Extended Data Fig. 2: Structure of the distributed linear waveguide.
From: An integrated microwave neural network for broadband computation and communication
a, Top view of the each tunable linear waveguide (B, C and D) that produces linear modes. Switches S1,2….6 are inserted periodically along the length of the transmission line and make it tunable in length, with subsegments TLine1,2…6. Shorting the line through these switches alters the effective length of the waveguide to support different fundamental frequencies. b, Cross-section of RF-optimized and digital metal layers in the 45 nm Silicon-on-Insulator CMOS metal stack. Here, the top three layers are via’ed together for low-loss transmission. The five metal layers below are used for routing control signals from a Serial-to-Parallel Interface, to the switches, and also via’ed together to form a low-loss return path to the power supply. c, A schematic of the linear waveguide resonators, with options to lengthen or shorten the return path of the microwave signal. In the experiments, however, for simplicity, only the shortest path (configuration with all switches turned on) was used for training in the machine learning tasks.
