The growing demand for high-speed, low-cost, and low-overhead I/Os in today's electronic systems, has been addressed by three general categories of interconnects: electrical, optical, and wireless. The electrical interconnects are the oldest and have improved the most, where bit rates in excess of 20Gb/s are achieved over a pair of conductors [1]. At such high bit rates, these serial links must handle transmission line loss, dispersion, impedance mismatches, and electromagnetic crosstalk among multiple lines requiring sophisticated designs, often needing equalization, with their own cost and overhead limitations [2]. Optical fibers as interconnects do not suffer from similar bandwidth limitations or cross-talk issues. However, they require additional electrical-to-optical (EO) and optical-toelectrical (OE) conversion devices for generation and detection of optical signals [3], which impose serious constraints on power consumption, cost, and footprint of optical interconnects. Wireless connection at millimeter-wave frequencies can also be used for short distance connections [4]. While they provide the most versatility and are a promising option, additional development is still necessary to scale them to a highly parallel system with multiple channels running concurrently.This paper presents a 12.5+12.5Gb/s full-duplex plastic waveguide interconnect solution based on millimeter-wave signal transmission. The plastic waveguide is simply a long solid piece of plastic that provides a very simple, versatile, flexible, and low-cost transmission medium that has the main advantages of optical fiber in isolation and bandwidth, without the need for costly EO and OE. The dielectric waveguide does not need to be connected electrically like the wire or aligned to micron-level accuracy like optical fibers. It can be bent and twisted without significant impact on the signal. Compared to the wireless link discussed earlier, it offers additional signal isolation and confinement. Thus, it can be extended over much longer distances due to the low attenuation in the waveguide (as opposed to free space) and multiple independent lines can be run in parallel to increase the bandwidth.In our proposed plastic waveguide link, the TXs and RXs are fully integrated in CMOS, and the waveguide couplers can be fabricated in a conventional resin package without additional cost. In our existing setting there are a transmitter and a receiver operating at different carrier frequencies on each side of the waveguide, making it possible to realize a full-duplex solution. Because of the smaller fractional bandwidth for the millimeter-wave transmission, no equalization circuit is required. Figure 8.5.1 presents a diagram of our proposed solution. It consists of a pair of transceivers A and B, and a plastic waveguide. Transceiver A contains a 57GHz RX and an 80GHz TX, and Transceiver B contains an 80GHz RX and a 57GHz TX. This combination allows for a bi-directional full-duplex transmission. An alternative is to place both TX on one side and both RX on the...
