Third-order Intermodulation Research Articles

A computational approach to optimize the linearity in dual-gate InAlGaN/AlN/GaN HEMTs

Abstract This paper investigates the effect of the proposed dual gate structures in enhancing the linearity of InAlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) using TCAD analysis. Through the comprehensive analysis of the dual gate structure with the additional gate placed between the gate–source (DG-GS) and gate–drain (DG-GD) regions, the impact on the linearity performance has been compared with that of a standard single gate (SG) structure. The dual gate configuration exhibits a flatter and broader transconductance (g m) profile than the SG configuration. The reduction in the third-order intermodulation levels is confirmed with the polynomial fitting method. The f T/f max of the DG-GS case is simulated to be 52/102 GHz, which shows that such configuration does not deteriorate the RF performance. Comprehensive simulations are carried out to study the device physics and assess the mechanism behind the linearity improvement. The large signal model has been developed to examine the large signal RF performance as well as linearity performance metrics. An improvement of 9.6 dB in the carrier-to-intermodulation (C/I) ratio and that of 2.4 degrees in the amplitude-to-phase modulation at 6 dB backoff from P sat have been observed as compared to the SG configuration. Such characteristics have evidenced that the optimized dual-gate configuration with the second gate placed between the source and gate can effectively improve the linearity performance of the InAlGaN/AlN/GaN HEMT configurations.

Understanding and Quantifying the Benefit of Graded Aluminum Gallium Nitride Channel High-Electron Mobility Transistors

Graded AlGaN channel High-Electron Mobility Transistor (HEMT) technology is emerging as a strong candidate for millimeter-wave applications, as superior efficiency and linearity performances can be achieved. In this paper, graded channel AlGaN/GaN HEMTs are investigated with the aim of further understanding the benefit of the graded AlGaN channel compared to more conventional GaN channel HEMTs. Our study employed a comprehensive simulation workflow including an extensive calibration of direct current (DC), S-parameter, large signal, and linearity characteristics at 30 GHz. Through device modeling and implementation of circuit-level simulation using Advanced Design System (ADS, 2023) software, both linearity and large signal performances could be mimicked remarkably. In agreement with previous studies, the results show that graded channel technology allows for a modified electron confinement leading to a 3D electron gas (3DEG). Consequently, the electric field peak inside of the channel is reduced without degrading the radio frequency (RF) performance, as the electron velocity is improved, thus offering a more linear transconductance and better linearity performances. As a result, for graded AlGaN channel HEMTs, a 6 dB output power back-off from peak power-added efficiency (PAE) is needed to achieve a carrier with a third-order intermodulation (C/IM3) ratio of 30 dBc against 9 dB for conventional AlGaN/GaN HEMTs with a lower associated PAE.

High-Linearity Dual-Parallel Mach–Zehnder Modulators in Thin-Film Lithium Niobate

Microwave photonic (MWP) systems are inseparable from conversions of microwave electrical signals into optical signals, and their performances highly depend on the linearity of electro-optic modulators. Thin-film lithium niobate (TFLN) is expected to be an ideal platform for future microwave photonic systems due to its compact size, low optical loss, linear electro-optic effect, and high bandwidth. In this paper, we propose a TFLN modulator with a low voltage–length product (VπL) of 1.97 V·cm and an ultra-high-linearity carrier-to-distortion ratio (CDR) of 112.33 dB, using a dual-parallel Mach–Zehnder interferometer configuration. It provides an effective approach to fully suppress the third-order intermodulation distortions (IMD3), leading to 76 dB improvement over a single Mach–Zehnder modulator (MZM) in TFLN. The proposed TFLN modulator would enable a wide variety of applications in integrated MWP systems with large-scale integration, low power consumption, low optical loss, and high bandwidth.

