domain reflectometry (TDR). However, TDR waveforms might not be comprehended had the defect been hidden in a trace with multiple branches, owing to many reflection points. A high-resolution TDR utilizing electro-optical sampling has not only a superior resolution in the femtosecond level, but also more comprehensible impulse waveform, leading to the opportunity of identifying defect from a complex waveform. TDR waveforms consists of defect dependent reflection (DDR) and defect independent reflection (DIR). Generally, the signal reflected from the trace with a defect, or DDR, is quite simple: a positive pulse is reflected from open (high impedance); a negative pulse is reflected from short (low impedance). The signal reflected from remaining branched traces, or DIR, are more complex, adding disturbance to the DDR and resulting into a hard-to-understand TDR waveform. In this work, the open-short normalization method (OSN) is applied in the high-resolution TDR measurements to identify the defect’s location and the defect’s type of a BUS network with 4 devices.