A 220-GHz BiCMOS Wireless Coherent Transmitter Using Free-Running Oscillators and Kramers–Kronig Technique

For the past few decades, extensive work has been done to realize RF integrated communication circuits at THz (100–1000-GHz) frequencies. However, for silicon-based devices, which are the most commercially accessible, our circuits fail to produce meaningful output power beyond a few hundred GHz, and as the frequency and bandwidth increase, the effects of noise and phase noise become more and more prominent. Until recently, communication systems above f_max /2 have been struggling to reach highly complex (16QAM and above) modulation schemes largely due to difficulties inherent to achieving phase coherency and high SNR. The system presented herein uses a Kramers–Kronig transmitter, which suggests the ability to reconstruct the signal’s phase by only measuring amplitude. We showcase an integrated transmitter that achieves phase coherency using fully on-chip free-running oscillators above f_max/2. By pursuing this style of wireless communications, future works may potentially be able to realize phase-encoded fully integrated systems without off-chip sources or exceedingly difficult PLLs. By reaching high-order QAM schemes, transmitter data rates above 200-GHz carrier have the opportunity to rapidly increase with respect to the current state-of-the-art.