Quadrature Signals Research Articles

Phase-Locked Loop Independent Second-Order Generalized Integrator for Single-Phase Grid Synchronization

Second-order generalized integrator (SOGI) requires fast and accurate grid voltage frequency information for quadrature signal generation (QSG) in single-phase systems. Conventionally, synchronous reference frame phase-locked loop (PLL) (SRFPLL) is used in a cascade manner and provides frequency feedback to SOGI. PLL is a non-linear closed-loop control system that requires adequate gain parameter design trade-off to provide accurate grid synchronization. Additionally, it creates interdependent loops while estimating the grid frequency and phase-angle. This results in unwanted frequency disturbances during grid transients, such as voltage sag and phase-angle jumps (PAJs) which are fed back to the SOGI as well. Thus, this article proposes two PLL independent frequency-feeding approaches for SOGI: Type-A and -B. The frequency is estimated using the normalized single-phase grid voltage signal in both types. In Type-A, the normalization is done using cascaded recursive discrete-Fourier transform (RDFT) and inverse RDFT (IRDFT). On the other hand, in Type-B, SOGI outputs are used for normalization. The grid voltage amplitude is estimated using the absolute value of the in-phase and in-quadrature components of the proposed frequency-adaptive SOGI. Furthermore, the third-order polynomial approximation of the arctangent function is implemented for phase-angle estimation in both types. The performance of both the types during transients and steady-state grid voltage disturbances (dc offset and harmonics) are compared with SOGIPLL using both simulations and experiments.

A Mechatronic Lock-In Amplifier: Integrating Demodulation in Sensor Electronics for Measuring Mechanical Oscillations

The demodulation of mechanical oscillations is essential for the operation of micro- and nanometer-scale transducer systems, such as resonant MEMS mirrors and cantilever-based sensors. The use of external demodulators, such as lock-in amplifiers and spectrum analyzers is not always desired due to their large size, complexity, and cost. The method presented in this article enables simplified demodulation of the oscillation of mechanical oscillators with integrated deflection sensors. By configuring two deflection sensors in separate bridge circuits, which are supplied with in-phase and quadrature sinusoidal signals, the amplitude, and phase of the mechanical oscillation can directly be measured without additional demodulation. The method is implemented and experimentally verified by demodulating the oscillation of a self-sensing Atomic Force Microscopy cantilever with integrated piezoresistive elements.

Метод проектирования широкополосного формирователя квадратурных сигналов

There are certain difficulties in the development of a broadband generator of quadrature signals (QSG) on a SiGe BiCMOS technology. The problem of linearity and broadband matching is the most difficult to solve. When designing QSG in a wide frequency band, there is a problem of forming a quadrature signal using traditional solutions using a polyphase filter or a digital D-trigger. The use of only one method for forming a quadrature signal is impossible due to the limiting features of the electronic component base of SiGe BiCMS technology. To solve this problem, we propose a structure that allows us to develop a broadband quadrature signal generator with an operating frequency range from 10 MHz to 6 GHz, using the method of dividing the operating frequency band. At frequencies from 1 to 6 GHz, the quadrature signal is generated using a polyphase filter, and at frequencies less than 1 GHz using a frequency divider. Using this method, the following characteristics of the FCS have been achieved: the difference in the amplitudes of quadrature signals is less than 0.3 dB; the VSWR is less than 1.6 over the entire frequency range; the transmission coefficient is not less than -2 dB at a 0 dBm heterodyne power; at a frequency of 6 GHz P1dB of at least 3 dBm. The experimental results are in good agreement with the simulation data.

Evaluation of Quadrature Signal Generation Methods with Reduced Computational Resources for Grid Synchronization of Single-Phase Power Converters through Phase-Locked Loops

Low-cost single-phase grid connected converters require synchronization with the grid voltage to obtain a better response and protection under diverse conditions, such as frequency perturbations and distortion. Phase-locked loops (PLLs) have been used in this scenario. This paper describes a set of quadrature signal generators for single-phase PLLs; compares the performances by means of simulation tests considering diverse operation conditions of the electrical grid; proposes strategies to reduce the computational burden, considering fixed-point digital implementations; and provides both descriptive and quantitative comparisons of the required mathematical operations and memory units for implementation of the analyzed single-phase PLLs.

