Quantitative electro-optic sampling for high-speed characterisation of passive and active devices

We report our recent progress on the high-speed sampling of passive circuit elements and active electronic devices. Using optical excitation of picosecond photoconductors and electro-optic sampling, bandwidths of 300-400 GHz and a signal to noise ratio /spl square/60 dB are attainable. By exploiting the spatio-temporal symmetries of coplanar waveguide, the pulses resulting from quasi-TEM CPW modes can be isolated from parasitic slot and slab modes. The stimulus and response were separated using a procedure which avoids 'arbitrary' time-windowing of forward and reflected pulses. The role of probe invasiveness in run-to-run repeatability was identified. Using such methods, we expect that quantitative electro-optic sampling at the few % level can be realised. These methods were used to measure S-parameters of 'standard' impedances for vector network analysers and passive circuit elements including airbridges. Approaches to the high frequency measurement of active devices including 0.1 /spl mu/m T-gate PHEMTs is also discussed.