Electro-optic sampling of coplanar to coaxial transitions to enhance the calibration of fast oscilloscopes

Improvements to the NPL time domain measurement facility for the calibration of fast oscilloscope risetime are described. Particular emphasis is placed on characterising a coplanar waveguide to coaxial connector transition between a photoconductive pulse generator and the input of an oscilloscope sampling head. Two methods of measuring the transition are described and it is shown that test electrical pulses of less than 4 ps width can be applied to the oscilloscope.