Coplanar-waveguide test fixture for characterisation of high-speed digital circuits up to 40 Gbit/s

For the characterisation of high-speed digital ICs, the standard test fixtures or test boards are usually realised with the microstripline configuration. The input and output impedance of the signal ports are well matched to 50 Omega . Because of dispersion, mutual coupling and reflections at taper sections, which are necessary to produce a change in linewidth in the region where the device is bonded into the test circuit, the performance is limited to the lower gigahertz region. To overcome most of these problems many investigations are being carried out using coplanar-waveguide (CPW) structures. The authors demonstrate the advantage of CPW lines and describe a successful design of a CPW test fixture with low dispersion, a minimum of crosstalk and low reflections suitable for data rates up to 40 Gbit/s.