Showing papers on "Frequency drift published in 2014"
TL;DR: In this paper, the effects of frequency drift on Gamma-Aminobutyric acid (GABA+)-edited MRS of the human brain at 3 Tesla (T) were investigated.
Abstract: Purpose: To investigate the quantitative impact of frequency drift on Gamma-Aminobutyric acid (GABA+)-edited MRS of the human brain at 3 Tesla (T).
Methods: Three sequential GABA+-edited MEGA-PRESS acquisitions were acquired in fifteen sessions; in ten of these, MRS was preceded by functional MRI (fMRI) to induce frequency drift, which was estimated from the creatine resonance at 3.0 ppm. Simulations were performed to examine the effects of frequency drift on the editing efficiency of GABA and co-edited macromolecules (MM) and of subtraction artifacts on GABA+ quantification. The efficacy of postprocessing frequency correction was also investigated.
Results: Gradient-induced frequency drifts affect GABA+ quantification for at least 30 min after imaging. Average frequency drift was low in control sessions and as high as −2 Hz/min after fMRI. Uncorrected frequency drift has an approximately linear effect on GABA+ measurements with a −10 Hz drift resulting in a 16% decrease in GABA+, primarily due to subtraction artifacts.
Conclusion: Imaging acquisitions with high gradient duty cycles can impact subsequent GABA+ measurements. Postprocessing can address subtraction artifacts, but not changes in editing efficiency or GABA:MM signal ratios; therefore, protocol design should avoid intensive gradient sequences before edited MRS Magn Reson Med 72:941–948, 2014.
94 citations
TL;DR: In this article, the authors investigated the long-term performance of an ultrastable laser system that is stabilized to a single-crystal silicon cavity operated at 124 k. Utilizing a frequency comb, the laser was compared to a hydrogen maser that is referenced to a primary caesium fountain standard and to the Sr87 optical lattice clock at Physikalisch-Technische Bundesanstalt.
Abstract: Cryogenic single-crystal optical cavities have the potential to provide high dimensional stability. We have investigated the long-term performance of an ultrastable laser system that is stabilized to a single-crystal silicon cavity operated at 124 K. Utilizing a frequency comb, the laser is compared to a hydrogen maser that is referenced to a primary caesium fountain standard and to the Sr87 optical lattice clock at Physikalisch-Technische Bundesanstalt (PTB). With fractional frequency instabilities of σy(τ)≤2×10−16 for averaging times of τ=60 s to 1000 s and σy(1 d)≤2×10−15 the stability of this laser, without any aid from an atomic reference, surpasses the best known microwave standards for short averaging times and is competitive with the best known hydrogen masers for longer times of 1 day. The comparison of modeled thermal response of the cavity with measured data indicates an average fractional frequency drift below 5×10−19/s, which we do not expect to be a fundamental limit.
54 citations
TL;DR: In this article, a wavelet packet transform (WPT) based location scheme for phase-sensitive optical time-domain reflectometry (OTDR) is proposed, which is insensitive to the frequency drift of the laser.
50 citations
TL;DR: In this article, the authors present a complete characterization of a laser setup for rubidium cooling dedicated to space applications, which is realized with commercial off-the-shelf fiber components suitable for space applications.
Abstract: We present the complete characterization of a laser setup for rubidium cooling dedicated to space applications. The experimental setup is realized with commercial off-the-shelf fiber components suitable for space applications. By frequency doubling two fiber laser diodes at 1560 nm, we produce the two optical frequencies at 780 nm required for atomic cooling of 87Rb. The first laser is locked on saturated absorption signal and long-term frequency drift has been canceled using a digital integrator. The optical frequency of the second laser is controlled relatively to the first one by a frequency comparison method. A full characterization of the setup, including frequency stability evaluation and frequency noise measurement, has been performed. The optical frequency doubling module has been submitted to environmental tests to verify its compatibility with space applications.
49 citations
TL;DR: The simulation results show that the FRC grows with increasing frequency drift rate and pulse width, reaches, and maintains the peak value when the frequency Drift rate and/or the pulse width are high enough, which is useful for choosing laser sources and improving the performance of φ-OTDR.
