Loop Noise Research Articles

Howling reduction by analog phase-locked loop and active noise control circuits

This paper proposes a howling reduction circuit using analog phase-locked loop (PLL) and active noise control (ANC) circuits. The proposed circuit reduces howling by generating a signal opposite in phase to howling. To make a signal with the same frequency as howling, we employed the PLL circuit. The ANC circuit was used to control the amplitude of the signal. In addition, we employed pseudo-lock avoidance and differential switch circuits to avoid noise generation. The results confirm the effects of howling reduction by the proposed circuit.

A CMOS Class-D Line Driver Employing a Phase-Locked Loop Based PWM Generator

A Class-D line driver that utilizes a phase-locked loop (PLL) for PWM generation is presented. The principle of operation and implementation details relating to loop stability, linearity and noise performance are analyzed. An implementation is presented in a 130 nm CMOS process. The amplifier can deliver 1.2 W into a 6.8 Ω load with a 4.8 V power supply. The architecture eliminates the requirements for a high-quality carrier generator and a high-speed voltage comparator that are often required in PWM implementations. It can achieve a THD of -65 dB, for a sinusoidal input with a frequency of 60 kHz, while employing a switching frequency that can be as high as 20 MHz. The peak efficiency is 83% for output power larger than 1 W for a switching frequency of 10 MHz. The die area is 2.25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Noise performance of frequency modulation Kelvin force microscopy

Noise performance of a phase-locked loop (PLL) based frequency modulation Kelvin force microscope (FM-KFM) is assessed. Noise propagation is modeled step by step throughout the setup using both exact closed loop noise gains and an approximation known as “noise gain” from operational amplifier (OpAmp) design that offers the advantage of decoupling the noise performance study from considerations of stability and ideal loop response. The bandwidth can be chosen depending on how much noise is acceptable and it is shown that stability is not an issue up to a limit that will be discussed. With thermal and detector noise as the only sources, both approaches yield PLL frequency noise expressions equal to the theoretical value for self-oscillating circuits and in agreement with measurement, demonstrating that the PLL components neither modify nor contribute noise. Kelvin output noise is then investigated by modeling the surrounding bias feedback loop. A design rule is proposed that allows choosing the AC modulation frequency for optimized sharing of the PLL bandwidth between Kelvin and topography loops. A crossover criterion determines as a function of bandwidth, temperature and probe parameters whether thermal or detector noise is the dominating noise source. Probe merit factors for both cases are then established, suggesting how to tackle noise performance by probe design. Typical merit factors of common probe types are compared. This comprehensive study is an encouraging step toward a more integral performance assessment and a remedy against focusing on single aspects and optimizing around randomly chosen key values.

Analysis and Design of Low-Jitter Digital Bang-Bang Phase-Locked Loops

Digital phase-locked loops based on bang-bang phase detectors are attractive candidates for low-jitter clock-frequency multiplication. Unfortunately, the coarse quantization of phase error makes these systems prone to the generation of limit cycles appearing as unwanted spurs in the spectrum. The random noise contributed by building blocks and acting as dithering signal can eliminate those spurs. The quantitative analysis of those phenomena becomes more involved when a DCO with relaxed intrinsic resolution, such as a ΔΣ-DCO is employed, and when practical spectra of random noise sources are considered. In this work, the expression of jitter is calculated in closed-form taking into account the quantization, introduced by both phase detector and DCO, and the phase noise of DCO, with both 1/f 2 and 1/f 3 components. Combining these results, a closed-form expression of the total output jitter as a function of loop parameters and noise sources is developed which suggests a minimum-jitter design strategy. The proposed analysis and optimization are validated both numerically and experimentally on a 320-MHz digital bang-bang PLL fabricated in a 65-nm CMOS process.

