Showing papers on "Frequency drift published in 2008"

Switching voltage regulator employing dynamic voltage scaling with hysteretic comparator

Abstract: A switching voltage regulator is disclosed operable to regulate a voltage supplied to system circuitry. A comparator compares an oscillator signal generated by a ring oscillator to a reference signal generated by a frequency generator. Switching circuitry charges a charging element in response to the comparison, and control circuitry adjusts a number of delay elements in the ring oscillator and a divider value of the frequency generator to generate hysteresis in the comparison. In one embodiment, the charging element is charged while a frequency of the reference signal is above a frequency of the oscillator signal.

Evolution of the quasi-periodic oscillation frequency in GRO J1655-40 - Implications for accretion disk dynamics

Abstract: Context. Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought to be due to oscillations of Comptonizing regions or hot blobs embedded in Keplerian disks. Any movement of these perturbations is expected systematically to change the QPO frequency.Aims. Our goal is to find systems where such a systematic drifts have been observed. We also try to find the real cause of such drifts and whether they shed some light on the accretion disk dynamics.Methods. Using archival data of the recent outburst of GRO J1655-40, we report the presence of such systematic drifts not only during the rising phase from the 25th of February 2005 to the 12th March 2005, when the QPO frequency monotonically increased from 82 mHz to 17.78 Hz but also in the decline phase from the 15th September 2005 to the 5th of October 2005, when the QPO frequency decreased from 13.14 Hz to 34 mHz.Results. We fitted the frequency drifts with the propagatory oscillating shock solution. In the shock-oscillation solution, the frequency is inversely proportional to the infall time scale from the shock location. We obtained the shock location and strength through such a fit. Conclusions. The astonishing smoothness of the variation of the QPO frequency over a period of weeks directly supports the view that it may due to the drift of an oscillating shock rather than the movements of a blob inside a differentially rotating disk.

Comparison of Different Frequency Controllers for a VSC-HVDC Supplied System

Abstract: This paper studies three different frequency controllers and their effects on the voltage disturbance ride-through capability of a VSC-HVDC supplied industrial system. The idea of implementing frequency controller is to improve the power quality of industrial plants by slightly decreasing the VSC output voltage frequency since industrial processes are more sensitive to voltage drops than frequency deviations. The first two controllers, frequency controllers I and II, are fixed frequency controllers and the third one, frequency controller III, is a PI frequency controller. In order to compare three different controllers, a system with a simplified VSC-HVDC and different load types is simulated in PSCAD/EMTDC. Simulation results show that with frequency controller III, the VSC-HVDC supplied industrial plant can avoid a voltage collapse by decreasing frequency during or after disturbances. Furthermore, with an increase of the converter current limit, the possibility of mitigating voltage dips increases. For frequency controllers I and II, the extent of the disturbance ride-through capability depends on the current limit of the VSC-HVDC. A higher current limit results in a higher ride-through capability. The effect of the dc capacitor on improving the system voltage disturbance tolerance is also investigated during and after disturbances when the VSC-HVDC uses frequency controller I. The system voltage disturbance ride-through capability increases with an increase of the dc capacitance or the current limit.

Power System Frequency Measurement Under Nonstationary Situations

Abstract: A new method for the measurement of the instantaneous power-system frequency is proposed. It is based on the frequency estimation of the voltage signal using three equidistant samples. An algorithm is developed that diminishes the variance of the estimation. The procedure is applied to the case of single- and three-phase networks, and uncertainty in the frequency estimation is obtained with simulated signal and severe conditions of signal quality. A frequency variation has been assumed as plusmn2 Hz around the nominal value, with a maximum rate of change of 1 Hz/s. The uncertainty of 25 mHz and 3.5 mHz has been obtained for single- and three-phase signals, respectively. A low-cost virtual instrument has been developed to make frequency measurements over the actual voltage signal.