Analytical evaluation of equivalent energy loss in causal frequency selection filters in the processing of quadrature amplitude modulation signals

In this paper, we consider the need to assess the influence of the parameters of a linear time-invariant causal system in the processing of quadrature amplitude modulation signals of various positionality and constellation diagram irregularity. We describe the equations that determine the energy balance of a radio line and the total losses arising in route. We have developed mathematical expressions to assess the equivalent energy losses caused by the irregularity of amplitude-frequency and phase-frequency characteristics of the frequency selection filters. We propose a procedure to assess the non-noise losses in the frequency selection filters when designing high-speed radio systems for transmitting the information.

Design & development of 140 GHz D-band phase locked heterodyne interferometer system for real-time density measurement

A 140 GHz phase-locked heterodyne interferometer system has been designed, developed and installed at Aditya Tokamak for real time density measurement. The interferometer uses a novel approach of zero-cross detection using in-phase and quadrature (IQ) signals with a single balanced mixer. The transmitter and receiver systems are phase locked by a 100 MHz crystal oscillator and the output signals are mixed in a single balanced mixer which produces highly stabilized intermediate frequency (IF) frequency of 2.0 GHz. This signal is further amplified by low noise amplifier (LNA) and power amplifier with built-in automatic gain control (AGC) of response time 5 ms. The AGC keeps the IF signal amplitude stable for 20–70 dB attenuation. This IF signal is further down converted to 100 KHz IQ signals using a synthesizer which is phase locked by the same 100 MHz crystal oscillator used for phase locking the transmitter and receiver oscillators. The 100 KHz IQ signals are digitized by built-in 12 bits ADCs and processed though FPGA programming for real time phase-density calculations. The developed system has minimum phase sensitivity of 0.07 radian and a time resolution of 5 μs with 10 KHz resolution for real time density measurement. The density evolution of plasma discharge and effect of gas puff on density built up is successfully measured in real time and presented in this paper.

A 2.4-㎓ Low-power Low-IF Receiver Employing a Quadrature Low-noise Amplifier for Bluetooth Low Energy Applications

In this paper, a low-power low-IF receiver employing a quadrature low-noise amplifier (LNA) is proposed for Bluetooth low energy (BLE) applications. The proposed quadrature LNA, which can provide accurate quadrature signals in the RF path, consists of a common-source amplifier with inductive degeneration and a quadrature generator based on a common-gate amplifier with a single RC network. Therefore, a BLE receiver using the proposed LNA can eliminate quadrature generating circuitry of the LO chain, thereby reducing power consumption. The implemented receiver is composed of the quadrature LNA, single-to-differential double-balanced active mixer, and second-order G<SUB>m-</SUB>C complex filter. Simulated in a 65-nm CMOS process, it achieves a conversion gain, noise figure, and an image rejection ratio of 53.2 dB, 4.81 dB and 38 dB, respectively, and consumes 2.2 mA from a supply voltage of 0.8 V. The die area is 2.24 ㎟.

Robust Frequency Cascaded Adaptive Complex Filter Control for Grid Interactive PV System

This article deals with a robust frequency cascaded adaptive complex filter (ACF) control for the grid interactive photovoltaic (PV) system. The incorporated control algorithm rejects lower order harmonics too unlike the conventional quadrature signal generators; thus, this control algorithm extracts accurate fundamental frequency orthogonal components of load current. The voltage source converter (VSC) acts as a distribution static compensator (DSTATCOM) when generation from the PV array is unavailable, besides injecting active power in the distribution network, and reducing reactive power loading on the utility network by mitigating harmonics in presence of generation from the PV array. Thus, the VSC utility is enhanced. This PV system performance is robust against the weak utility grid parameter variation and at load perturbation. The presented algorithm improves transient response at dynamic loading and irradiance change. The harmonic contents in distribution network voltage and utility current are reduced within the IEEE-519 standard.

