10.2 An FSK plastic waveguide communication link in 40nm CMOS

Technology scaling has enabled RF-CMOS circuits that operate in the millimeter-wave frequency range (30 to 300GHz) where large bandwidths are available. These bandwidths can be exploited to increase data-rates of wireless communication links. Unfortunately, free-space path loss (FSPL) limits the operating distance of wireless systems at these frequencies. A 5-meter link at 120GHz has an FSPL as high as 88dB. Therefore such wireless links are feasible only with highly directive antennas. This work uses a directive channel instead. At mm-Wave frequencies, the directive channel can be a low-cost plastic fiber or hollow tube, made from PP, PS or Teflon. These directive channels will guide electromagnetic waves with low loss from TX to RX [1-4]. As such, RF communication through a plastic fiber becomes an interesting alternative and complements existing solutions like wireline copper or optical fibers. This paper presents an entire communication link that uses a continuous-phase frequency-shift keying (CPFSK) TX and RX. We report on 120GHz 40nm CMOS TX and RX chips, the connector solution, and the plastic channel. Data-rates up to 12.7Gb/s over 1m, transmission lengths up to 7m at 2.5Gb/s and an energy efficiency of 1.8pJ/b/m for 4m and 7.4Gb/s are achieved for the complete communication link. All these results are for a BER 10^-12. Compared to previous work, measurements also show the link still works for a bending radius of only 25mm, thanks to the selection of a high carrier frequency.