A study on GaN-based high-efficiency class E power amplifier circuits at medium-low frequencies

Abstract In this paper, a high-power amplifier is designed to address the challenges of low transmission power and poor efficiency in wireless energy transmission technology at low frequencies. The design is based on a class E power amplifier circuit. The theoretical analysis is conducted to determine transistor selection and the static DC operating point. Load traction technology is employed to match the load impedance of the power amplifier, ensuring highly efficient and unified power additional efficiency, and output power. To enhance system stability and feedback compensation, gate series resistance and parallel capacitors are incorporated. Simulation results demonstrate that the designed power amplifier achieves an output power of 48 dBm with a power additive efficiency (PAE) of 85%. Furthermore, the third-order intermodulation component reaches 70 dBm, indicating concentrated output energy and high linearity in the amplifier system. Experimental results validate the consistency between theoretical analysis and model simulation, confirming the stability of the designed power amplifier circuit, and successfully achieving energy-efficient, high-power transmission.

Characterizing third-order intermodulation distortion of photodetectors based on de-coupling and de-embedding modulation distortion of modulators

A novel, to the best of our knowledge, electro-optical modulation method is proposed for measuring third-order intermodulation distortion of photodetectors (PDs) based on de-coupling and de-embedding modulation distortion of modulators. The method utilizes dual parallel intensity modulation to generate electro-optical stimulus signals with fast and fine sweeping capability, and it eliminates the nonlinear impact of modulators by using low-frequency bias swing, allowing a direct extraction of the third-order output intercept point (OIP3) of PD from the combined nonlinear response contributed by both the modulators and the PD. The OIP3 of PD is frequency-swept measured with our method and compared to those with the conventional method to check for consistency. The proposed method enables a modulator-distortion-free, fast, and fine sweeping measurement of PDs using a simple system.

Investigating the effect of scaling and temperature on the performance of improved junctionless nanowire FET through simulation analysis

An Improved Junctionless Nanowire Field Effect Transistor (I-JL-NWFET) device is proposed in this paper to address the limitations of conventional JL-NWFET. This research paper initially, comprehensively analyzes the impact of channel length (L) and channel thickness (t si ) scaling on the electrical, analog/RF, and linearity performance of I-JL-NWFET and JL-NWFET. The results suggest that the specific design features in I-JL-NWFET contribute to a more robust and less sensitive response to variations in scaling compared to its counterpart, JL-NWFET. Furthermore, an exploration into the impact of temperature on the electrical, analog/RF, and linearity performance is also conducted for both I-JL-NWFET and JL-NWFET. The electrical performance of I-JL-NWFET showcases a significantly reduced temperature sensitivity in parameters like drain current (I D ), Subthreshold Slope (SS) and Drain Induced Barrier Lowering (DIBL) compared to JL-NWFET. Subsequently, analyzing the analog/RF performance in the context of parameters such as transconductance (g m ), Transconductance Gain Factor (TGF), output conductance (g d ), early voltage (V EA ), total gate capacitance (C GG ), and cut-off frequency (f T ) under temperature variation, a lower degree of variability in I-JL-NWFET is observed compared to JL-NWFET. Furthermore, the linearity performance of I-JL-NWFET, assessed through parameters such as second and third-order transconductance (g m2 , g m3 ), second and third-order input voltage intercept points (VIP2, VIP3), and third-order intermodulation distortion (IIP3 and IMD3) is improved at the higher temperature than that of JL-NWFET.

AI-DRIVEN TRANSFORMER NETWORKS IN SHARED SPECTRUM FOR ENHANCED SIGNAL PROCESSING FOR NONLINEAR RECEIVERS

Communication systems face challenges from high-power adjacent channel signals, or blockers, inducing nonlinear behavior in RF front ends. Ensuring robust performance in the presence of blockers is crucial for IoT and other spectrum-consuming devices coexisting with advanced transceivers. This paper proposes a flexible, data-driven solution using a Deep Belief Network (DBN) to mitigate third-order intermodulation distortion (IMD) during demodulation. Numerical evaluations of AI-enhanced receivers employing DBN as an IMD canceler and demodulator show significant improvements in bit error rate (BER) performance. The effectiveness of DBN varies with RF front end characteristics, notably the third-order intercept point (IP3).