Abstract: This paper investigates the influences of laser source on distributed intrusion sensor based on a phase-sensitivity optical time-domain reflectometer (φ-OTDR). A numerical simulation is performed to illustrate the relationships between trace-to-trace fluctuations and frequency drift rate as well as pulse width, and fluctuations ratio coefficient (FRC) is proposed to evaluate the level of trace-to-trace fluctuations. The simulation results show that the FRC grows with increasing frequency drift rate and pulse width, reaches, and maintains the peak value when the frequency drift rate and/or the pulse width are high enough. Furthermore, experiments are implemented using a φ-OTDR prototype with a low frequency drift laser (<5 MHz/min), of which the high frequency drift rate is simulated by frequency sweeping. The good agreement of experimental with simulated results in the region of high frequency drift rate validates the theoretical analysis, and the huge differences between them in the region of low frequency drift rate indicate the place of laser frequency drift among system noises. The conclusion is useful for choosing laser sources and improving the performance of φ-OTDR.
43 citations
TL;DR: A novel scheme to generate broadband high-repetition-rate optical frequency combs and low phase noise microwave signals simultaneously is proposed and experimentally demonstrated.
Abstract: A novel scheme to generate broadband high-repetition-rate optical frequency combs and low phase noise microwave signals simultaneously is proposed and experimentally demonstrated. By incorporating an optical frequency comb generator in an optoelectronic oscillator loop, more than 200 lines are generated for a 25 GHz optical frequency comb, and the single-sideband phase noise is as low as −122 dBc/Hz at 10 kHz offset for the 25 GHz microwave signal. 10 and 20 GHz optical frequency combs and microwave signals are also generated. Unlike the microwave frequency synthesizer, the phase noise of the microwave signals generated by this new scheme is frequency independent.
39 citations
06 Mar 2014
TL;DR: The THz/sub-mm-Wave band is known to provide unique applications in spectroscopy, imaging and high-data-rate wireless communication, and the need for precise oscillation frequency with wide tuning range and low close-in phase noise calls for closed-loop topologies.
Abstract: The THz/sub-mm-Wave band is known to provide unique applications in spectroscopy, imaging and high-data-rate wireless communication. An accurate THz source is essential in coherent communications, radar systems, and frequency metrology. Recently, THz sources based on coupled VCOs with harmonic generation have been proposed [1]. However, open-loop signal sources exhibit severe frequency fluctuation, and are vulnerable to temperature/process/supply-induced frequency drift. The need for precise oscillation frequency with wide tuning range and low close-in phase noise calls for closed-loop topologies. Millimeter-Wave PLLs incorporating push-push VCOs have been demonstrated up to 164GHz [2] in silicon technology. [3] presented a 300GHz PLL with 0.12% locking range in III-IV technology.
33 citations
TL;DR: In this article, the authors report observations of slowly drifting pulsating structures (DPS) in the 0.8-4.5 GHz frequency range of the RT4 and RT5 radio spectrographs at Ondrejov observatory, between 2002 and 2012.
Abstract: We report observations of slowly drifting pulsating structures (DPS) in the 0.8-4.5 GHz frequency range of the RT4 and RT5 radio spectrographs at Ondrejov observatory, between 2002 and 2012. We found 106 events of drifting pulsating structures, which we classified into 4 cases: (I) single events with a constant frequency drift [12 events], (II) multiple events occurring in the same flare with constant frequency drifts [11 events], (III) single or multiple events with increasing or decreasing frequency drift rates [52 events], and (IV) complex events containing multiple events occurring at the same time in the different frequency range [31 events]. Many DPSs are associated with hard X-ray bursts (15-25 keV) and soft X-ray gradient peaks, as they typically occurred at the beginning of the hard X-ray peaks. This indicates that DPS events are related to the processes of fast energy release and particle acceleration. Furthermore, interpreting DPSs as signatures of plasmoids, we measured their ejection velocity, their width and their height from the DPS spectra, from which we also estimated the reconnection rate and the plasma beta. In this interpretation, constant frequency drift indicates a constant velocity of a plasmoid, and an increasing/decreasing frequency drift indicates a deceleration/acceleration of a plasmoid ejection. The reconnection rate shows a good positive correlation with the plasmoid velocity. Finally we confirmed that some DPS events show plasmoid counterparts in AIA/SDO images.
