Rise-Time Calibration of 50-GHz Sampling Oscilloscopes: Intercomparison Between PTB and NPL

We present the results of the first intercomparison of the rise-time calibration of a 50-GHz sampling oscilloscope between Physikalisch-Technische Bundesanstalt, Germany, and National Physical Laboratory, U.K. (EUROMET project 641). Rise-times between 6.0 and 6.6 ps were obtained using optoelectronic techniques. Detailed uncertainty budgets are given, which yield typical rise-time uncertainties of 1.2 ps. The absolute values of the degree of equivalence are $\leq$0.3 ps with an expanded uncertainty of 1.0 ps and, thus, validate the experimental techniques.