Frequency Dithering Research Articles

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Gyroscope`s deadzone is a region where can not detect the rate even though the actual rotation is applied. This paper analyzed the cause of deadzone by modeling/simulation and introduced pulse dithering method to overcome. From the testing of 3-axis fiber optic gyro system using 900m fiber, it confirmed deadzone could be effectively eliminated by combination of three factors, dither amplitude, dither frequency, and gyro loop gain.

A novel way for wavelength locking with acousto-optic frequency modulation

A novel wavelength locking scheme called acousto-optic frequency modulation (AOFM) is put forward and demonstrated experimentally. The laser frequency is modulated by an acousto-optic modulator, rather than direct dithering on the laser resonator. A new optical configuration is proposed to compensate the angular deflection of the acousto-optic modulator, which is driven by a Direct Digital Synthesis generator with a frequency stability and precision on the order of Hz. This locking scheme is relatively simple and economical, and it can avoid extra frequency and intensity noise due to the direct frequency dither on the laser resonator in the conventional saturation absorption locking scheme. Our scheme provides a new way to improve the noise and stability of the tunable laser.

Quantitative Study of Optical Frequency Noise to Intensity Noise Conversion in Line-by-Line Pulse Shaping

We report the first quantitative study of intensity noise induced in line-by-line pulse shaping in response to time-varying changes in the comb frequency offset. Controllable comb linewidth broadening is synthesized through frequency dithering of a continuous-wave laser that is fed to a phase modulator. An electrical spectrum analyzer is used to examine the current power spectra of shaped time-domain intensity waveforms subject to comb frequency noise. A theoretical model predicting a 20 dB/decade scaling relation between the dither-induced noise and the frequency dither amplitude is presented. A numerical simulation method capable of predicting the precise form of the RF power spectrum in the presence of optical frequency dithering is explained. Two line-by-line shaping cases are considered in detail. Experimental data are in excellent agreement with the simulated results down to frequency dithers of a few tenths of a percent of the comb spacing. Tolerances to laser frequency fluctuations are given for several simple pulse shaping examples. The effect of pulse shaper parameters is also discussed.

Reduction of EMI in AC Drives Through Dithering Within Limited Switching Frequency Range

In this paper, a method is presented to reduce electromagnetic (EM) emissions in AC drives. This method is applicable to many AC drives. It is proposed to dither the switching frequency of the power devices of an inverter in a pseudorandom way to spread out the emitted RF energy over a larger frequency range. The proposed method requires only software changes. Practical constraints to implement the frequency dithering approach are discussed. Simulation and measurement results show an improvement of more than 10 dB. The proposed method also converts specific spikes in the long-wave range from narrowband to broadband noise, which results in less stringent EM emission requirements for many applications.

Tri-state Modulation Power Driving of Electro-hydraulic Proportional Amplifier

Switch electro-hydraulic proportional amplifier(PA) widely employs single switch modulation power driving(SSMPD) or reverse discharging power driving(RDPD) at present.SSMPD has slow dynamic response,and can't adjust independently the dither signal's amplitude and frequency;RDPD accelerates the current decay;consequently,it increases current ripple and power loss.For the purpose of solving the above mentioned problem,the tri-state modulation power driving(TSMPD) scheme was proposed for improving the performance of power driving.Detailedly,the hardware circuit for the tri-state modulation power driving is designed;the tri-state modulation algorithm is realized by digital signal processor(DSP).The tri-state modulation power driving is investigated by experiments,comparetive experiments among the single switch modulation power driving(SSMPD),reverse discharging power driving(RDPD),and the TSMPD are implemented,and the experimental results demonstrate that the linearity error of TSMDP meets the requirement of PA;the current response of TSMSP is the best;the amplitude of ripple current of the TSMPD can be reduced without increasing frequency of PWM,in addition,dither signal amplitude and frequency can be adjusted independently for each other.It is very meaningful to guide the development of high performance proportional amplifier for high frequency response proportional solenoid.