A Temperature-Stable Film Bulk Acoustic Wave Oscillator

Abstract: This letter reports a passively temperature-compensated CMOS oscillator utilizing a film bulk acoustic resonator. The resonator exhibiting an f ldr Q product of 2-4 X 1012 s-1 is composed of molybdenum, aluminum nitride, and a compensation material that has a positive temperature coefficient of Young's modulus. The 604-MHz oscillator consumes 5.3 mW from a 3.3-V supply and achieves excellent phase noise performances of -102, -130, and -149 dBc/Hz at 1, 10, and 100 kHz carrier offsets, respectively. The oscillator's temperature-dependent frequency drift is less than 80 ppm over a temperature range of -35degC to +85degC.

Integrated Phase-Locking Scheme for SDFT-Based Harmonic Analysis of Periodic Signals

Abstract: The sliding discrete Fourier transform splits periodic signals into selected harmonic components, as on-line time functions. Ordinarily, the sampling frequency is equal to the product of the nominal signal frequency and the window width N. However, when the signal frequency drifts, to avoid the phase and magnitude errors, the sampling frequency can be adaptively adjusted using the phase-error itself. An integrated phase-locked loop scheme and its parameters like hold-in, pull-in ranges, lock time, steady-state

Exploiting manufacturing variations for compensating environment-induced clock drift in time synchronization

Abstract: Time synchronization is an essential service in distributed computing and control systems. It is used to enable tasks such as synchronized data sampling and accurate time-of-flight estimation, which can be used to locate nodes. The deviation in nodes' knowledge of time and inter-node resynchronization rate are affected by three sources of time stamping errors: network wireless communication delays, platform hardware and software delays, and environment-dependent frequency drift characteristics of the clock source. The focus of this work is on the last source of error, the clock source, which becomes a bottleneck when either required time accuracy or available energy budget and bandwidth (and thus feasible resynchronization rate) are too stringent. Traditionally, this has required the use of expensive clock sources (such as temperature compensation using precise sensors and calibration models) that are not cost-effective in low-end wireless sensor nodes. Since the frequency of a crystal is a product of manufacturing and environmental parameters, we describe an approach that exploits the subtle manufacturing variation between a pair of inexpensive oscillators placed in close proximity to algorithmically compensate for the drift produced by the environment. The algorithm effectively uses the oscillators themselves as a sensor that can detect changes in frequency caused by a variety of environmental factors. We analyze the performance of our approach using behavioral models of crystal oscillators in our algorithm simulation. Then we apply the algorithm to an actual temperature dataset collected at the James Wildlife Reserve in Riverside County, California, and test the algorithms on a waveform generator based testbed. The result of our experiments show that the technique can effectively improve the frequency stability of an inexpensive uncompensated crystal 5 times with the potential for even higher gains in future implementations.

Steady state frequency control of variable frequency switching regulators

Abstract: A steady state frequency control circuit for a variable frequency regulator including an open loop frequency control circuit, a frequency detector and a comparator circuit. The variable frequency regulator provides a clock signal indicating actual operating frequency and has a frequency control parameter for adjusting steady state operating frequency. The frequency detector receives the clock signal and provides a frequency sense signal which is compared with a steady state frequency reference signal to provide a frequency adjust signal. The frequency control parameter is adjusted by the frequency adjust signal to control steady state frequency. A method of controlling steady state frequency of a variable frequency regulator includes using open loop frequency control, determining the operating frequency and providing a frequency sense signal, comparing the frequency sense signal with frequency reference signal and providing a frequency adjust signal, and adjusting the frequency control parameter based on the frequency adjust signal.

Alfvén ship waves: high-m ULF pulsations in the magnetosphere generated by a moving plasma inhomogeneity

Abstract: The generation of a high-m Alfvwave by sub- storm injected energetic particles in the magnetosphere is studied. The wave is supposed to be emitted by an alternating current created by the drifting particle cloud or ring current inhomogeneity. It is shown that the wave appears in some azimuthal location simultaneously with the particle cloud ar- rival at the same spot. The value of the azimuthal wave number is determined as m !/!d , where ! is the eigen- frequency of the standing Alfv´ en wave and !d is the particle drift frequency. The wave propagates westward, in the di- rection of the proton drift. Under the reasonable assumption about the density of the energetic particles, the amplitude of the generated wave is close to the observed amplitudes of poloidal ULF pulsations.

