29.9 A 4×4 Distributed Multi-Layer Oscillator Network for Harmonic Injection and THz Beamforming with 14dBm EIRP at 416GHz in a Lensless 65nm CMOS IC
Hooman Saeidi, Suresh Venkatesh, Chandrakanth Reddy Chappidi, Tushar Sharma, Chengjie Zhu, Kaushik Sengupta
Abstract
Integrated high-power THz arrays with beamforming ability can enable new applications in communication, sensing, imaging, and spectroscopy [1]. However, due to the limited power-generation capability of a single source above the device f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> [2], efficient spatial power combining from multiple coherent sources becomes necessary to generate mW level of power. To create this 2D array of distributed frequency and phase-locked sources, prior works have shown central LO-signal distribution with local harmonic upconversion [3]. However, this requires high power consumption in the LO distribution. In addition, phase-matching with PVT variations across the sources at the harmonic-radiating THz frequency can be quite challenging. A small Δθ perturbation at the fundamental frequency translates to NΔθ at the radiated N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic, thus corrupting the array beam pattern. Another method to synchronize multiple distributed radiating sources (λ/2 spaced at Nfo) is through a mutual coupling network with active/passive elements in a coupled oscillator array [4], [5]. However, the locking range in these methods is typically narrow (Δf <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">locking</sub> ~ f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /20 to f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /10) and PVT variations can easily cause desynchronization. In such a network, each cell is a self-sustaining oscillator, and the coupling network tries to establish injection signals to force synchronization between these individual free-running oscillators. In this paper, we used a 2D oscillating network with negative G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> (-G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ) cells at each node that do not oscillate individually but only collectively, establishing a robust frequency and phase distribution network across the chip for high THz-power generation. By making this network as the lowest layer, we can now separate the locking mechanism and the power-generation sources. This avoids loading and sub-optimal operation of the power sources. The distributed oscillating network at the lowest layer operates at 69.3GHz, and multi-layer local harmonic generation produces a radiated power of -3dBm and +14dBm EIRP at 416GHz in a 4×4 array.