30 citations
TL;DR: The technique that combines saturated-absorption spectroscopy and Zeeman splitting of hyperfine structures allows us to obtain a modulation-free dispersion-like error signal for frequency stabilization, and an available sub-Doppler DAVLL error signal with high sensitivity to the frequency drift is obtained.
Abstract: We achieve laser frequency stabilization by a simple technique based on sub-Doppler dichroic atomic vapor laser lock (DAVLL) in atomic cesium. The technique that combines saturated-absorption spectroscopy and Zeeman splitting of hyperfine structures allows us to obtain a modulation-free dispersion-like error signal for frequency stabilization. For the error signal, the dependence of peak-to-peak amplitude and the slope at the zero-crossing point on the magnetic field is studied by simulation and experiment. Based on the result, we obtain an available sub-Doppler DAVLL error signal with high sensitivity to the frequency drift by selecting an appropriate strength of the magnetic field. Ultimately, the fluctuation of the locked laser frequency is confined to below 0.5 MHz in a long term, exhibiting efficient suppression of frequency noise.
30 citations
TL;DR: In this article, an external cavity diode laser was reported to have a linear frequency drift of 25 mHz/s, which was the lowest ever reported with ULE glass.
Abstract: An external cavity diode laser stabilized to a high-finesse rigid cavity made of ultralow-expansion (ULE) glass maintained at a zero-crossing temperature of −3.3 °C showed a linear frequency drift of 25 mHz/s, which was the lowest ever reported with ULE glass. The linewidth of the beat note between two independent laser systems stabilized to independent ULE glass cavities was narrower than 1 Hz, and the Allan deviation of the beat note around 1 s of averaging time was close to the Brownian thermomechanical noise limit.
28 citations
TL;DR: In this article, a Fabry-Perot etalon with a finesse of 100 000 was used as a photonic filter in a single loop optoelectronic oscillator, which provided narrow bandwidth microwave filtering at harmonics of its 1.5 GHz free spectral range for oscillation in the range of 6 to 60 GHz.
Abstract: A Fabry-Perot etalon with a finesse of 100 000 is used as a photonic filter in a single loop optoelectronic oscillator. The etalon provides narrow bandwidth microwave filtering at harmonics of its 1.5 GHz free spectral range for oscillation in the range of 6 to 60 GHz. Fiber delays as long as 2 km are added to the loop with no spurious modes visible above the noise floor. The environmental stability of the etalon makes it suitable as a secondary reference for feedback to the optical frequency which contributes to the reduction of phase noise and long term frequency drift.
TL;DR: In this article, the authors proposed a feedback control loop that detects the oscillator frequency using a frequency discriminator and modifies the laser wavelength to keep the frequency constant using the fiber chromatic dispersion.
Abstract: A new method for the long-term frequency stabilization of an opto-electronic oscillator (OEO) is proposed. All existing methods are based on the precise temperature stabilization of specific components of an OEO, for example, the optical fiber and the microwave band-pass filter. We propose a new method based on a feedback control loop that detects the oscillator frequency using a frequency discriminator and modifies the laser wavelength to keep the oscillator frequency constant using the fiber chromatic dispersion. With the proposed method we achieved a frequency-temperature coefficient of 0.2 ppm/K. Unlike previous methods, our method also compensates the effects of other unstabilized OEO components on the OEO's frequency. Other benefits are that there is no need for an accurate temperature stabilization of the optical fiber and mode hopping is prevented.
TL;DR: A fiber-based stable radio frequency transfer system by a hybrid frequency modulation scheme that combines two radio frequency signals combined and simultaneously transferred by only one laser diode is proposed.
Abstract: In this Letter, we propose a fiber-based stable radio frequency transfer system by a hybrid frequency modulation scheme. Creatively, two radio frequency signals are combined and simultaneously transferred by only one laser diode. One frequency component is used to detect the phase fluctuation, and the other one is the derivative compensated signal providing a stable frequency for the remote end. A proper ratio of the frequencies of the components is well maintained by parameter m to avoid interference between them. Experimentally, a stable 200 MHz signal is transferred over 100 km optical fiber with the help of a 1 GHz detecting signal, and fractional instability of 2×10−17 at 105 s is achieved.
