Pilsoon Choi

A case for leveraging 802.11p for direct phone-to-phone communications

WiFi cannot effectively handle the demands of device-to-device communication between phones, due to insufficient range and poor reliability. We make the case for using IEEE 802.11p DSRC instead, which has been adopted for vehicle-to-vehicle communications, providing lower latency and longer range. We demonstrate a prototype motivated by a novel fabrication process that deposits both III-V and CMOS devices on the same die. In our system prototype, the designed RF front-end is interfaced with a baseband processor on an FPGA, connected to Android phones. It consumes 0.02uJ/bit across 100m assuming free space. Application-level power control dramatically reduces power consumption by 47-56%.

A 5.9-GHz Fully Integrated GaN Frontend Design With Physics-Based RF Compact Model

This paper presents the design of a fully integrated high-efficiency and high-power RF frontend for the IEEE 802.11p standard in GaN HEMT technology. An embedded transmitter/receiver (Tx/Rx) switching scheme and a dual-bias power amplifier linearization technique are used to improve Tx efficiency and linearity. An accurate physics-based nonlinear large-signal device model is developed and used for the design, providing insight into the impact of the behavioral nuances of the GaN HEMTs on RF circuit performance. The fully integrated RF frontend is fabricated in 0.25- μm GaN-on-SiC technology and occupies only 2 mm × 1.2 mm. The Tx branch achieves 48.5% drain efficiency at 33.9 dBm, Psat with 28-V supply. With orthogonal frequency-division multiplexing modulated signals, it achieves 30% average efficiency at 27.8-dBm output power while meeting the -25-dB error vector magnitude limit without predistortion. The Rx branch achieves +22-dBm output third-order intercept point with 3.7-dB noise figure at 12-V supply. The fully integrated high-efficiency and linear RF frontend designed with physics-based RF GaN compact models is demonstrated for the first time for future device-to-device applications.

28.8 dBm, High Efficiency, Linear GaN Power Amplifier With In-Phase Power Combining for IEEE 802.11p Applications

This letter presents a power amplifier (PA) for IEEE802.11p applications, adopting a new power combining technique in a 250 nm GaN process. The proposed technique is used to improve the drain efficiency (DE) across the output power levels and meet the stringent error vector magnitude (EVM) requirement without any complicated input and output networks. The PA is implemented with a fabricated GaN die using the chip-on-board (COB) technology and tested with 27 Mbps IEEE802.11p signal. It achieves -30.5 dB EVM at 28.8 dBm output power with a back-off DE of 22.4% at 30 V supply at 5.72 GHz without pre-distortion. It also maintains more than 22% DE through supply voltage control while meeting its linearity requirement across the wide range of output power levels. The proposed circuit technique is viable for improving efficiency and optimizing linearity with its simple architecture.

High Q VCO using an electro-acoustic device compatible with CMOS integrated circuit technology

Low phase noise characteristic can be in a VCO (Voltage Controlled Oscillator) by using a high Q SAW (Surface Acoustic Wave) device. In this type of VCO, new method for obtaining both wide tuning range and low phase noise characteristic is proposed and experimentally verified. This paper also shows the feasibility of single chip VCOs using PLIC (Poly-Lithic Integrated Circuit) technology compatible with CMOS integrated circuit technology, which allows us to develop a true single chip mobile communication system.

Reference SAW oscillator on quartz-on-silicon (QoS) wafer for polylithic integration of true single chip radio

This paper presents an electro-acoustic circuit fabricated on quartz directly bonded on the processed silicon wafer (QoS), which allows us to polylithically integrate high precision passives with integrated circuits. We first fabricated a prototype SAW resonator and oscillator on thick QoS. The SAW resonator on QoS shows Q about 10,000 and 11 dB insertion loss at 289 MHz, and SAW oscillator on QoS shows phase noise as small as 120 dBc at 10 kHz offset, demonstrating the feasibility of a true single chip radio.