On the mechanism of nondestructive evaluation of cementite content in steels using a combination of magnetic Barkhausen noise and magnetic force microscopy techniques

The influence of carbon content in the form of globular cementite precipitates in unalloyed steels was macroscopically characterized by means of magnetic hysteresis loop and Barkhausen noise techniques. The choice of the frequency of the applied field has a strong influence on the Barkhausen noise profiles. At sufficiently high frequency (0.5Hz) there are two peaks, one at lower field, the amplitude of which corresponds to the amount of ferrite and one at higher field, the amplitude of which corresponds to the amount of the cementite phase, respectively. Magnetic force microscopy and electron backscattered diffraction techniques were used to determine the magnetic and crystallographic microstructures of the steels. Cementite has its own domain structure and stray fields which influence the magnetization process of the steel by its own magnetic contribution. When an external magnetic field is applied, the magnetization process in ferrite occurs mainly at lower fields through the 180° and 90° domain walls. A higher field is required for the observation of 180° domain wall movements in cementite.

Magnetic micro- and nanostructures of unalloyed steels: Domain wall interactions with cementite precipitates observed by MFM

The morphology and content of a cementite phase controls the macroscopic, mechanical and magnetic properties of steels. The influence of the cementite content on the bulk magnetic properties in unalloyed steels was observed in hysteresis loop and Barkhausen noise signals. Globular cementite embedded in a ferrite matrix is characterized by atomic force microscopy and magnetic force microscopy. Size, shape and orientation of the grains influence the domain configuration. When an external magnetic field is applied, the magnetization process occurs mainly in the ferrite matrix. The Bloch walls in the ferrite matrix move, and they are pinned by the cementite precipitates. This microscopic observation correlates with the macroscopic magnetic properties of the investigated material.

Rayleigh-Scattering-Induced RIN and Amplitude-to-Phase Conversion as a Source of Length-Dependent Phase Noise in OEOs

Optoelectronic oscillators (OEOs) are hybrid RF-photonic oscillators that promise to be environmentally robust frequency sources with very low phase noise. Recent experiments have shown that the excess flicker phase noise in these systems grows with the length of the optical fiber loop. In this paper, we detail a mechanism for this length-dependent flicker noise in which Rayleigh-scattering-induced amplitude noise in the optical fiber combines with amplitude-to-phase noise conversion in the nonlinear electronic components. We derive an analytic model of the loop noise that includes these effects and verify this model by comparing it to numerical calculations and experimental results.

A Chip Scale Atomic Clock Driven Receiver for Multi-Constellation GNSS

This paper presents the design and implementation of a Chip Scale Atomic Clock (CSAC) driven dual-channel Digitally Configurable Receiver (DCR) for Global Navigation Satellite Systems (GNSS). The receiver is intended to be used for research applications such as; multipath mitigation, scintillation assessment, advanced satellite clock and spatial frame transformation modelling, Precise Point Positioning (PPP) as well as rapid development and assessment of novel circuits and systems for GNSS receivers. A novel sub-Nyquist sampling (subsampling) receiver architecture incorporating dual-band microstrip RF filters is employed in order to minimize the complexity of the multi-frequency Radio Frequency (RF) front-end. Moreover, the digital receiver incorporates a novel and complexity-reduced Fast Fourier Transform (FFT) core for signal acquisition as well as COordinate Rotation DIgital Computer (CORDIC) cores for the code/carrier discriminators in order to minimize the resource allocation on the FPGA. The receiver also provides easy access to enable adjustment of its internal parameters such as; RF gain, position update rate, tracking channel correlator spacing and code/carrier loop noise bandwidth. Correlator outputs, code/carrier error, Carrier-to-Noise Ratio (C/N0), navigation and RINEX data are provided to the end-user in real-time. This paper collectively highlights and reports on the implementation, test and validation of the novel techniques, elements and approaches in both the RF and digital part of the DCR that comprise the multi-constellation receiver.

Performance Prediction of a Synchronization Link for Distributed Aerospace Wireless Systems

For reasons of stealth and other operational advantages, distributed aerospace wireless systems have received much attention in recent years. In a distributed aerospace wireless system, since the transmitter and receiver placed on separated platforms which use independent master oscillators, there is no cancellation of low-frequency phase noise as in the monostatic cases. Thus, high accurate time and frequency synchronization techniques are required for distributed wireless systems. The use of a dedicated synchronization link to quantify and compensate oscillator frequency instability is investigated in this paper. With the mathematical statistical models of phase noise, closed-form analytic expressions for the synchronization link performance are derived. The possible error contributions including oscillator, phase-locked loop, and receiver noise are quantified. The link synchronization performance is predicted by utilizing the knowledge of the statistical models, system error contributions, and sampling considerations. Simulation results show that effective synchronization error compensation can be achieved by using this dedicated synchronization link.

