[신간안내] Computational Electrodynamics (the finite difference time - domain method)

Characterization and linearization of RF power amplifiers (PAs) are key issues of fifth-generation wireless communication systems, especially when high peak-to-average ratio waveforms are introduced. Recently, deep learning methods have achieved great success in numerous domains including wireless physical-layer. However, there has been limited work in using deep learning for PAs behavioral modeling and linearization. In this paper, we make a bridge between memory effects of the nonlinear PAs and memory of bidirectional long short-term memory (BiLSTM) neural networks. We then build a BiLSTM-based behavioral modeling architecture and its accompanying digital predistortion (DPD) model by reconciling a non causality concern. Next, an additional model is proposed in this paper to mitigate uncertainty of the tested PA when transforming phases. The experimental results demonstrate the effectiveness of the proposed scheme, in which the adequately trained networks are capable of characterizing the PA, and the artificial intelligence-based DPD shows promising linearization performance when considering the tested PAs inherent unpredictability.

Behavioral Modeling and Linearization of Wideband RF Power Amplifiers Using BiLSTM Networks for 5G Wireless Systems

We present terahertz (THz) detectors based on top-gated graphene field effect transistors (GFETs) with integrated split bow-tie antennas. The GFETs were fabricated using graphene grown by chemical vapor deposition (CVD). The THz detectors are capable of room-temperature rectification of a 0.6 THz signal and achieve a maximum optical responsivity better than 14 V/W and minimum optical noise-equivalent power (NEP) of 515 pW/Hz(0.5). Our results are a significant improvement over previous work on graphene direct detectors and are comparable to other established direct detector technologies. This is the first time room-temperature direct detection has been demonstrated using CVD graphene, which introduces the potential for scalable, wafer-level production of graphene detectors.

https://publications.lib.chalmers.se/records/fulltext/202575/local_202575.pdf

Antenna-integrated 0.6 THz FET direct detectors based on CVD graphene.

A review of InP/InAlAs/InGaAs based transistors for high frequency applications

Many emerging applications in the terahertz (THz) frequency range demand highly sensitive, broadband detectors for room-temperature operation. Field-effect transistors with integrated antennas for THz detection (TeraFETs) have proven to meet these requirements, at the same time offering great potential for scalability, high-speed operation, and functional integrability. In this contribution, we report on an optimized field-effect transistor with integrated broadband bow-tie antenna for THz detection (bow-tie TeraFET) and compare the detector's performance to other state-of-the-art broadband THz detector technologies. Implemented in a recently developed AlGaN/GaN MMIC process, the presented TeraFET shows a more than twice performance improvement compared to previously fabricated AlGaN/GaN-HEMT-based TeraFETs. The detector design is the result of detailed modeling of the plasma-wave-based detection principle embedded in a full-device detector model to account for power coupling of the THz radiation to the intrinsic gated FET channel. The model considers parasitic circuit elements as well as the high-frequency impedance of the integrated broadband antenna, and also includes optical losses from a silicon substrate lens. Calibrated characterization measurements have been performed at room temperature between 490 and 645 GHz, where we find values of the optical (total beam power referenced) noise-equivalent power of 25 and ${\text{31 pW}}/\surd{\text{Hz}}$ at 504 and 600 GHz, respectively, in good agreement with simulation results. We then show the broadband detection capability of our AlGaN/GaN detectors in the range from 0.2 to 1.2 THz and compare the TeraFETs’ signal-to-noise ratio to that of a Golay cell and a photomixer. Finally, we demonstrate an imaging application in reflection geometry at 504 GHz and determine a dynamic range of >40 dB.

/pdf/a-high-sensitivity-algan-gan-hemt-terahertz-detector-with-1oky7qtqak.pdf

A High-Sensitivity AlGaN/GaN HEMT Terahertz Detector With Integrated Broadband Bow-Tie Antenna

A broadband and highly efficient class-G supply modulated power amplifier (PA) system with 120-MHz instantaneous modulation bandwidth operating in the 1.8-GHz band is presented in this paper. The core element is the fast class-G supply modulator which switches the supply voltage of the RF PA between three discrete levels with a minimum pulse duration of 2.5 ns. Two designs for the drain bias interface between PA and modulator are evaluated where the best results are achieved for an implementation based on a $\lambda $ /4-wavelength RF-choke. Measurement results are presented for a 120-MHz contiguous carrier aggregated signal using eleven subcarriers with modulation bandwidths ranging from 5 to 20 MHz for each subcarrier. In combination with digital predistortion, the system achieves 38.5% PAE with −40-dB EVM and −46-dB ACLR for the 120-MHz multicarrier signal with a peak-to-average power ratio of 10 dB at the PA output and 39-dBm average output power. The total efficiency enhancement achieved by the class-G modulation is 13% points.