Efficiency of adaptive filter with envelope tracking algorithm when receiving signals with multi-position PSK against the background of non-fluctuation interferences

The energy and spectral advantages of signals with phase-shift keying predetermined their widespread use in modern digital navigation, communications and television systems. The use of this type of signal in a multi-position format with an increased number of possible phase states allows increasing the information capacity of the channel signal, and consequently the throughput rate of radio channels. The presence of non-fluctuation interference in such radio channels greatly reduces the noise immunity of information reception. A well-known way to deal with such interference is to use adaptive non-recursive filters in the receiver. The article evaluates the effectiveness of using such a filter with an algorithm for setting weight coefficients that controls the constant envelope of a useful signal when receiving signals with multi-position phase shift keying against the background of noise and non-fluctuation interference. Two types of such interference are considered – harmonic and relayed. Using computer simulation, the optimal filter parameters (adaptation coefficient and its length) are determined; the effect of the filter on the noise immunity of the quadrature signal receiver with multi-position phase shift keying for various combinations of interference and their intensity is estimated. It is shown that such an adaptive filter can successfully cope with the most dangerous sighting harmonic interference.

Quadrature phase detection based on an extrinsic Fabry-Pérot interferometer for vibration measurement.

A novel vibration measurement system based on a fiber-optic extrinsic Fabry-Pérot interferometer is established. Two quadrature interferometry signals are obtained in accordance with the 90° phase shift between two output arms of a 2×2 fiber coupler. This outcome drastically simplifies the processing of collected data because only a single arctangent operation is needed to calculate the wrapped phase. Repetitive test results show that the relative micro-vibration reconstruction error of this method is less than 0.12%. This structure simplifies the extrinsic Fabry-Pérot signal demodulation process, which has guiding significance for the online measurement of high-precision physical quantities.

High Performance Circularly Polarized MIMO Antenna with Polarization Independent Metamaterial

This paper presents a high performance circularly polarized multiple input multiple output microstrip patch antenna which is suitable for current high data rate requirements. Circular polarization has been achieved by dual feeding the signals in phase quadrature to the patch antenna. A polarization independent metamaterial has been designed. The designed metamaterial is used to enhance the gain of the antenna and used as a superstrate of this patch antenna. Using metamaterial superstrate, a gain as high as 13.6 dBi with a bandwidth of 15.4% has been achieved at 11 GHz. The structure has been fabricated and the simulated results are in good agreement with the measured results. Circular polarized antenna also reduces the delay spread due to multipath environment and provides high latency.

Generative adversarial network-based electromagnetic signal classification: A semi-supervised learning framework

Generative adversarial network (GAN) has achieved great success in many fields such as computer vision, speech processing, and natural language processing, because of its powerful capabilities for generating realistic samples. In this paper, we introduce GAN into the field of electromagnetic signal classification (ESC). ESC plays an important role in both military and civilian domains. However, in many specific scenarios, we can't obtain enough labeled data, which cause failure of deep learning methods because they are easy to fall into over-fitting. Fortunately, semi-supervised learning (SSL) can leverage the large amount of unlabeled data to enhance the classification performance of classifiers, especially in scenarios with limited amount of labeled data. We present an SSL framework by incorporating GAN, which can directly process the raw in-phase and quadrature (IQ) signal data. According to the characteristics of the electromagnetic signal, we propose a weighted loss function, leading to an effective classifier to realize the end-to-end classification of the electromagnetic signal. We validate the proposed method on both public RML2016.04c dataset and real-world Aircraft Communications Addressing and Reporting System (ACARS) signal dataset. Extensive experimental results show that the proposed framework obtains a significant increase in classification accuracy compared with the state-of-the-art studies.

An Optimized Design Method of PSWFs Pulse Group Based on DFT Precoding

Aiming at the problems of non-sinusoidal time-domain multiple quadrature modulation signals based on Prolate Spheroidal Wave Functions (PSWFs), as the number of pulses increases, the bandwidth efficiency of the modulation signal frequency band decreases, the Peak-to-Average Power Ratio (PAPR) and the implementation complexity are high, a method for optimal design of PSWFs pulse groups based on DFT precoding is proposed. The PSWFs pulse signal frequency domain generation method is adopted. By introducing the precoding matrix, the multi-channel PSWFs pulse group signals are optimized and designed, and then the input data is redistributed to obtain new PSWFs pulse group signals. Experimental results show that this method can further improve the power efficiency of the modulated signal and effectively reduce the peak-to-average power ratio of the modulated signal without changing the orthogonality of the original PSWFs subcarriers. As the number of carriers increases, the suppression effect on the peak-to-average power ratio becomes more obvious.