Simulations of coronal type III solar radio bursts: 2. Dynamic spectrum for typical parameters

Abstract: [1] Predictions are presented for the dynamic spectrum of a coronal type III burst observed at Earth, using a newly developed simulation model and employing realistic electron release and coronal parameters. The spectrum is studied in detail in association with the dynamics of beam and waves in the source. The frequency drift rate, radio flux, brightness temperature, and temporal profile of the type III burst agree semiquantitatively with typical observations. The simulation model is thus viable. Because of strong free-free absorption and scattering-induced damping, the flux of fp emission is significantly lower than that of 2fp emission and is below the lower thresholds of typical radio instruments. Moreover, the fp emission terminates at frequencies higher than the minimum simulated, and the 2fp emission appears to terminate at higher coronal altitudes that are not simulated because of computational limitations. Further simulations indicate that F-H pairs may exist under favorable conditions (e.g., generally, lower levels and larger length scales of the density fluctuations).

Frequency stabilization of an ultraviolet laser to ions in a discharge

Abstract: We stabilize an ultraviolet diode laser system at 369.5 nm to the optical absorption signal from Yb+ ions in a hollow-cathode discharge lamp. The error signal for stabilization is obtained by Zeeman spectroscopy of the 3 GHz wide absorption feature. The frequency stability is independently measured by comparison to the fluorescence signal from a laser-cooled crystal of Y174b+ ions in a linear Paul trap. We measure a frequency fluctuation of 1.7 MHz over 1000 s and a frequency drift of 20 MHz over 7 days. Our method is suitable for use in quantum information processing experiments with trapped ion crystals.

Systems and methods for voltage controlled oscillator calibration

Abstract: Various systems, methods and apparatus for calibrating a clock generating circuit are discussed herein. As one example, a method for calibrating a voltage controlled oscillator is disclosed. The method includes fixing the control voltage of a fine tune capacitor in the voltage controlled oscillator at a predetermined level. A binary search is performed in a digital circuit for a value of a calibration word that is used to enable switched capacitors in a coarse tune capacitor bank in the voltage controlled oscillator. The calibration word is fixed at the value determined by the binary search, and the control voltage of the fine tune capacitor is released to enable adjustment of the control voltage by a feedback signal to the voltage controlled oscillator.

Optical fiber distributed temperature and stress sensing device

Abstract: The invention discloses a sensing device of optical fiber distribution type temperature and stress and mainly comprises a light source module (1), a frequency discriminator module (2), and a thermo tank module (3), which are all connected with one another by polarization-preserving fiber The invention is a direct detection method which is based on optical fiber Raman scattering used as a carrier wave of temperature information, brillouin scattering used as a carrier wave of stress, rayleigh scattering used for measuring relative frequency of a outgoing laser beam to a frequency discriminator and Fabry-Perot etalon used for discriminating frequency and distributing sensing temperature and stress The invention has the advantages of simple structure, fine stability, avoidance of outgoing power of the light source during coherent detection, outgoing frequency of the light source Instability of acoustic modulation or electro-optic modulation frequency is directly referred to measure errors and the direct detection technology of the frequency discrimination is not sensitive to frequency drift of the light source and fluctuation of signal intensity

Thermally stable oscillator at 2.5 GHz using temperature compensated BAW resonator and its integrated temperature sensor

Abstract: This paper presents a miniaturized 2.5GHz frequency source based on compensated BAW resonator with its integrated temperature molybdenum sensor assembled on the differential Colpitts oscillator. The presence of silicon dioxide layer having a positive temperature coefficient compared to other layers is used to reduce the resonator's drift. A demonstration oscillator achieves a frequency drift of 40 ppm over a temperature range from -35degC to +85degC. The oscillator's phase noise of -94dBc/Hz at 2 KHz offset from the carrier is reported.