Design of a Millimeter-Wave Broadband Linearizer Based on an Extended Design Space

In this study, a broadband linearizer design method based on an extended design space is proposed to optimize the design complexity and linearization performance of conventional linearizers for broadband operation. The gain characteristics of the power amplifier (PA) and linearizer are fitted to simplify the analyses and to quickly derive the ideal objective function of the linearizer design. Then, the 1 dB compression point of a nonlinear system is redefined and used to further extend the design space of the linearizer. To verify the proposed design method, a millimeter-wave linearizer prototype based on the extended design space was designed and fabricated. The linearizer was tested with continuous-wave and 100 MHz two-tone signals from 40 GHz to 43 GHz. The measurement results of the linearized PA showed that the output 1 dB power point (OP1dB) was improved by more than 1.7 dB, the phase error was reduced by more than 15°, and the third-order intermodulation distortion (IMD3) was suppressed by 8.6 dB–13.1 dB over the working frequencies. The proposed linearizer achieved good linearization performance, low power consumption, and simple design implementation, and it was not necessary to tune the bias during broadband operation, making it applicable in complex communication scenarios.

Transmit-isolating photonic receivers with high isolation, large dynamic range based on reverse single-sideband modulation

Two kinds of transmit-isolating photonic receiver (TIPRx) systems with high isolation, large dynamic range based on reverse single-sideband (SSB) modulation are proposed and demonstrated. For the single dual-drive modulator (DD-MZM), the transmit signal allows less leakage of the RF power to the PD compared with the reverse double-sideband (DSB) modulation, thanks to the reduction in the number of the sidebands beating with the center carrier, while the forward DSB modulation benefits the high-quality response of the receive signal. Experimental results demonstrate that the average isolation is increased by 3–4 dB through suppressing the sideband intensity of the counter-propagation modulation, and the system has an isolation greater than 15 dB within 4–24 GHz. In addition, the spurious-free dynamic range (SFDR) of 98.31 dB·HZ2/3 is achieved. The parallel DD-MZMs scheme is put forward to improve the isolation and SFDR simultaneously, through the accurate cancellation of the reverse sidebands and third-order intermodulation (IMD3) components. The simulation result proves that the parallel architecture can suppress the reverse response and IMD3 effectively, and has the null of 0.10 for the isolation and the null of 0.20 for the IMD3 components when the optical power ratio is 0.9. The proposed technique can find applications in analog and digital communication.

On the improved RF performance of step field plate LDMOS transistor

This paper presents an analysis of the Step Field Plate Laterally Diffused Metal Oxide Semiconductor (SFP LDMOS) structure for improved high power and RF performance. The proposed structure is cost-effective, CMOS integrable, and has a high power figure of merit (FoM) due to its high off-state breakdown voltage (BVDS,off) and low specific on-resistance (Rsp). Significant improvement in frequency behavior is observed, as demonstrated by the flatter trans-conductance (gm), 12.5x lower gate-to-drain capacitance (Cgd), 2.5x lower gate-to-source capacitance (Cgs), and lower output conductance (gds). Single tone and double tone analyses are performed on an RF PA circuit implemented in TCAD. Results show ∼5 dBm higher output power (Pout), ∼6 dB higher power gain, and 46% higher drain efficiency (η), which are attributed to ∼1.9x lower drain-to-source capacitance (Cds) and ∼15 dBm lower magnitude of third-order intermodulation distortion due to lower third order derivative of drain current (ID). The paper also explains the device physics behind these observations.

Catalyzing satellite communication: A 20W Ku-Band RF front-end power amplifier design and deployment.

