324GHz CMOS VCO Using Linear Superimposition Technique

Terahertz (frequencies ranged from 300GHz to 3THz) imaging and spectroscopic systems have drawn increasing attention recently due to their unique capabilities in detecting and possibly analyzing concealed objects. The generation of terahertz signals is nonetheless nontrivial and traditionally accomplished by using either free-electron radiation, optical lasers, Gunn diodes or fundamental oscillation by using III-V based HBT/HEMT technology[1-3]. These prior techniques suffered major disadvantages of size, cost, complexity and sometimes even the need of cryogenic cooling[2]. CMOS has never been considered for terahertz applications due to its low cut-off frequency of fmax. The highest reported CMOS oscillation frequency to date is 192GHz through a 2nd order push-push method[4]. We have substantially extended the operation range of deep-scaled CMOS by using a linear superimposition method, in which we have realized a 324GHz VCO in 90nm digital CMOS with 4GHz tuning range under 1V supply voltage. This may also pave the way for ultra-high data rate wireless communications beyond that of IEEE 802.15.3c and reach data rates comparable to that of fiber optical communications, such as OC768 (40Gbps) and beyond. Our new approach does not rely on device nonlinearities, but employs linear superimposition of multiple phase-shifted (2π/N in sequence, where N is an integer greater than one) and rectifie