Frequency aiding method and system for navigation satellite receiver with crystal oscillator frequency hysteresis

Abstract: A method and apparatus for estimating oscillator signal variation due to temperature and for providing an estimated frequency to a GPS receiver in order to assist the GPS receiver to acquire the signals quickly is disclosed. A temperature sensor is closely thermally coupled with the crystal oscillator in the GPS receiver and during GPS tracking mode, when the error in the oscillator signal is known with precision, outer bounds of TCXO frequency at given temperatures are maintained, which may correspond to rising and falling temperature conditions. During acquisition mode, an estimated frequency value is provided to the GPS receiver based on a determined average of these bounds. Optionally, an uncertainty factor associated with the frequency estimated may also be provided. The two bounds take into account the hysteresis effects of the oscillator signal drift due to temperature so that a more accurate initial frequency estimate can be provided to the GPS receiver, thus reducing its average time to first fix.

Apparatus and method for measurement of temperature using oscillators

Abstract: A temperature sensor includes: a first oscillator that generates a first frequency signal; a second oscillator that generates a second frequency signal; a multiplexer that selectively passes the first frequency signal and the second frequency signal; and a frequency-to-digital converter that converts a frequency difference between the first frequency signal and the second frequency signal into a digital code.

Detecting method suitable for optical fiber distributed temperature and stress sensing device

Abstract: The invention discloses a detection method suitable for a sensing device of optical fiber distribution type temperature and stress. The sensing device of the optical fiber distribution type temperature and stress mainly comprises a light source module (1), a frequency discriminator module (2), and a thermo tank module (3), which are all connected with one another by polarization-preserving fiber. The detection method of the invention is a direct detection method which is based on optical fiber Raman scattering used as a carrier wave of temperature information, brillouin scattering used as a carrier wave of stress, rayleigh scattering used for measuring the relative frequency of a outgoing laser beam to the frequency discriminator and Fabry-Perot etalon used for discriminating frequency and distributing sensing temperature and stress. The invention has the advantages of simple structure, fine stability, avoidance of outgoing power of the light source during coherent detection, and outgoing frequency of the light source. Instability of acoustic modulation or electro-optic modulation frequency is directly referred to measure errors and the direct detection technology of frequency discrimination is not sensitive to the frequency drift of the light source and the fluctuation of signal intensity.

Apparatus for synchronizing ofdm signal using open-loop frequency synchronization method and frequency offset estimation scheme using the apparatus

Abstract: There are provided an apparatus for synchronizing an OFDM signal using an open-loop frequency synchronization method, which can estimate and compensate for various types of frequency errors generated in a frequency modulation broadcasting/communication system to which the open-loop frequency synchronization method is applied, and a frequency offset estimation scheme using the apparatus. To this end, the apparatus for synchronizing an OFDM signal using the open-loop frequency synchronization method comprises a time offset estimator, a time offset compensator, a fractional frequency offset estimator, an integer frequency offset estimator, a frequency offset controller and a frequency offset compensator. Accordingly, in the OFDM demodulation broadcasting/communication system using the open-loop frequency synchronization method, a frequency offset, which is generated due to the carrier frequency difference between a transmitter and a receiver, a frequency shift generated due to the mobile environment of a receiver, the temperature characteristic of a local oscillator, and the like, can be estimated and compensated.

Device and method for fast transition from preamble synchronization to data demodulation in direct sequence spread spectrum (DSSS) communications

Abstract: A device for fast transition from preamble synchronization of a received baseband signal to demodulation of the received baseband signal may include a baseband chip tracking loop to generate an offset tracking value to track any initial chip phase offset and Doppler-caused baseband chip frequency drift associated with the received baseband signal. The device may also include a numerical controlled oscillator to correct any Doppler-caused phase rotation associated with the received signal. The device may additionally include a preamble synchronization unit to detect a preamble of the received baseband signal, and to measure a chip phase offset and a baseband Doppler frequency shift associated with the received baseband signal. The chip phase offset may be used to set an initial chip phase offset value of the chip tracking loop so that the chip tracking loop starts with approximately a zero pull-in error. The baseband Doppler frequency shift may be used to set initial frequency offset values in the chip tracking loop and the numerical controlled oscillator so that both start with substantially near-zero offset errors for substantially immediate demodulation of the received signal. The device may further include an output device to output the data demodulated from the received baseband signal.