Patent•
19 Mar 2014
TL;DR: In this article, a micro-grid islanding detection method is proposed, where the authors install a device node for implanting an improved active frequency drift method at a common connection point of a microgrid and a main grid; setting threshold values of voltage and frequency, injecting disturbing current with the disturbance factor of K0 into a system in real time, detecting the voltage UPCC and the frequency f of the common connected point, and judging that islanding happens when the voltage upCC or the frequency exceeds the threshold values; performing next discrimination if the voltage or frequency f does not
Abstract: A micro-grid islanding detection method includes the steps: installing a device node for implanting an improved active frequency drift method at a common connection point of a micro-grid and a main grid; setting threshold values of voltage and frequency, injecting disturbing current with the disturbance factor of K0 into a system in real time, detecting the voltage UPCC and the frequency f of the common connection point, and judging that islanding happens when the voltage UPCC or the frequency f exceeds the threshold values; performing next discrimination if the voltage UPCC or the frequency f does not exceed the threshold values, comparing the current frequency fin of the injected grid with grid voltage frequency fgrid under a normal condition by a comparison circuit, and determining load characteristics; calculating a disturbance factor K in positive feedback application according to the load characteristics to generate final disturbing signals; transmitting the disturbing signals to an inverter of a distributed power generation system by a PWM (pulse width modulation) driving module, disconnecting a grid-connected circuit breaker when the frequency and the voltage of the common connection point are changed to trigger over/under frequency and over/under voltage detection due to islanding, and stopping power supply for a load by the inverter until the grids return to normal
TL;DR: A microwave photonic frequency measurement system is demonstrated practically, using the four-wave mixing effect in a highly nonlinear fiber to produce a low-frequency output voltage, which is a function of input RF frequency.
Abstract: A microwave photonic frequency measurement system is demonstrated practically. The system employs the four-wave mixing effect in a highly nonlinear fiber to produce a low-frequency output voltage, which is a function of input RF frequency. Using an algorithm that allows dynamic reconfiguration, the system is able to instantaneously monitor a broad frequency range for threat signals and to provide fast yet accurate frequency measurement. An operating frequency range of 0.04–40 GHz with at most 0.016% error is achieved.
TL;DR: In this article, a photonic assisted radio frequency (RF) down-converter integrating with the optoelectronic oscillator (OEO)-based high quality local oscillator was proposed and experimentally demonstrated.
Abstract: A photonic-assisted radio frequency (RF) down-converter integrating with the optoelectronic oscillator (OEO)-based high quality local oscillator (LO) has been proposed and experimentally demonstrated. The LO and the RF input signal are mixed at the same phase modulator and photo-detector (PD) of the OEO-loop without any additional modulator or PD. The working bandwidth of the proposed RF down-converter is nearly from 2.5 to 10 GHz. The performance of the proposed down-converter is presented and the spurious frequency dynamic range at frequency of 5.5 GHz with the LO at 6.138 GHz is measured to be 98.4 dB–Hz2/3. The influences that the frequency range and power of the RF input signal bring to the system are discussed as well.
TL;DR: In this paper, a fast wavelength-tunable burst-mode receiver for coherent 28 GBd dual-polarization quadrature phase shift keying signals using a commercially available DS-DBR laser as the local oscillator (LO) was demonstrated.
Abstract: We demonstrate a fast wavelength-tunable burst-mode receiver for coherent 28 GBd dual-polarization quadrature phase shift keying signals using a commercially available DS-DBR laser as the local oscillator (LO). We find that the frequency drift and linewidth of the LO must be precisely controlled to prevent bit-error-ratio (BER) penalties when the signal undergoes transmission distances typical of metropolitan-area networks. We demonstrate reduction of the LO frequency drift and linewidth after wavelength switching by compensation using the phase section of the laser and achieve negligible BER penalty with burst-mode reception for single-mode fiber transmission up to 1280 km. We also measure the sensitivity of the receiver to LO detuning when multiple wavelength-division multiplexed channels are received simultaneously as in a broadcast-and-select network architecture.
