Sequential sampling time domain reflectometer

Time domain reflectometry (TDR) is a well-known technique used to detect and characterize impedance discontinuities in transmission lines. Usually the application of this technique employs the usage of a step generator to drive one end of the transmission line and a high speed oscilloscope to visualize the signal reflected at various impedance discontinuities points. This paper presents the design and implementation of an USB-based time domain reflectometer which integrates the functions of both equipments and is intended to be a low cost solution for time domain reflectometry. The acquisition technique used is sequential sampling based on integrated delay lines, giving a time step of 250 [ps] at a total acquisition time of about 2.6 [us]. Sequential sampling is successfully used for high speed sampling oscilloscopes and can be implemented using commercially available components. Unlike similar implementations of the method, our proposal uses internal delay calibration to eliminate the ghost effect which limits the minimum measurable cable length. Also, by comparison with random sampling TDRs, our approach allows an improved control over the acquisition parameters.