Digital Demodulation Using I/Q Signals and Optical Phase Control Applied to a Vibrometer

An efficient and cost effective optical phase detection vibrometer based on a modified closed loop homodyne Michelson interferometer is presented. Real-time phase demodulation is carried out, using an embedded platform that performs data acquisition, signal processing, PI (proportional-integral) control and the generation of signals that drive the electrooptic Pockels cell phase shifter and the piezoelectric actuator under test. Two phase quadrature signals are generated from a single interferometric output, using the interleaving action, in alternation, of a digitally generated modulating signal, and then the well-known differential-cross-multiplication technique is applied to perform the computation of the phase shift of interest. The quadrature condition is reached using the PI loop based on an error signal obtained from a Lissajous figure derived from out-of-phase signals. The vibrometer is capable of measuring nanometric displacements, and is simple, inexpensive, accurate, immune to fading and self-consistent. The new method was used to determine the displacement frequency response curves of two prototypes of multi-actuated flextensional piezoelectric actuators. Measurements were made between 500 Hz and 15 kHz, and the results agreed with those obtained by the standard SCM-Signal Coincidence Method.

Prefiltered Synchronization Structure for Grid-Connected Power Converters to Reduce the Stability Impact of PLL Dynamics

Grid-connected converters under weak grid conditions could present instabilityassociated with the synchronization elements and not directly with the current control loop. The impedance-based stability criterion is an effective tool to address the problem. To solve the negative effect of the synchronous reference frame phase-locked loop (SRF-PLL) on grid current control under weak grid conditions, a synchronization structure with prefilter, based on a filtered quadrature signal generator (FQSG), is proposed in this article to improve the dynamics of the controller’s performance. The small-signal impedance model, implemente as a multiple-input multiple-output system in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -frame, characterizes the effect of the FQSG-PLL dynamics on the current control loop. From it, the impedance-based analysis shows the reduction of the stability issues of the converter. The analysis results were verified by time-domain simulations and by experimental tests in a full-scale 2-MW converter test bench.

Analysis of Inter-Core Crosstalk in Weakly-Coupled Multi-Core Fiber Coherent Systems

The influence of the inter-core crosstalk (ICXT) on the performance of weakly-coupled multi-core fiber (WC-MCF) systems with coherent detection and arbitrary inter-core skew is studied numerically and analytically. We analyze the evolution of the instantaneous ICXT power, induced by polarization division multiplexed quadrature amplitude modulation signals, short term average crosstalk (STAXT), and detected ICXT components along the time to get insight on how the ICXT affects the coherent system performance. Numerical results show that, with low skew-symbol rate product (4:1), the STAXT can have large fluctuations along the time and the variance of the detected ICXT can also have large fluctuations along the time, causing large variations of the bit error rate (BER) along time. With large skew-symbol rate product (≫1), the STAXT is almost constant along the time and, although the detected ICXT varies along time, the detected ICXT variance is almost constant along time leading to very small fluctuations of BER along time. Analytical expressions for the variance of the coherently detected ICXT, average BER and optical signal-to-noise ratio (OSNR) penalty are proposed and shown to agree with Monte-Carlo simulation results for arbitrary skew, modulation format order, and roll-off factor of the transmitted signals. Numerical results show that the maximum allowable ICXT level for 1 dB OSNR penalty increases when the skew augments and can reach 1.3 dB for a roll-off factor of 1. For most cases of interest of low roll-off factor, the increase of the maximum allowable ICXT level is very small. It is shown that the OSNR penalty estimates agree quite well with other authors' experimental results (with nearly zero roll-off factor).