Identification of Artificial Neural Network Models for Three-Dimensional Simulation of a Vibration-Acoustic Dynamic System

Industrial noise can be successfully mitigated with the combined use of passive and Active Noise Control (ANC) strategies. In a noisy area, a practical solution for noise attenuation may include both the use of baffles and ANC. When the operator is required to stay in movement in a delimited spatial area, conventional ANC is usually not able to adequately cancel the noise over the whole area. New control strategies need to be devised to achieve acceptable spatial coverage. A three-dimensional actuator model is proposed in this paper. Active Noise Control (ANC) usually requires a feedback noise measurement for the proper response of the loop controller. In some situations, especially where the real-time tridimensional positioning of a feedback transducer is unfeasible, the availability of a 3D precise noise level estimator is indispensable. In our previous works [1,2], using a vibrating signal of the primary source of noise as an input reference for spatial noise level prediction proved to be a very good choice. Another interesting aspect observed in those previous works was the need for a variable-structure linear model, which is equivalent to a sort of a nonlinear model, with unknown analytical equivalence until now. To overcome this in this paper we propose a model structure based on an Artificial Neural Network (ANN) as a nonlinear black-box model to capture the dynamic nonlinear behaveior of the investigated process. This can be used in a future closed loop noise cancelling strategy. We devise an ANN architecture and a corresponding training methodology to cope with the problem, and a MISO (Multi-Input Single-Output) model structure is used in the identification of the system dynamics. A metric is established to compare the obtained results with other works elsewhere. The results show that the obtained model is consistent and it adequately describes the main dynamics of the studied phenomenon, showing that the MISO approach using an ANN is appropriate for the simulation of the investigated process. A clear conclusion is reached highlighting the promising results obtained using this kind of modeling for ANC.

All-Digital Radio-Frequency Signal Distribution Via Optical Fibers

We present a radio-frequency (RF) signal distribution system via optical fibers. We utilize an all-digital platform that encompasses a phase-locked loop, numerically-controlled oscillator, and fiber phase noise cancellation system. Our system achieves a fractional frequency transfer stability of 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> at 1 s and 6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-17</sup> at one day for the distribution of RF signals over 70 km of optical fiber. We demonstrate that this performance can be achieved with standard crystal oscillators. Our system is scalable, configurable, and flexible, allowing distribution of signals at different frequencies while maintaining over two orders of magnitude of the fiber phase noise suppression.

ON THE DESIGN OF ADAPTIVE-BANDWIDTH ALL-DIGITAL PHASE-LOCKED LOOPS

The second-order adaptive-bandwidth all-digital phase-locked loop (ADB-ADPLL) is designed and analyzed by using a new design procedure. Based on a discrete-time analogy of a continuous-time PLL (CTPLL) with the z-transform, the design criterion of the ADB-ADPLL is derived and a design procedure is developed. Following the design criterion, the ADB-ADPLL can adapt its system parameters to balance the loop noise bandwidth and lock-in time. According to the design criterion, the ratio of the loop bandwidth to the reference input frequency can be maintained as a constant if the sampling frequency is a fixed multiplier of the input frequency. An example is given to illustrate the design procedure and simulation results are presented to validate the adaptive characteristics with respect to the phase noise and varying bands of input frequency.