TL;DR: In this article, the authors present an analysis of several Jovian Io-related decametric radio storms recorded in 2004−2012 at the Ukrainian array UTR-2 using the new generation of baseband digital receivers.
Abstract: We present an analysis of several Jovian Io-related decametric radio storms recorded in 2004−2012 at the Ukrainian array UTR-2 using the new generation of baseband digital receivers. Continuous baseband sampling within sessions lasting for several hours enabled us to study the evolution of multiscale spectral patterns during the whole storm at varying time and frequency resolutions and trace the temporal transformation of burst structures in unprecedented detail. In addition to the well-known frequency drifting millisecond patterns known as S bursts we detected two other classes of events that often look like S bursts at low resolution but reveal a more complicated structure in high resolution dynamic spectra. The emissions of the first type (LS bursts, superposition of L and S type emissions) have a much lower frequency drift rate than the usual quasi linearly drifting S bursts (QS) and often occur within a frequency band where L emission is simultaneously present, suggesting that both LS and at least part of L emissions may come from the same source. The bursts of the second type (modulated S bursts called MS) are formed by a wideband frequency-modulated envelope that can mimic S bursts with very steep negative (or even positive) drift rates. Observed with insufficient time-frequency resolution, MS look like S bursts with complex shapes and varying drifts; MS patterns often occur in association with (i) narrowband emission; (ii) S burst trains; or (iii) sequences of fast drift shadow events. We propose a phenomenological description for various types of S emissions, that should include at least three components: high- and low-frequency limitation of the overall frequency band of the emission, fast frequency modulation of emission structures within this band, and emergence of elementary S burst substructures, that we call “forking” structures. All together, these three components can produce most of the observed spectral structures, including S bursts with apparently very complex time-frequency structures.
Patent•
26 Mar 2014
TL;DR: In this article, a buck switching regulator implements a fixed frequency feedback control circuit including a voltage control loop and a frequency control loop to regulate the switching frequency of the regulator to a fixed or nearly fixed frequency.
Abstract: A buck switching regulator implements a fixed frequency feedback control circuit including a voltage control loop and a frequency control loop to regulate the switching frequency of the buck switching regulator to a fixed or nearly fixed frequency. The voltage control loop, implementing ripple mode control, is configured to control the power switches in response to the switching regulator output voltage or a signal related to the switching regulator output voltage. The frequency control loop, implementing a phase-locked loop control scheme, is configured to adjust the on-time of the high-side switch so as to regulate the switching frequency to be equal to or be proportional to the reference frequency.
TL;DR: In this article, the identical parameters describing the radio sources for zebra structures (ZSs) and fiber bursts confirm there is a common mechanism for both structures, and the selection of the radio emission mechanism for fast broadband pulsations with millisecond duration also depends on the parameters of their radio sources.
Abstract: The measurement of positions and sizes of radio sources in the observations of the fine structure of solar radio bursts is a determining factor for the selection of the radio emission mechanism. The identical parameters describing the radio sources for zebra structures (ZSs) and fiber bursts confirm there is a common mechanism for both structures. It is very important to measure the size of the source in the corona to determine if it is distributed along the height or if it is point-like. In both models of ZSs (the double plasma resonance (DPR) and the whistler model) the source must be distributed along the height, but by contrast to the stationary source in the DPR model, in the whistler model the source should be moving. Moreover, the direction of the space drift of the radio source must correlate with the frequency drift of stripes in the dynamic spectrum. Some models of ZSs require a local source, for example, the models based on the Bernstein modes, or on explosive instability. The selection of the radio emission mechanism for fast broadband pulsations with millisecond duration also depends on the parameters of their radio sources.
TL;DR: In this paper, a novel frequency compensation circuit for adaptive on-time control buck regulator is presented, which mainly applied to provide power supply for double data rate synchronous dynamic random access memory system.