Linear Kalman Filter-Based Grid Synchronization Technique: An Alternative Implementation

Grid synchronization techniques play a significant role in integrating renewable energy sources to the electric power grid. In this context, estimating the phase and frequency of the grid voltage signal is an interesting problem. Out of various techniques available in the literature, linear Kalman filter (LKF) is one of the most popular one. In this article, we propose an alternative implementation of the LKF for grid synchronization application. The proposed implementation uses a linear parametric model of the grid voltage signal including dc offset. It does not involve any quadrature signal generation, rather it works by estimating the phase angle. This helps to estimate the unknown grid frequency directly from the phase angle. This clearly differentiates the proposed alternative implementation with respect to the existing implementations. Performance improvement by the proposed technique is verified extensively through comparative numerical simulation and experimental studies. Comparative results demonstrate the suitability of the proposed technique with respect to other state-of-the-art techniques namely second-order generalized integrator phase-locked loop and enhanced phase-locked loop.

Analysis and design of a new low‐phase noise and Gm‐enhanced class‐C quadrature VCO

This study presents a new low-power and low-phase noise Colpitts quadrature voltage-controlled oscillator (QVCO). The proposed QVCO contains two differential Colpitts voltage-controlled oscillators (VCOs) that use gain-boosting technique to enhance the negative transconductance and relax start-up condition. Both switching and tail transistors are configured in class-C to improve impulse sensitivity function and phase noise performance of the circuit via better noise modulation function. In addition, flicker noise would be reduced because of the switched-biasing mechanism of tail transistors. Phase noise analysis shows that changing the bias voltage of switching as well as tail transistors can improve the phase noise performance of the core VCO with overlap reduction of the transistors active time. Consequently, due to no extra noisy elements for coupling and class-C biasing of all transistors, low-phase noise quadrature signals are generated. To verify the performance of the proposed technique, post-layout simulation is performed in Taiwan Semiconductor Manufacturing Company (TSMC) of 0.18 μm Radio Frequency-Complementary Metal-Oxide- Semiconductor (RF-CMOS) process at a supply voltage of 1.2 V. Post-layout simulation results show that the phase noise of the proposed QVCO is −120.6 dBc/Hz at 1 MHz offset from 5.73 GHz operation frequency. The total power consumption of the QVCO is 3.1 mW and the tuning range is from 5 to 5.73 GHz.

Operation algorithms and application of functional converters modulating voltage for generation of precision radio signals with angular modulation

The article presents a synthesis of algorithms and structures of functional converters modulating voltage for their use as part of quadrature radio signal generators with angular modulation. The study is an alternative method for suppressing spurious amplitude modulation and spurious phase modulation, using controlled spectrum expansion using functional converters modulating voltage. The main requirement for functional converters is the accuracy of representation of the modulating voltage in nonlinear converters by a limited number of terms of Taylor series decompositions that depend on the implemented modulation index. Functional conversion accuracy analysis, spectral analysis and technical implementation of functional converters by table method on the basis of analogue-to-digital converter, permanent memory device and digital-to-analog converter in mode of generation of phase modulation index equal to π are performed.

A 2.4-GHz Quadrature Local Oscillator Buffer Insensitive to Frequency-Dependent Loads for Bluetooth Low Energy Applications

In this letter, a 2.4-GHz quadrature local oscillator (LO) buffer insensitive to frequency-dependent loads is presented for Bluetooth low energy (BLE) applications. An LC tank is used as a load in the proposed buffer to provide a sufficient voltage gain and large voltage swing at the operating frequencies of BLE. Furthermore, the effect of the frequency-dependent impedance of the LC tank on the gain and phase mismatches is reduced by adding compensating transistors. The proposed buffer can provide accurate quadrature signals without additional circuitry in the LO path, minimizing the current consumption of the receiver. It is implemented in 65-nm CMOS technology. It achieved a voltage gain of 5.6 dB, a gain mismatch less than 0.3 dB, a phase mismatch less than 1.1°, and an output ${P} _{{1dB}}$ of 3 dBm. It draws an average current of 3.8 mA from a supply voltage of 0.8 V. The active die area is 0.55 mm2.