A Fully Integrated Inductor-Based GaN Boost Converter With Self-Generated Switching Signal for Vehicular Applications

An inductor-based GaN dc-boost converter with self-generated switching signal is proposed to remove power and area consuming gate drivers for toggling a large transistor switch. All the active and passive components are integrated on a 3 mm ×3 mm die using 0.25-μm GaN-on-SiC process. The circuit operates at 680-MHz switching frequency with 0.24 W/mm2 power density at 20-V output voltage for vehicular applications with 12-V car battery input.

MIT virtual source GaNFET-RF compact model for GaN HEMTs: From device physics to RF frontend circuit design and validation

A physics-based compact transport and charge model for RF-GaN HEMTs has been developed, including device self-heating, non-linear access region behavior, noise, etc. The model is validated against measurements from device-level DC up to circuit-level. The model is implemented in Verilog-A that is a suitable base for circuit simulations.

GaNFET compact model for linking device physics, high voltage circuit design and technology optimization

This work is the first demonstration of a physics-based GaN HEMT compact model that is calibrated and verified all the way from individual device-to a HV-buck converter circuit, along with an illustration of use in technology optimization. GaN HEMT based high voltage (HV) switching converters are gaining foothold in the medium voltage (<;1000 V) power conversion applications. The superior breakdown voltage, operating frequency, and high temperature performance of GaN HEMTs enable improved conversion efficiency and smaller footprint of the converters [1]. In order to design such high voltage GaN circuits, the device compact model must accurately describe static and dynamic switching behavior to enable designers to gain insight into the impact of the behavioral nuances of the GaN HEMTs on HV circuit performance, such as non-quasi-statics, which is not possible with the available models such as EEHEMT, Curtice, and Angelov models [2]. The model is validated against DC-IV, -CV, and pulsed-IV measurements of fabricated devices and is then verified by comparing measured and simulated signals in a commercial buck converter. Furthermore we demonstrate that our physics-based model can be used as a device design and multi-dimensional optimization tool to estimate device parameters such as field plate (FP) lengths and FP dielectric thicknesses (td) to maximize the switching figure-of-merit (FoM), BV/RonQg.

A fully integrated 5.9GHz RF frontend in 0.25um GaN-on-SiC for vehicle-to-vehicle applications

This paper presents the design of a high-efficiency and high-power RF frontend for the 802.11p standard, leveraging an embedded Tx/Rx switching scheme and a dual-bias power amplifier (PA) linearization technique. The fully integrated RF frontend is fabricated in 0.25um GaN-on-SiC technology and occupies 2mm × 1.2mm. In the Tx mode, the PA+Tx switch achieves 48.5% drain efficiency at 33.9dBm Psat with 28V supply. With OFDM-modulated signals, it achieves 30% average efficiency at 27.8dBm output power while meeting the -25dB EVM limit without predistortion. In the Rx mode, the LNA+Rx switch achieves +22dBm OIP3 with 8dB power gain at 12V supply. The fully integrated high-efficiency and linear RF frontend is demonstrated at high output power for vehicular communications for the first time.

Study of RF-circuit linearity performance of GaN HEMT technology using the MVSG compact device model

This study is a first demonstration of the use of a physical compact model as a tool to identify technology bottlenecks to the linearity performance of emerging devices such as GaN HEMTs and to provide solutions to improve linearity both through device-design and circuit-design techniques. GaN-based HEMTs are emerging as key technology solutions in wireless communication systems that can address the increasing demand for highly efficient, linear amplification of digitally modulated information to cater to new applications such as personal communication, internet of things, 5G etc [1]. The primary advantage of GaN-HEMTs in terms of higher bandgap, carrier-mobility and charge-density can yield better output power (Pout), and power-added-efficiency (PAE) but the linearity behavior of GaN-based power amplifiers (PAs) that trades-off with the aforementioned figures of merit (FoMs) is still to be understood. Non-linearity results in adjacent channel interference, spectral regrowth, and degrading error vector magnitude (EVM) that impose bandwidth constraints and higher bit error rate (BER) for complex modulated signals.