25.5 A 320GHz phase-locked transmitter with 3.3mW radiated power and 22.5dBm EIRP for heterodyne THz imaging systems

Non-ionizing terahertz imaging using solid-state integrated electronics has been gaining increasing attention over the past few years. However, there are currently several factors that deter the implementations of fully-integrated imaging systems. Due to the lack of low-noise amplification above fmax, the sensitivity of THz pixels on silicon cannot match that of its mm-Wave or light-wave counterparts. This, combined with the focal-plane array configuration adopted by previous sensors, requires exceedingly large power for the illumination sources. Previous works on silicon have demonstrated 1mW radiation [1,3]; but higher power, as well as energy efficiency, are needed for a practical imaging system. In addition, heterodyne imaging scheme was demonstrated to be very effective in enhancing detection sensitivity [4]. Due to the preservation of phase information, it also enables digital beam forming with a small number of receiver units. This however requires phase locking between the THz source and receiver LO with a small frequency offset (IF<;1GHz). In [5], a 300GHz PLL is reported with probed output. In this paper, a 320GHz transmitter using SiGe HBTs is presented (Fig. 25.5.1). Combining 16 coherent radiators, this work achieves 3.3mW radiated power with 0.54% DC-RF efficiency, which are the highest among state-of-the-art silicon THz radiators shown in the comparison table in Fig. 25.5.6. Meanwhile, the output beam is phase-locked by a fully-integrated PLL, which enables high-performance heterodyne imaging systems.