Abstract: A novel frequency compensation circuit for adaptive on-time control buck regulator is presented in this study, which mainly applied to provide power supply for double data rate synchronous dynamic random access memory system. Typical ripple control regulator possesses the advantage of fast transient response and unconditional stability. However, it suffers significant steady-state switching frequency variation when the input voltage and output voltage are varied. The on-time is directly proportional to the output voltage and inversely proportional to the input voltage so that the regulator can dynamically adjust the turn-on time of power switches according to the changes of input voltage and output voltage in steady-state operation by adaptive on-time control. Finally, an approximately fixed switching frequency is achieved. However, the variation of the switching frequency with load current still exists. Through the implementation of the frequency compensation circuit, the switching frequency variation caused by the load current variation can be effectively reduced in order to obtaining a more fixed switching frequency. The adaptive on-time control regulator with frequency compensation has been successfully fabricated with 0.35 µm 30 V complementary double-diffused metal oxide semiconductor process and full chip test results are provided to verify the proposed method in this study.
04 May 2014
TL;DR: In this paper, a new small-signal model for the modulation frequency response of a Si micro-ring modulator is proposed based on the coupled-mode theory and has the well-known second-order system characteristics.
Abstract: We present a new small-signal model for the modulation frequency response of a Si micro-ring modulator. The model is based on the coupled-mode theory and has the well-known second-order system characteristics. The accuracy of the model is confirmed with measured Si MRM small-signal frequency response.
30 May 2014
TL;DR: In this article, a multi-resonator system capable of generating a temperature-stable frequency reference across a wide temperature range is presented, which involves the use of a minimum of three temperature-compensated oscillators having a slightly different turnover temperature.
Abstract: This work reports on a multi-resonator system capable of generating a temperature-stable frequency reference across a wide temperature range. The system involves the use of a minimum of three temperature-compensated oscillators having a slightly different turnover temperature. The oscillator output frequency undergoes frequency multiplication and mixing in two stages to achieve a temperature-stable frequency output. The sensitivity of the clock frequency is analyzed as a function of temperature induced measurement errors. AlN-on-silicon ring resonators actuated piezoelectrically are proposed as the three frequency setting components. Their turnover temperature is controlled through the placement of oxide within the resonator volume. A total frequency shift of less than 10 ppm is estimated across the temperature range of -40 °C to 85 °C with this implementation.
TL;DR: A frequency standard based on a detuned coherent population beating phenomenon, where the beat frequency of the radio frequency for laser modulation and the hyperfine splitting can be obtained by digital signal processing technology.
Abstract: We demonstrated a frequency standard based on a detuned coherent population beating phenomenon. In this phenomenon, the beat frequency of the radio frequency for laser modulation and the hyperfine splitting can be obtained by digital signal processing technology. After analyzing the spectrum of the beat frequency, the fluctuation information is obtained and applied to compensate for the frequency shift to generate the standard frequency by the digital synthesis method. Frequency instability of 2.6 × 1012 at 1000 s is observed in our preliminary experiment. By eliminating the phase-locking loop, the method will enable us to achieve a full-digital frequency standard with remarkable stability.
TL;DR: Two GPS receiver clock models are introduced to describe the deterministic and stochastic property of the receiver clock, both of which can improve the accuracy of kinematic orbit determination for spacecraft in low earth orbit.
TL;DR: In this article, the operation of rotary traveling wave oscillators is analyzed, the general oscillation condition is derived, and analytical formula for the oscillator loss is presented based on this analysis, switched transmission line is employed to extend the output frequency tuning range.
Abstract: In this paper, the operation of rotary traveling wave oscillators is analyzed, the general oscillation condition is derived, and analytical formula for the oscillator loss is presented. Based on this analysis, switched transmission line is employed to extend the output frequency tuning range. Post-layout simulation shows a frequency tuning range of 3.1 GHz in the vicinity of 30 GHz. The proposed half-quadrature VCO exhibits a phase noise better than −102.2 dBc/Hz at 1 MHz offset frequency. The VCO provides an output power level ranging from −6 to −2.5 dBm with drawing 15.2 mA of dc current from a 1.8 V power supply.
TL;DR: A novel hybrid islanding detection method for inverter-based distributed generation (DG) based on frequency drift is proposed, which is a combination of Sandia frequency-shift, reactive power versus frequency and reactive power deviation as active methods, and over/under frequency protection as a passive method.