Highly Efficient 1.8-GHz Amplifier With 120-MHz Class-G Supply Modulation

This paper presents a novel InP-SiGe BiCMOS technology using wafer-scale heterogeneous integration. The vertical stacking of the InP double heterojunction bipolar transistor (DHBT) circuitry directly on top of the BiCMOS wafer enables ultra-broadband interconnects with <; 0.2 dB insertion loss from 0-100 GHz. The 0.8 × 5 μm2 InP DHBTs show fT/fmax of 400/350 GHz with an output power of more than 26 mW at 96 GHz. These are record values for a heterogeneously integrated transistor on silicon. As a circuit example, a 164-GHz signal source is presented. It features a voltage-controlled oscillator in BiCMOS, which drives a doubler-amplifier chain in InP DHBT technology.

InP-DHBT-on-BiCMOS Technology With $f_{T}/f_{\max}$ of 400/350 GHz for Heterogeneous Integrated Millimeter-Wave Sources

In this paper, a highly efficient class-G supply modulator targeting high-power wideband envelope tracking applications is presented. The maximum output power using a 50% duty cycle at 100-MHz switching frequency is 62 W for a switching between 30 and 50 V delivered in a 25- $\Omega $ load. The modulator including its driver circuit reaches an overall efficiency in the range of 97%–88% for switching frequencies from dc to 100 MHz for passive loads in a wide range. The modulator is designed to operate at various supply voltage levels and is evaluated within the range from 20 to 50 V while powering loads from 25 to 100 $\Omega $ . The modulator is characterized in terms of efficiency, switching frequency, and nonlinearities.

100-MHz GaN-HEMT Class-G Supply Modulator for High-Power Envelope-Tracking Applications

In this paper, a class-G power amplifier is presented. It consists of a discrete class-G supply modulator, which uses a GaN-HEMT for switching, connected to a 2.65 GHz power amplifier with 40 W peak power, specifically designed for class-G supply modulation. The focus of the paper is on evaluating this system in terms of the RF and the switching signal, the switching behavior, and linearity. A combination of a complex memory polynomial digital predistorter and lookup tables as well as class-G-optimized digital predistorter models is used to improve the linearity of the power amplifier. It is found that the Class-G modulation improves overall PAE by 10–15 %. It is shown that using dedicated digital predistortion the linearity the distortions caused by the modulator can be significantly reduced.

Linearity analysis of a 40 W class-G-modulated microwave power amplifier

A highly efficient three-level class-G modulated RF power amplifier (PA) is presented. The PA is designed to operate as downlink amplifier in the 1800–1900 MHz LTE-band. At 1.85 GHz the maximum output power under continuous wave excitation is 48.2 dBm (66 W). The system achieves an overall efficiency of more than 50% when amplifying a 20 MHz OFDM signal with 9 dB peak-to-average power ratio at 40 dBm (10 W) average output power and over 15 dB gain. In combination with digital predistortion the class-G modulated PA can achieve an ACLR of −36.2 dB and an EVM of 2.1%. The class-G modulation enables excellent efficiency due to absence of a linear amplifier in the modulator stage. The efficiency improvement due to the three-level class-G modulation reaches 18.7 percentage points.

Wolfgang Heinrich

Papers

Highly Efficient 1.8-GHz Amplifier With 120-MHz Class-G Supply Modulation

InP-DHBT-on-BiCMOS Technology With $f_{T}/f_{\max}$ of 400/350 GHz for Heterogeneous Integrated Millimeter-Wave Sources

100-MHz GaN-HEMT Class-G Supply Modulator for High-Power Envelope-Tracking Applications

Linearity analysis of a 40 W class-G-modulated microwave power amplifier

A three-level class-G modulated 1.85 GHz RF power amplifier for LTE applications with over 50% PAE