Improved direct torque control of induction motor with dither injection

In this paper, a three-level inverter-fed induction motor drive operating under Direct Torque Control (DTC) is presented. A triangular wave is used as dither signal of minute amplitude (for torque hysteresis band and flux hysteresis band respectively) in the error block. This method minimizes flux and torque ripple in a three-level inverter fed induction motor drive while the dynamic performance is not affected. The optimal value of dither frequency and magnitude is found out under free running condition. The proposed technique reduces torque ripple by 60% (peak to peak) compared to the case without dither injection, results in low acoustic noise and increases the switching frequency of the inverter. A laboratory prototype of the drive system has been developed and the simulation and experimental results are reported.

Tunable Diode Laser Spectroscopy for Industrial Process Applications: System Characterization in Conventional and New Approaches

Tunable diode laser spectroscopy (TDLS) can only be successfully implemented if a number of system characterization procedures and critical parameter measurements can be made accurately. These include: application of a wavelength/frequency scale to the signals recovered in time; measurement of the frequency dither applied to the laser; measurement of the relative phase between the laser power modulation and frequency modulation; determination of the background amplitude modulation for normalization purposes and measurement of required cross broadening coefficients for the host/target gas mixtures. Easy to implement, accurate and low-cost systems and procedures for achieving these are described and validated below. They were developed for two new approaches to TDLS measurements, viz the residual amplitude modulation (RAM) technique and the phasor decomposition (PD) method, but are equally applicable to all forms of TDLS. Following full system characterization using the new techniques, measurements of the absolute transmission function of the 1650.96 nm absorption line of methane over a wide range of concentration and pressure were made using the RAM technique. The close agreement with theoretical traces derived from HITRAN data validated the entire approach taken, including the system characterization procedures. In addition, measurements of a wide range of gas concentration and pressure were made by curve fitting theoretical traces to the measured transmission functions obtained using a variety of operating conditions. Again, the low errors confirmed the validity of the new methods and the system characterization/measurement procedures described here.

Dependence of the Error in the Optimal Solution of Perturbation‐Based Extremum Seeking Methods on the Excitation Frequency

AbstractIn perturbation‐based extremum‐seeking methods, an excitation signal is added to the input, and the gradient, computed from the correlation between the input and output variations, is forced to zero. The main drawback of the method is that the speed of convergence, which is linked to the dither frequency, is slow due to the low value of dither frequency typically chosen. Increasing the excitation frequency may cause instability, but that could be corrected by phase compensation. In this paper, it is shown that an additional problem exists, i.e., the distance between the optimum and solution reached by the perturbation method is proportional to the square of the frequency of excitation and does not go to zero even when the amplitude of the excitation goes to zero. However, for Wiener/Hammerstein approximations, the error will indeed go to zero with the excitation amplitude. Simulation results on a distributed reaction system are used to illustrate the concepts presented in this work.

A material rigidity effect of a bimorph piezoelectric actuator

This paper presents the numerical modeling of a piezoelectric actuator used to avoid thelimitation of the lock-in region in a ring resonator. Ring resonators have proved suitable foruse as inertial sensors for navigation, guidance and attitude controls. However, theiraccuracy has been limited by the lock-in region due to frequency coupling between twocounter-propagating waves at low rotation rates. This coupling introduces no phasedifference, and no angular increment is detected. The problem can be overcome bymechanically dithering the ring resonator. Mechanically, the vibro-elastic bimorphpiezoelectric actuator has been used as a control but is influenced by piezoelectric rigidityeffects. To more accurately predict the dithering frequency of a mechanical dither,numerical modeling of a piezoelectric actuator includes the piezoelectric rigidity effect ofthe actuator, which occurs in both the static and dynamic behaviors of composite plateshaving piezoelectric layers symmetrically bonded to the top and bottom surfaces.Corrections were made to figures 1 and 2 on 13 June 2007. The corrected electronic version is identical to the print version

Rayleigh Scattering Reduction by Means of Optical Frequency Dithering in Passive Optical Networks With Remotely Seeded ONUs

With the purpose of reducing the crosstalk caused by Rayleigh scattering in bidirectional centralized light systems, we propose and experimentally demonstrate an optical frequency modulation to broaden the optical spectrum effectively. Analytic expressions for the Q-parameter of the signal affected by Rayleigh backscattering are also given and experimentally checked, both for optical frequency stable and dithered sources

Analysis of frequency offset in the frequency stabilization of semiconductor laser based on frequency dithering technique

We investigate the frequency offset in the frequency stabilization of a semiconductor laser based on a frequency-dithering technique. An analytical model is presented to describe the effects of the amplitude modulation and the phase delay between the amplitude and frequency modulation on the frequency stabilization. We also experimentally and analytically show that the frequency offset could be reduced by using an appropriate phase-sensitive detection.

