Sub-harmonic wireless injection locking of a THz CMOS chip array

A novel concept is introduced for generating high power frequency locked THz radiating based on CMOS chips. The concept is based on an array of CMOS VCO chips with on-chip ring antennas. With fundamental mm-wave oscillation around 115 GHz, the 3rd harmonic of 0.35 THz is radiated with record total radiated power (TRP) of -4.3 dBm, EIRP of +3.8 dBm, DC-to-THz efficiency of 1.4% and phase noise better than -95 dBc/Hz at 10 MHz offset. Using a buffer-less Colpitts topology both improves the output power and efficiency but also allows wireless locking of the VCO fundamental frequency using the on-chip antenna, which is an RF-choke for that frequency. This allows wireless coupling between array CMOS chip elements integrated on-board for mutual locking and also wireless locking to an external D-band reference. The concept is demonstrated using a 1×4 array of CMOS radiating chips. The sources can be tuned from 343 to 347 GHz and the injection locking range is around 80 MHz. The 1×4 array has an EIRP of +13.8 dBm, a TRP and DC-to-THz efficiency of +1 dBm and 1.2%, respectively. The 1×4 array locked signal follows the phase noise of the external reference (+9.5 dB) up to a locking range around 80 MHz. This new concept enables simple and cost effective locked CMOS THz scalable source arrays.