This paper presents a groundbreaking Ku-band 20W RF front-end power amplifier (PA), designed to address numerous challenges encountered by satellite communication systems, including those pertaining to stability, linearity, cost, and size. The manuscript commences with an exhaustive discussion of system design and operational principles, emphasizing the intricacies of low-noise amplification, and incorporating key considerations such as noise factors, stability analysis, gain, and gain flatness. Subsequently, an in-depth study is conducted on various components of the RF chain, including the pre-amplification module, driver-amplification module, and final-stage amplification module. The holistic design extends to the inclusion of the display and control unit, featuring the power-control module, monitoring module, and overall layout design of the PA. It is meticulously tailored to meet the specific demands of satellite communication. Following this, a thorough exploration of electromagnetic simulation and measurement results ensues, providing validation for the precision and reliability of the proposed design. Finally, the feasibility of that design is substantiated through systematic system design, prototype production, and exhaustive experimental testing. It is noteworthy that, in the space-simulation environmental test, emphasis is placed on the excellent performance of the Star Ku-band PA within the 13.75GHz to 14.5GHz frequency range. Detailed power scan measurements reveal a P1dB of 43dBm, maintaining output power flatness < ± 0.5dBm across the entire frequency and temperature spectrum. Third-order intermodulation scan measurements indicate a third-order intermodulation of ≤ -23dBc. Detailed results of power monitoring demonstrate a range from +18dBm to +54dBm. Scans of spurious suppression and harmonic suppression, meanwhile, show that the PA evinces spurious suppression ≤ -65dBc and harmonic suppression ≤ -60dBc. Rigorous phase-scan measurements exhibit a phase-shift adjustment range of 0° to 360°, with a step of 5.625°, and a phase-shift accuracy of 0.5dB. Detailed data from gain-scan measurements show a gain-adjustment range of 0dB to 30dB, with a gain flatness of ± 0.5dB. Attenuation error is ≤ 1%. These test parameters perfectly align with the practical application requirements of the technical specifications. When compared to existing Ku-band PAs, our design reflects a deeper consideration of specific requirements in satellite communication, ensuring its outstanding performance and uniqueness. This PA features good stability, high linearity, low cost, and compact modularity, ensuring continuous and stable power output. These features position the proposed system as a leader within the market. Successful orbital deployment not only validates its operational stability; it also makes a significant contribution to the advancement of China's satellite PA technology, generating positive socio-economic benefits.

Mathematical modeling of microwave channels of a semi-active radar homing head

Objectives. Radar homing heads of guided missiles form a large group of radars which differ from other radars due to their specific purpose. The advantages of a semi-active radar homing head (SARH) include the ability to have a powerful irradiator at the command post and, as a result, a powerful reflected signal from the target. This results in an increase in the range of its detection and guidance. The absence of an emitter simplifies the missile’s onboard control equipment, reduces its weight and dimensions, thereby improving its maneuverability and increasing the guidance accuracy, resulting in the greatest distribution of this type of SARH. However, in order to determine the exact Doppler shift of the target signal as part of SARH, a reference signal with a frequency coinciding with the illumination transmitter signal must be supplied to the receiving path. This study aims to synthesize and analyze the SARH receiver circuit with improved accuracy characteristics.Methods. The following methods are used: statistical radio engineering; optimal signal reception theories; and computer modeling in CAD AWR Design Environment.Results. A mathematical model of the SARH receiver was obtained and analyzed. The proposed receiver model allows the spectral characteristics of signals to be calculated at any point of the microwave paths, as well as signal characteristics at the input of the head channel, at the output of the first conversion mixer, at the output of the first intermediate frequency selector, and at the output of the receiving path. The calculated values of the main characteristics of high-frequency channels are also given.Conclusions. The resulting model allows the frequency dependencies of main parameters of the receiving path, such as the gain factor, noise factor, decibel compression points, and third-order intermodulation intercept points to be estimated. The values obtained during the simulation are maximally close to existing systems, since the models of real-life and mass-used microcircuits thu created are used as the main elements when designing high- frequency paths. The model can be used to study methods of improving technical indicators, as well as to develop new principles and schemes for developing radioelectronic complexes, for example, when designing a receiving path using advanced radio photonics.