Effect of burst-modulated sinusoidal dither waveforms on the effectiveness of dither forces to eliminate friction-induced oscillations

This paper examines the effectiveness of high-frequency dither-cancellation techniques using burst-modulated signals. The classic single-degree-of-freedom (SDOF), mass on moving belt, model is analyzed using the method of averaging and numerical integration of system dynamics. Two different friction laws are used to model the contact point, both exhibiting a negative friction coefficient-velocity relationship. Recent results [M. Michaux and A. Ferri, Proceedings of IDETC05 Paper no. DETC2005-84491 (2005)] found that sinusoidal dither forces could stabilize or destabilize such a system, depending on the system and frictional characteristics as well as the dither signal amplitude and frequency. This paper extends this previous analysis to burst-modulated sinusoidal dither signals. Earlier experimental research has shown burst-modulated dither signals to be an effective method of suppressing automotive brake squeal. It is found that, for a given amplitude and frequency, burst signals are also capable of stabilizing the system. Individual effects of each burst parameter on system stability are established.

Braking Impact of Normal Dither Signals

Dither control is a method of introducing high-frequency control efforts into a system to suppress a lower-frequency disturbance. One application of dither control is the suppression of automotive brake squeal. Brake squeal is a problem that has plagued the automotive industry for years. Placing a piezoceramic stack actuator in the piston of a floating caliper brake creates an experimental normal dither system. Many theoretical models indicate a reduction in the braking torque due to the normal dither signal. Using a Hertzian contact stiffness model, the loss in friction is due to lowering the average normal force. There are also theories that the dither signal eliminates the “stick-slip” oscillation causing an effective decrease in the friction force. Yet another theory indicates that the effective contact area is reduced, lowering the mean coefficient of friction. A particular approach considering a single-degree-of-freedom friction oscillator predicts a maximum friction reduction of 10%, occurring at the primary resonance of the system. This paper will concentrate on validating this claim by experimentally determining braking torque reduction for a variety of dither control signals. Several dither control frequencies were chosen at system resonances, while others were chosen at frequencies most likely to provide control of the system. These frequencies were chosen based on previous squeal suppression research. The results indicate that dither control frequencies at system resonances have a greater impact on the braking system’s performance. In general, dither control reduces braking torque by no more than 2%.

Characterization of thin real-time holographic media by dithered four-wave mixing

Photosensitive optical media of the types that are used in real-time holography generally exhibit both photorefractive and photochromic response. The parameters that characterize each of these types of response can be extracted by detailed quantitative analysis of four-wave mixing experiments in the Raman–Nath regime. This principle has been tested using reactive eyeglass lenses. The techniques of Fourier optics have been applied to the analysis of diffraction from amplitude/phase gratings produced in the photochromic glass by laser illumination. Dithering of a laser-induced fringe pattern produces a combination of two-wave and four-wave mixing that can be analysed in terms of amplitudes proportional to products of Bessel functions of different orders. The incident and diffracted beams are predicted, and observed, to be modulated at the dither frequency and its harmonics. The small dither amplitudes that were employed, made possible by use of a phase-sensitive detection technique, allowed Bessel function expansions to be truncated after only a few terms for the purpose of parameter estimation. The technique has allowed the very small refractive index change associated with dispersion of the photo-induced absorption in silver halide doped photochromic glass to be measured for the first time.

