Huy Thong Nguyen

A computational approach to automate mm-wave Directional Couplers can greatly improve upon the current techniques that rely on trial-and-error. To build such an automated framework, we propose a Machine Learning technique that, within a computational time of seconds, can fully automate the physical realizations of mm-wave Directional Couplers over a wide range of electrical specifications and metal options. Our proposed technique includes the training of fully connected neural networks that accurately learn the physical-electrical relationships of coupled lines and includes the multi-head gradient-based optimizers that optimally compute the physical dimensions for given design specifications. By demonstrating the automated designs of mm-wave Directional Couplers with numerous coupling factors and dielectric thicknesses, we verify the effectiveness of our proposed computational method.

Mm-Wave 5G links and many emerging mission-critical DoD applications have recently stimulated major research efforts on next-generation mm-Wave power amplifiers (PAs) to deliver nearly "perfect" large-signal performance. Compared to compound semiconductors, silicon often exhibits inferior device-level capabilities on power density, gain, efficiency, linearity, and reliability. On the other hand, silicon technologies offer matured modeling, flexible back-end options, and extensive digital controls, making them a highly versatile and attractive platform for design innovations and system integrations. This paper reviews several recent silicon mm-Wave PAs from multiple research groups, which all leverage architecture/circuit innovations to overcome device limitations and radically advance the state of the art. These design explorations include Doherty/Outphasing active load modulation, continuous-mode operation, broadband harmonic tuning, nonlinearity cancellation, and power-DACs.

We propose a Doherty power amplifier architecture with impedance inverting balun and impedance scaling balun to support Doherty active load modulation and Power Back-Off (PBO) efficiency enhancement at high mm-Wave frequencies. Unlike transformer baluns often used at RF frequencies, mm-Wave coupler-based baluns are employed to provide well balanced differential-to-single-ended conversion and absorb device output parasitic capacitance. Moreover, this paper reports that coupler-based balun with 45° electrical length exhibits impedance inverting behavior, which is utilized to construct Doherty active load modulation network in the reported PA design. Adaptive biasing circuit further enhances the Main/Auxiliary PA cooperation. The measured Doherty PA exhibits 20.1dBm P sat , 19.3dBm P 1dB , and 26% peak PAE. At 7dB PBO, the measured PAE is 16.6%, demonstrating 1.45× efficiency enhancement compared to an ideal class-B PA with the same peak PAE at P 1dB .

This paper presents a packaged 28-GHz Chireix outphasing transmitter (TX) for power amplifier (PA) efficiency enhancement at both peak and back-off output power (PBO). The main objective is to investigate the possibility of employing a multi-feed antenna as a multi-port passive network to perform outphasing active load modulation. As a proof of concept, an outphasing TX architecture is proposed by leveraging a dual-feed loop antenna (DLA) to achieve high efficiency transmission of wideband complex modulated signals. Theoretical analysis and simulation results prove that the proposed DLA is electrically equivalent to an ideal differential series non-isolating power combiner, enabling superior on-antenna outphasing operation. Multi-functional signal processing is therefore achieved in a single loop-antenna footprint, including high-efficiency on-antenna power combining, outphasing active load modulation, and millimeter-wave (mm-Wave) signal radiation. Moreover, unlike conventional spatial vectorial combining techniques (e.g., spatial IQ or spatial outphasing), the antenna-level signal processing preserves the wide antenna unit field of view (FoV) and is particularly suitable for array or multiple-input-multiple-output (MIMO) applications. The proposed Chireix TX contains two phase-shifted sub-TXs simultaneously driving a DLA on package. The measurements demonstrate a 53%/43% PA drain/poweradded efficiency (DE/PAE) at 17.1-dBm saturated output power (P _sat ) and 36%/23% DE/PAE at 6-dB PBO. The high-efficiency Chireix TX supports up to 15 Gb/s 64-QAM with 10.4-dBm average output power and 34% average PA DE (19.2% average PAE) while maintaining EVM/ACLR better than -27.5 dBc/-28 dBc in a wireless radiation testing environment.

A novel W-band (75-110 GHz) surface micromachined Vivaldi antenna fed with a new combination of coplanar waveguide and substrate-integrated waveguide is proposed. The design procedure of the feeding structure and the effects of the antenna's key structural features on its return loss and gain are studied in detail. The selected exponential taper with optimized feeding parameters results in a significantly higher gain (gain > 10 dBi) compared to similar tapered slot antennas reported in the literature over the entire bandwidth of operation. The antenna is fabricated using microfabrication processes, and high correlations between simulation and measurement results confirm its low-loss performance and symmetric and stable radiation pattern over the entire frequency range of 75-110 GHz.

This paper reports the performance of multiple V-band on-chip antennas implemented in Globalfoundries 45nm CMOS SOI process with high-resistivity substrate option. Dipole, slot and loop antennas are implemented as proof-of-concept designs. The antenna samples are flip-chip packaged on a PCB for testing. After de-embedding the loss from the feeding/matching network, the measured boresight antenna gains of the dipole, slot and loop are 3.9dBi, 3.8dBi and 3.7dBi, respectively, matching well with the 3D EM simulations. The measured radiation efficiencies are greater than 79% for all the three cases. Compared to other on-chip/on-package mm-Wave antennas, the demonstrated antennas are fully integrated in CMOS SOI process and do not require any post-processing, substrate-thinning/etching, lossy chip-to-package interconnections, or silicon lenses. It is demonstrated that the high-resistivity substrate option in Globalfoundries 45nm CMOS SOI technology is an effective solution to support high-efficiency and high-performance mm-Wave on-chip antennas, which paves the way for highly integrated mm-Wave transceiver systems including 5G phased arrays and massive MIMO systems.