Multi-Channel Nonlinearity Mitigation Using Machine Learning Algorithms

This paper investigates multi-channel machine learning (ML) techniques in the presence of receiver nonlinearities and noise, and compares the results with the single-channel receiver architecture. It is known that the multi-channel architecture relaxes the sampling speed requirement of analog to digital conversion and provides significant robustness to clock jitter and front-end noise due to the bandwidth-splitting property inherent in these receivers. However, when a high-voltage swing signal is used in a wireline communication link, the received signal suffers from third-order harmonic distortions and inter-modulation products caused by the nonlinearity profile of the analog front-end (AFE). To this end, this paper proposes the channel decision passing (CDP) algorithm in combination with nonlinear feedback cancellation as a low-complexity candidate for nonlinearity mitigation and compares the performance of this solution with other well-known ML algorithms. Simulation results show significant improvement in a multi-channel receiver architecture equipped with nonlinear feedback cancellation and CDP in comparison with its single-channel counterpart under practical nonlinearity profiles and noise conditions.

Nonlinear Capacitance Compensation Method for Integrating a Metal–Semiconductor–Metal Varactor with a Gallium Nitride High Electron Mobility Transistor Power Amplifier

A nonlinear capacitance compensation technique is presented in this paper to enhance the linearity of a power amplifier (PA) in the GaN process. The method involves placing an MSM varactor device alongside the GaN HEMT device, which works as the amplifying unit such that the overall capacitance observed at the amplifier input is constant, thus improving linearity. This approach is a reliable and straightforward way to improve PA linearity in the GaN process. The proof-of-concept prototype in this study involves the fabrication of a PA device using a standard GaN HEMT process, which successfully integrates the proposed compensation technique and demonstrates excellent compatibility with existing processes. The prototype has a saturation output power of 18 dBm, a peak power-added efficiency of 51.8%, and a small signal gain of 15.5 dB at 1 GHz. The measured AM–PM distortion at the 5 dB compression point is reduced by more than 50% compared to that of an uncompensated device. Furthermore, the results of third-order intermodulation distortion demonstrate the effectiveness of the linearity enhancement concept, with values improved by more than 5 dB in the linear region compared to those of the uncompensated device. All of the results demonstrate the potential utility of this design approach for wireless communication applications.

A Dual-Mode CMOS Power Amplifier with an External Power Amplifier Driver Using 40 nm CMOS for Narrowband Internet-of-Things Applications

The narrowband Internet-of-Things (NB-IoT) has been developed to provide low-power, wide-area IoT applications. The efficiency of a power amplifier (PA) in a transmitter is crucial for a longer battery lifetime, satisfying the requirements for output power and linearity. In addition, the design of an internal complementary metal-oxide semiconductor (CMOS) PA is typically required when considering commercial applications to include the operation of an optional external PA. This paper presents a dual-mode CMOS PA with an external PA driver for NB-IoT applications. The proposed PA supports an external PA mode without degrading the performances of output power, linearity, and stability. In the operation of an external PA mode, the PA provides a sufficient gain to drive an external PA. A parallel-combined transistor method is adopted for a dual-mode operation and a third-order intermodulation distortion (IMD3) cancellation. The proposed CMOS PA with an external PA driver was implemented using 40 nm-CMOS technology. The PA achieves a gain of 20.4 dB, a saturated output power of 28.8 dBm, and a power-added efficiency (PAE) of 57.8% in high-power (HP) mode at 920 MHz. With an NB-IoT signal (200 kHz π/4-differential quadrature phase shift keying (DQPSK)), the proposed PA achieves 24.2 dBm output power (Pout) with a 31.0% PAE, while satisfying −45 dBc adjacent channel leakage ratio (ACLR). More than 80% of the current consumption at 12 dBm Pout could be saved compared to that in HP mode when the proposed PA operates in low-power (LP) mode. The implemented dual-mode CMOS PA provides high linear output power with high efficiency, while supporting an external PA mode. The proposed PA is a good candidate for NB-IoT applications.

