A 312-GHz CMOS Injection-Locked Radiator With Chip-and-Package Distributed Antenna

This paper presents an injected-locked THz radiator integrating a half-quadrature voltage-controlled oscillator (HQVCO), four injection-locked frequency quadruplers (ILFQs), and a chip-and-package distributed antenna (DA). At the system level, an architecture based on injection locking is employed to allow individual optimization of the output power and the phase noise. At the circuit level, intrinsic-delay compensation and harmonic boosting techniques are proposed to optimize the phase noise of the HQVCO and the output power of the ILFQs, respectively. The proposed DA composed of four exciting elements on silicon chip and a primary radiator in low-temperature co-fired ceramic (LTCC) package features a wide bandwidth of 13% and a gain of 3.8 dBi without using lens at 312 GHz. Implemented in a 65-nm CMOS process, the radiator system occupying a core area of 0.36 mm² achieves output frequency from 311.6 to 315.5 GHz and maximum equivalent isotropically radiated power (EIRP) of 10.5 dBm while consuming 300 mW. The output phase noise measures -109.3 dBc/Hz at 10-MHz offset and the dc-to-THz efficiency is 0.42%.

I. Introduction

As one of the least tapped regions in electromagnetic (EM) spectrum, the terahertz (THz) band from 0.3 to 3 THz is gaining increasing research interest due to the numerous potential applications uniquely enabled by such short wavelengths including imaging, spectroscopy, and high-speed wireless communications [1]–[4]. In reality, a technology vacuum known as “terahertz gap” exists [5], [6], inducing major challenges in implementing radiation sources with sufficient output power to overcome the severe path loss at such high frequencies. Currently, most THz sources rely on photonic devices such as quantum cascade lasers or compound semiconductor devices such as Gunn and resonant tunneling diodes, which are bulky and expensive [7]–[9]. On the other hand, as the cutoff frequency ( of nanometer-scale CMOS devices gradually approaches sub-THz, fully integrated CMOS solutions with compact form factor, high reliability, and low cost are becoming increasingly promising. Recent works have successfully demonstrated sources and radiators from sub-THz to THz in bulk CMOS [7], [10]–[15] and SiGe BiCMOS [16]–[19]. In [10], a 280-GHz radiator based on 16 distributed active radiating elements is reported, achieving output power of 0.19 mW and equivalent isotropically radiated power (EIRP) of 9.4 dBm. In [12], a 288-GHz signal source with 0.38-mW output power is presented. In [13], the novel self-feeding oscillator array obtains 1.12-mW output power and 15.4-dBm EIRP at 260 GHz. Additionally, the radiator array using 16 coupled oscillators in [14] achieves 338-GHz output with RF power of 0.81 mW and EIRP of 17.1 dBm. In these works, high-order harmonic extraction approach is widely employed to overcome limitations and realize radiation frequency far beyond that achievable from fundamental oscillation. By combining signal powers from a number of integrated elements, either on-chip or in free space, the overall EIRP can be increased to a useful level.