Guest Editors' Introduction: Design and Testing of Millimeter-Wave/Subterahertz Circuits and Systems

h IT IS OUR pleasure to introduce this Special Issue on the Design and Testing of Millimeter-Wave/ Subterahertz Circuits and Systems. Recent advances in silicon technologies have opened up new opportunities for investigations into millimeter-wave (mmwave) and subterahertz (sub-THz) circuits and systems. Mm-wave and sub-THz circuits have enabled extremely high-data-rate communications. Hence, many applications like high-definition media transfer, wireless network-on-chip (NoC), and highfrequency radar, have evolved to incorporate these technologies. Work on wireless NoC is more focused on high-data-rate low-power communications within a few centimeters of distance, while multimedia and radar applications require longer distance communication. Hence, the transceiver topologies adopted in these cases are quite different with varying foci. The design and testing of mm-wave and sub-THz circuits face several challenges. In the design phase, accurate modeling of active devices, passive components, as well as interconnects, is difficult and yet crucial at such high frequencies, and often requires time-consuming iterations. As for measurement and testing, proper methodologies of test setup and deembedding at mm-wave and sub-THz frequencies are pivotal. Moreover, for high-volume production, solutions for online tests of these high-frequency circuits are still nonstandard. Hence, high-speed signal processing and coding techniques need to be developed for small penalty of area and power. In addition, consideration of built-in self-testing and self-healing techniques is becoming crucial to the mm-wave and sub-THz circuits due to their sensitivity to process, voltage, and temperature variations. This special issue creates a focused forum on emerging solutions in design and testing of mmwave and sub-THz circuits and systems. The selected papers cover a wide range of topics, from adaptive self-healing mm-wave circuits, to the use of mm-wave wireless channels in intrachip communications and acceleration of 3-D IC testing, and investigations in mixer design and test methodologies. In ‘‘Adaptive Circuit Design Methodology and Test Applied to Millimeter-Wave Circuits,’’ Plouchart et al. present a theoretical framework on the prediction of mm-wave circuit performance by indirect sensing with Bayesian fusion. The authors also present a design example of a 60-GHz LNAwith self-healing function using the proposed indirect sensing method.