Method and apparatus for compensating temperature changes in an oscillator-based frequency synthesizer

Abstract: Architectures for compensating the frequency drift of an oscillator based frequency synthesizer circuit due to the change of temperature are disclosed. By applying a digitally controlled frequency word which represents the frequency difference between an output signal of a crystal oscillator and a temperature-compensated signal obtained from the output of a frequency synthesizer, the generated frequency signal is controlled so as to be temperature compensated over a wide temperature range. In one embodiment, a frequency locked loop is provided to perform functions to compensate for possible drifts in the reference signal. The frequency locked loop receives a digital frequency corrected control word based on at least a first parameter and a second parameter, wherein the first parameter is a combination of a fixed frequency control word and an automatic frequency correction word, and the second parameter is derived from an external source.

Faint solar radio structures from decametric observations

Abstract: Aims. Decameter radio observations of the solar corona reveal the presence of numerous faint frequency drifting emissions, similar to “solar S bursts” which are reported in the literature. We present a statistical analysis of the characteristics of these emissions and propose a mechanism to excite the Langmuir waves thought to be at the origin of these emissions. Methods. The observations were performed between 1998 and 2002 with the Digital Spectro Polarimeter (DSP) receivers operated at the UTR-2 and Nancay decameter radio telescopes in the frequency range 15–30 MHz. Our theoretical explanation is based on Vlasov-Ampere simulations.Results. Based on the frequency drift rate, three populations of structures can be identified. The largest population presents an average negative frequency drift of -0.9 MHz s-1 and a lifetime up to 11 s (median value of 2.72 s). A second population shows a very small frequency drift of -0.1 MHz s-1 and a short lifetime of about 1 s. The third population presents an average positive frequency drift of +0.95 MHz s-1 and a lifetime of up to 3 s. Also, the frequency drift as a function of frequency is consistent with the former results, which present results in higher frequency range. No specific relationship was found between the occurrence of these emissions and the solar cycle or presence of flares. Assuming that these emissions are produced by “electron clouds” propagating the solar corona, we deduce electron velocities of about 3–5 times the electron thermal velocity. As previously shown, a localized, time-dependent modulation of the electron distribution function (heating) leads to low velocity electron clouds (consistent with observations), which, in turn, can generate Langmuir waves and electromagnetic signals by nonlinear processes.

Crystal oscillator temperature control and compensation

Abstract: Crystal oscillator control and calibration is disclosed. Temperature and frequency control circuits included on a printed circuit board (PCB) comprising a crystal oscillator are used to determine, for each of a plurality of set points in a range of sensed internal temperatures sensed by an internal temperature sensing circuit or device located adjacent to the oscillator in a thermally insulated region of the PCB, a corresponding compensation required to be applied to maintain a desired oscillator output frequency. The PCB is configured to use at least the determined compensation values and a sensed internal temperature to determine during operation of the PCB a compensation, if any, to be applied to maintain the desired oscillator output frequency.

Poly-phase frequency synthesis oscillator

Abstract: A frequency synthesis/multiplication circuit and method for multiplying the frequency of a reference signal. In one embodiment, multiple versions of the reference signal are generated having different phases relative to one another, and these multiple versions are combined to form an output signal having a frequency that is a multiple of the frequency of the reference signal.

An analysis of the autodyne effect of oscillators with linear frequency modulation

Abstract: General equations are obtained for the autodyne response in the case of an arbitrary frequency modulation both over the active element bias circuit and voltage variation on the voltage-dependent capacitor (varicap). The results of investigation of an autodyne oscillator with linear frequency modulation following the antisymmetric and symmetric saw-tooth function are presented, with the oscillator being affected by its own reflected radiation. Special features of self-oscillations of such autodynes are considered, with the aim to improve their characteristics and extend the functional capabilities of short-range autodyne radars. The experimental results obtained for the TIGEL 08FM oscillator module manufactured using a hybrid-integral technology on the basis of a mm-range Gunn diode are reported.