SUBTLETIES IN THE AVERAGING OF HYBRID SYSTEMS WITH APPLICATIONS TO POWER ELECTRONICS

Dither signals are commonly used in electronics for implementing different type of modulations in power converters, which represent a very interesting class of hybrid systems. It was recently shown that a nonsmooth dithered system can be approximated by an averaged system provided that the dither frequency is sufficiently high and that the amplitude distribution function of the dither is absolutely continuous and has bounded derivative. This result is exploited in this paper for power converters. Averaged models corresponding to various shapes of dither signal are analyzed, showing that dither with Lipschitz continuous amplitude distribution function can be used to adapt the equivalent gain of the power converter.

Single Stage Self-Oscillating HPF Electronic Ballast

This paper presents a single stage self-oscillating high power factor (HPF) electronic ballast more suitable for both low power levels (because it operates in discontinuous conduction mode) and low AC mains applications (since it employs an input doubler rectifier). The electronic ballast is based on a high frequency dither signal, which shapes the input current in a sinusoidal waveform. In order to reduce the electronic ballast components the self-oscillation technique has been employed. An electronic ballast prototype operating at 25 kHz has been implemented to drive two 40 W straight-type fluorescent lamps from a 127 V utility line. High power factor is achieved even though the electronic ballast drives just one fluorescent lamp. The experimental results demonstrated the electronic ballast operation.

Stochastic resonance behaviors of bistable systems connected in series

The stochastic resonance(SR) characteristics of two bistable systems connected in series have been investigated. It is deduced that the first bistable system of the cascaded system is most important because of its converting a white noise into a color one, and the subsequent bistable systems continuously concentrate noise energy into lowfrequency area in terms of Lorentzian distribution, which weakens the highfrequency dithering of the last output waveform and outlines the basic shape of the wave. The law of the signal spectral amplitude varying with noise intensity indicates that within a limited lowfrequency band, the cascaded system is able to promote the height of the signal spectral spike by a certain amount of noise. If the former of the cascaded system does not stay in SR, the latter could not optimize the former output to become a SR state. With the increase of the number of the bistable systems in the cascaded system, the lowfrequency area where most of the noise energy is collected will be narrowed gradually, and hence the signal peak is easily reduced and submerged in noise. For this case, in spite of using the twice-sampling technique to improve the signal spectral spike, the improvement is limited. Therefore, a single bistable system is effective for signal detection.

Modulation-Free Frequency Stabilization of a Grating-External-Cavity Diode Laser by Magnetically Induced sub-Doppler Dichroism in Cesium Vapor Cell

Thanks to the Zeeman effect and the saturation absorption spectroscopic technique, magnetically induced sub-Doppler dichroism has been experimentally demonstrated in a cesium vapor cell. A dispersion-like frequency-discriminating signal is obtained by this sub-Doppler dichroism. The phase-sensitive detection via lock-in is no longer required because there is no frequency dither on the laser. A grating-external-cavity 852 nm diode laser is frequency-stabilized to cesium 6 2S1/2 F = 4–6 2P3/2 F' = 4, 5 crossover by this modulation-free locking scheme. Compared with a frequency fluctuation of approximately 12 MHz under free-running conditions, a typical frequency jitter of less than +/- 260 kHz in 50 s was estimated in the preliminary stabilization. This locking scheme is relatively simple, and it can avoid extra noise due to the direct frequency dither on the laser source in the conventional saturation absorption locking technique.

A/D converters nonlinearity measurement and correction by frequency analysis and dither

In this paper, a new frequency-domain approach to measure and correct the static nonlinearity error of analog-to-digital converters is analyzed. The nonlinearity is measured as a linear combination of the Chebyshev polynomials, whose coefficients are derived via frequency-domain analysis, and corrected with a nonlinear equation solving method, which makes use of the parametric form of the static characteristics. The proposed methodology is especially suited for dithered converters, due to their particular features of smoother nonlinearity and very high resolution. Both simulation and experimental results are reported, quantifying also the achieved increase of effective bits.

Optimizing the frequency in dithered laser gyroscopes

The dither frequency in a null-biased laser gyroscope is explored both analytically and experimentally. The agreement between theory and experiment is excellent and an optimum range for the dither frequency is derived.