The Optimal Operating Point for Linearizing an Integrated Optical Lithium Niobate Directional Coupler Modulator

The influence of an operating point on the linearity of an integrated optical lithium niobate directional coupler modulator was studied. It was found that the optimal setting for the position of an operating point for suppressing the third-order intermodulation distortion depended on the power of the high-frequency modulation signal. Thus, despite the simple design of the device, the directional coupler modulator requires a complex algorithm for setting an operating point to achieve a high linearity of operation. An active system for setting an operating point based on the low-frequency pilot signal and zeroing its third harmonic was used to demonstrate the possibility of linearization when the amplitude of the modulation signal changes. The use of an operating point control system became possible after limiting the drift of the operating point by etching the dielectric buffer layer in the interelectrode gap. The results obtained look promising for high-performance analog optical links.

An Ultra-wideband Low-power Low-noise Amplifier Linearized by Adjusted Derivative Superposition and Feedback Techniques

Ultra-wideband (UWB) applications require low-power and low-noise amplifiers (LNAs) that can operate over a wide frequency range. However, conventional LNAs often suffer from poor linearity and high-power consumption. This research work proposes a novel LNA design that uses the adjusted derivative superposition (DS) technique and feedback to improve the linearity and reduce the power consumption of UWB LNAs. The DS technique enhances the third-order intermodulation (IM3) cancellation by adjusting the bias currents of the transistors, whereas the feedback improves the stability and input matching of the LNA. The LNA is implemented using a degenerated common source topology in a 180 nm standard CMOS technology. The simulation results show that the LNA achieves a power gain of 10–12.2 dB, an input third-order intercept point (IIP3) of about 12 dBm, and a noise figure of less than 2.5 dB over the UWB frequency band of 3.1–10.6 GHz. The input reflection coefficient is less than -10 dB, and the power consumption is 11.6 mW with a 1.5 V power supply. The designed LNA offers a novel and innovative solution for UWB applications that significantly improve the performance and efficiency of UWB LNAs whereas reducing the cost and complexity of implementation.

Multichannel Microwave Photonic Phase Shifter With Improved Power Efficiency and Suppressed Third-Order Intermodulation Distortions

Multichannel Microwave Photonic Phase Shifter With Improved Power Efficiency and Suppressed Third-Order Intermodulation Distortions

Tackling third-order intermodulation distortion: modeling and analysis of linearized RoF link for future perspective networks

Tackling third-order intermodulation distortion: modeling and analysis of linearized RoF link for future perspective networks

Impact of Source Resistance on Linearity of AlGaN/GaN HEMTs at Ka-Band

The impact of the source resistance (RS) on the linearity of AlGaN/GaN high electron mobility transistors (HEMTs) measured by the two-tone test is investigated in this study. The theoretical analysis of the third-order intermodulation (IM3) and the third-order intercept point (IP3) of the devices was performed based on the equivalent circuit approach and the polynomial curve fitting technique. The results revealed that the suppression of IM3 level and thus the improvement of IP3 were achieved for the device with a larger RS. For the experimental verifications, three types of AlGaN/GaN HEMTs were fabricated with different layout structures and air-bridge architectures corresponding to different RS values, which were then extracted by the cold-FET method. It is concluded that a device with a shorter length of middle source pad (LMS) and a side-type air-bridge architecture tends to have a larger RS value. In this study, the 4 × 50–20 device with LMS of 20 um and a side-type air-bridge architecture demonstrated the best-measured linearity performance at 30 GHz due to the largest RS.