A coherent 233-243 GHz scalable 1D array in 28nm bulk CMOS using sub-harmonic inter-element leakage

In this paper, we present a novel method to extend a single-element on-chip sub-THz coherent source to a 1D array without the use of lossy power dividers. In our proposed method we use the leaked fundamental signal from the harmonic generating circuit as an input to the next element chain. To demonstrate this concept a 233-243 GHz 1x2 radiating transmitter (Tx) is presented in TSMC 28nm bulk CMOS. A single Tx consists of 75-84 GHz PA (power amplifier) and a driving stage followed by 75-84 GHz to 225-252 GHz tripler. The leaked signal from the first element is amplified and drives a second tripler element. Biasing control is used to phase shift the signal between elements in the fundamental, thus tripling that phase difference at the radiated output. The outputs of each tripler are connected to on-chip ring antennas that excite the silicon die itself. The lens-less radiating Tx array has a directivity of 7.5 dBi with 52% efficiency and 10 GHz bandwidth, a measured peak EIRP of 10dBm, 3 dBm total radiated power, a DC-to-RF efficiency of 0.8% and demonstrated beam steering.