Parameter Optimization of Active Frequency Drift Islanding Detection Method

Abstract: Anti-islanding protection is mandatory feature for grid-connected inverters. Desired islanding detection method not only can detect islanding within acceptable duration,but also require it has less adverse impact on power quality. The performance of islanding detection method is usually subject to anti-islanding strategy and parameter setting. The paper analyzes non detection zone(NDZ) of active frequency drift(AFD) and active frequency drift with positive feedback(AFDPF) . Based on analysis the relationship between NDZ and feedback gain of AFDPF is deduced,which can be expressed as a mathematics equation and gives range for feedback gain to guarantee anti-islanding protection. The calculation is simple and accurate,thus can be taken as a good guideline in AFDPF parameters setting.

Improved frequency/voltage converters for fast quartz crystal microbalance applications.

Abstract: The monitoring of frequency changes in fast quartz crystal microbalance (QCM) applications is a real challenge in today’s instrumentation. In these applications, such as ac electrogravimetry, small frequency shifts, in the order of tens of hertz, around the resonance of the sensor can occur up to a frequency modulation of 1kHz. These frequency changes have to be monitored very accurately both in magnitude and phase. Phase-locked loop techniques can be used for obtaining a high performance frequency/voltage converter which can provide reliable measurements. Sensitivity higher than 10mV∕Hz, for a frequency shift resolution of 0.1Hz, with very low distortion in tracking both the magnitude and phase of the frequency variations around the resonance frequency of the sensor are required specifications. Moreover, the resonance frequency can vary in a broad frequency range from 5to10MHz in typical QCM sensors, which introduces an additional difficulty. A new frequency-voltage conversion system based on a double tuning analog-digital phase-locked loop is proposed. The reported electronic characterization and experimental results obtained with conducting polymers prove its reliability for ac-electrogravimetry measurements and, in general, for fast QCM applications.

Method and system for correcting oscillator frequency drift

Abstract: A method and apparatus for correcting oscillator frequency drift due to crystal aging. Correction signals that reflect a difference between an oscillator timing signal and a reference timing signal over a reference timing signal interval are modeled so that auxiliary correction signals can be generated in the event of loss of the reference timing signal. A temperature curve is generated to model how temperature variation impacts oscillator frequency drift. A rate of frequency drift due to crystal aging is also determined. During loss of a reference timing signal, auxiliary correction signals can be generated to maintain the oscillator at a desired frequency until the reference timing signal becomes available again.

Methods and systems for temperature related frequency drift compensation

Abstract: Systems and methods are provided that compensate for frequency drift due to temperature variation without the need for a temperature sensor. In one embodiment, a navigation receiver with an integrated communication device receives a base station reference signal, which is used to periodically calibrate a local oscillator frequency. In another embodiment, the calibrated local oscillator frequency drives a counter that is used to provide code phase estimation at the start of satellite signal acquisition. To provide temperature compensation in one embodiment, the calibrated local frequency is used to drive one or more counters at different calibration rates (i.e., different time intervals between calibrations). Count values from these counters are used to determine compensation for frequency drift due to temperature variation based on predicted frequency drift variation patterns between calibrations. This temperature compensation does not require a temperature sensor and further improves the accuracy of the code phase estimation.

PWM Controller with Frequency Jitter Functionality and Related Method

Abstract: A pulse width modulation controller with frequency jitter functionality includes an oscillator and a threshold voltage generator. The oscillator is utilized for generating a switching frequency signal according to an upper threshold voltage and a lower threshold voltage. The threshold voltage generator is coupled to the oscillator, and is utilized for generating the upper threshold voltage and the lower threshold voltage and modulating at least one of the upper threshold voltage and the lower threshold voltage to vary over time for jittering the switching frequency signal.