Radiation tolerance of a spin-dependent tunnelling magnetometer for space applications

To meet the increasing demand for miniaturized space instruments, efforts have been made to miniaturize traditional magnetometers, e.g. fluxgate and spin-exchange relaxation-free magnetometers. These have, for different reasons, turned out to be difficult. New technologies are needed, and promising in this respect are tunnelling magnetoresistive (TMR) magnetometers, which are based on thin film technology. However, all new space devices first have to be qualified, particularly in terms of radiation resistance. A study on TMR magnetometers' vulnerability to radiation is crucial, considering the fact that they employ a dielectric barrier, which can be susceptible to charge trapping from ionizing radiation. Here, a TMR-based magnetometer, called the spin-dependent tunnelling magnetometer (SDTM), is presented. A magnetometer chip consisting of three Wheatstone bridges, with an angular pitch of 120°, was fabricated using microstructure technology. Each branch of the Wheatstone bridges consists of eight pairs of magnetic tunnel junctions (MTJs) connected in series. Two such chips are used to measure the three-dimensional magnetic field vector. To investigate the SDTM's resistance to radiation, one branch of a Wheatstone bridge was irradiated with gamma rays from a Co60 source with a dose rate of 10.9 rad min−1 to a total dose of 100 krad. The TMR of the branch was monitored in situ, and the easy axis TMR loop and low-frequency noise characteristics of a single MTJ were acquired before and after irradiation with the total dose. It was concluded that radiation did not influence the MTJs in any noticeable way in terms of the TMR ratio, coercivity, magnetostatic coupling or low-frequency noise.

Shot-noise-limited control-loop noise in an interferometer with multiple degrees of freedom

Precise measurements, such as those made with interferometric gravitational-wave detectors, require the measurement device to be properly controlled so that the sensitivity can be as high as possible. Mirrors in the interferometer are to be located at specific operation points to isolate laser noise and to accumulate the signal in resonant cavities. On the other hand, rigid control of an auxiliary degree of freedom may result in imposing sensing noise of the control on the target object as excess force noise. Evaluation of this so-called loop noise is important in order to design a decent control scheme of the measurement device. In this paper, we show the method to calculate the level of loop noise, which has been recently implemented in simulation tools that are broadly used for designing gravitational-wave detectors.

Verification of time-delay interferometry techniques using the University of Florida LISA interferometry simulator

Laser Interferometer Space Antenna (LISA) is a cooperative NASA/ESA mission proposed to directly measure gravitational waves (GW) in the frequency range from to with an optimal strain sensitivity of at . LISA will utilize a modified Michelson interferometer to measure length changes of between drag-free proof masses located on three separate spacecraft (SC) separated by a distance of . The University of Florida has developed a hardware-in-the-loop simulator of the LISA constellation to verify the laser noise cancellation technique known as time-delay interferometry (TDI). We replicate the frequency stabilization of the laser on the local SC and the phase-locking of the lasers on the far SC. The laser photodetector beatnotes are electronically delayed, Doppler shifted and applied with a mock GW signal to simulate the laser link between the SC. The beatnotes are also measured with a LISA-like phasemeter and the data are used to extract the laser phase and residual phase-lock loop noise in post-processing through TDI. This uncovers the GW modulation signal buried under the laser noise. The results are then compared to the requirements defined by the LISA science collaboration.

A Completely Configurable Digital System for Simultaneous Measurements of Hysteresis Loops and Barkhausen Noise

This paper describes a new accurate completely digital configurable computer-aided system for the simultaneous measurements of magnetic hysteresis loops and Barkhausen noise in a wide range of excitation frequencies (from 0.01 to 80 Hz) for the purposes of inspection of material properties and microstructure characterization. The importance of the correct choice of the data-acquisition (DAQ) card to have enough resolution in both hysteresis loop and magnetic Barkhausen noise (MBN) measurements is emphasized. Both the magnetic induction signal to construct the magnetic hysteresis loop and the Barkhausen noise are computed by the digital processing (numerical integration and digital filtering, respectively) of the induced electromotive force (EMF) signal. The accuracy of the hysteresis loop measurements is improved by using additional digital filters. The resolution of MBN results in simultaneous measurements is tested. Finally, some results of hysteresis loops and root-mean-square (RMS) envelopes of the MBN signal are presented to show the capability of the system to work at different excitation frequencies without changing any hardware.

