Gigabit electronics—A review

Digital electronics at gigabit-per-second data rates is emerging as a new branch of science and engineering. A particular field of application opens up in advanced radar and sensing systems where large amounts of data have to be dealt with in real time. Analog-to-digital (A/D) converters with microwave sampling rates and multipliers for high-data-yield processing are specifically required subcircuits. In communications, special 1 to 2 Gbit/s systems have been developed, but a further commercial need develops in domestic satellite links and in fiber-optical communications with its potential high bandwidth capabilities. Corresponding gigabit measuring and test instrumentation is required and being implemented. Gigabit circuitry has so far mainly been realized in hybrid-integrated technology. However, the full use of modern technological tools now allows for the fabrication of gigabit monolithic integrated circuits (IC´s), with circuits up to 4 Gbit/s implemented. In circuit design, specific problems must be solved which are due to the involved wide bandwidths at microwave spectral frequencies. High packing density is required for low interconnection delay, but power dissipation leads to limitations. Gigabit electronics is based on devices with switching speeds in the range of a few hundred picoseconds and lower. Besides pin diodes and Schottky diodes, transistors are investigated at first. While the Si bi-polar has been improved, it is the GaAs MESFET and the GaAs junction FET which excel in speed, with LSI capabilities. Very recently, a considerable speed improvement was reported for Si n-MOSFET´s. Unique properties for gigabit logic are shown by transferred-electron devices. However, the lead with regard to high speed and low power have Josephson junctions of the in-line junction and of the interferometer types. The present phase of rapid gigabit IC development, with expected LSI circuits in the 2 to 5 Gbit/s range and MSI circuits up to 15 Gbit/s, will stimulate further applications.