Noise figure limits for circular loop MR coils

Circular loops are the most common MR detectors. Loop arrays offer improved signal-to-noise ratios (SNRs) and spatial resolution, and enable parallel imaging. As loop size decreases, loop noise increases relative to sample noise, ultimately dominating the SNR. Here, relative noise contributions from the sample and the coil are quantified by a coil noise figure (NF), NF(coil), which adds to the conventional system NF. NF(coil) is determined from the ratio of unloaded-to-loaded coil quality factors Q. Losses from conductors, capacitors, solder joints, eddy currents in overlapped array coils, and the sample are measured and/or computed from 40 to 400 MHz using analytical and full-wave numerical electromagnetic analysis. The Qs are measured for round wire and tape loops tuned from 50 to 400 MHz. NF(coil) is determined as a function of the radius, frequency, and number of tuning capacitors. The computed and experimental Qs and NF(coil)s agree within approximately 10%. The NF(coil) values for 3 cm-diameter wire coils are 3 dB, 1.9 dB, 0.8 dB, 0.2 dB, and 0.1 dB, at 1T, 1.5T, 3T, 7T, and 9.4T, respectively. Wire and tape perform similarly, but tape coils in arrays have substantial eddy current losses. The ability to characterize and reliably predict component- and geometry-associated coil losses is key to designing SNR-optimized loop and phased-array detectors.

Fault diagnosis for magnetic bearing systems

A full fault diagnosis for active magnetic bearing (AMB) and rotor systems to monitor the closed-loop operation and analyze fault patterns on-line in case any malfunction occurs is proposed in this paper. Most traditional approaches for fault diagnosis are based on actuator or sensor diagnosis individually and can solely detect a single fault at a time. This research combines two diagnosis methodologies by using both state estimators and parameter estimators to detect, identify and analyze actuators and sensors faults in AMB/rotor systems. The proposed fault diagnosis algorithm not only enhances the diagnosis accuracy, but also illustrates the capability to detect multiple sensors faults which occur concurrently. The efficacy of the presented algorithm has been verified by computer simulations and intensive experiments. The test rig for experiments is equipped with AMB, interface module (dSPACE DS1104), data acquisition unit MATLAB/Simulink simulation environment. At last, the fault patterns, such as bias, multiplicative loop gain variation and noise addition, can be identified by the algorithm presented in this work. In other words, the proposed diagnosis algorithm is able to detect faults at the first moment, find which sensors or actuators under failure and identify which fault pattern the found faults belong to.

Experimental Analysis of Substrate Noise Effect on PLL Performance

This paper describes experimental approaches to analyze the effect of the substrate noise on phase-locked loop (PLL) performance. Spectral analysis considering noise transfer functions of the PLL is used to identify the substrate-noise sensitive components of the PLL. Analyzing the sidebands seen in a spectrum analyzer confirms the importance of knowing the PLL loop dynamics and noise transfer functions. It also leads to the conclusion that the PLL blocks other than the VCO can be more sensitive to substrate noise coupling, depending on the substrate noise frequency. Furthermore, the result shows that intermodulation near the reference clock frequency could be a dominant source of generating sidebands in fractional-N PLLs.

CMOS implementation of a 1.6 GHz low voltage low phase noise quadrature output frequency synthesizer with automatic amplitude control

This article presents the design of a 1.2 V CMOS low phase noise quadrature output frequency synthesizer (FS) to be used for a GPS tuner application. Special reference is made to the design of a wide tuning range quadrature output voltage-controlled oscillator which is equipped with an automatic amplitude controller. It exhibits a phase noise response of less than ?115 dBc/Hz at an offset of 1 MHz from the carrier and has a tuning range of over 36%. The effect of the automatic amplitude control is shown to improve phase noise at high oscillation frequencies and its noise has a negligible effect on the phase noise response even at low offset frequencies from the carrier. Preliminary analysis is presented showing the negligible effect of a DC---DC converter on the spurious level of the FS, included to permit the use of low sensitivity varactors. Design guidelines for reducing both the loop noise and the AM-to-PM conversion factors of the oscillator are also given. The design was made using the STMicroelectronics 0.13 μm HCMOS9-RF technology design kit.