Abstract: This paper proposes a novel hybrid islanding detection method for inverter-based distributed generation (DG) based on frequency drift. This algorithm is a combination of Sandia frequency-shift, reactive power versus frequency and reactive power deviation as active methods, and over/under frequency protection as a passive method. The performance of the proposed method is evaluated under the UL 1741 anti-islanding tests configuration, IEEE 1547, load switching, load quality factor and multiple-DG operation. The simulation results are derived by MATLAB/ Simulink. Based on simulation results, it is clear that the proposed method is developed to detect islanding more efficiently for loads with high quality factor. The proposed method also has less non-detection zone comparing other methods. In addition, the proposed method operates accurately in condition of load switching while does not interfere with the power system operation during normal conditions. This technique proves to be robust under multiple-DG operation.
Patent•
13 Aug 2014
TL;DR: In this article, an island detection method based on the combination of phase mutation and active frequency drift is proposed, which is used to detect an island in large-scale new energy centralized grid connection, where the phase difference delta phi between grid connection output current of an inverter and voltage of a public coupling point and the frequency f of the voltage of the coupling point is detected.
Abstract: The invention discloses an island detection method based on the combination of phase mutation and active frequency drift, and belongs to the field of anti-islanding protection of large-scale new energy centralized grid connection. The island detection method based on the combination of phase mutation and active frequency drift comprises the steps that (1) the phase difference delta phi between grid connection output current of an inverter and voltage of a public coupling point and the frequency f of the voltage of the public coupling point are detected; (2) whether the delta phi is larger than phi is judged, if yes, the step (5) is executed, and if not, the step (1) is executed again; whether the f is smaller than fmin or larger than fmax is judged, if yes, the step (5) is executed, and if not, the step (3) is executed; (3) frequency disturbance is added to the grid connection output current of the inverter through the active frequency drift technology in every period, and the frequency f' of the voltage of the public coupling point is detected; (4) whether the f' is larger than the fmax is judged, if yes, the step (5) is executed, and if not, the step (1) is executed again; (5) an island protection action is adopted. The island detection method based on the combination of phase mutation and active frequency drift resolves the problem that a single passive detection method fails under the condition of a resistance-similar load, has no detection blind area, and can effectively detect an island.
03 Nov 2014
TL;DR: An original mmW frequency multiplier that provides a 58.32 GHz to 62.64 GHz LO starting from a much lower and fixed frequency of 2.16 GHz is presented, with a record phase noise of -104 dBc/Hz @ 1MHz offset.
Abstract: This paper presents an original mmW frequency multiplier that provides a 58.32 GHz to 62.64 GHz LO starting from a much lower and fixed frequency of 2.16 GHz. It is composed of a pulsed VCO, which generates equally spaced harmonics in the 60 GHz band, and an injection locked oscillator (ILO) that selects the harmonic of interest. The CMOS 40nm circuit consumes 32 mW and occupies only 0.07 mm2. This novel programmable multiplication technique requires a unique fixed low frequency reference to perform multi-channel mmW LO generation. The phase noise of the output LO signal is only limited by the input low frequency reference phase noise and the frequency ratio between output and input signals. Thus, a 60 GHz signal has been generated with this technique with a record phase noise of -104 dBc/Hz @ 1MHz offset.
19 May 2014
TL;DR: In this article, a wide-range linear analog controller has been implemented to reduce the effective TCF of the fused silica resonator by an order of magnitude, and a digital calibration method is used to mitigate offset errors caused by non-ideal temperature sensing.
Abstract: In this paper, we report on temperature-stable operation of silica MEMS oscillators on an ovenized fused silica platform. Temperature servo-control circuits are implemented using an on-chip RTD-based temperature sensor and a resistive heater. A wide-range linear analog controller has been implemented to reduce the effective TCF of the fused silica resonator by an order of magnitude. Digital calibration method is used to mitigate offset errors caused by non-ideal temperature sensing. By effectively removing the offset errors, the frequency drift of an oscillator using a silica micromechanical resonator is reduced to less than 11 ppm over 105 °C of external temperature change. The power consumption to ovenize the entire platform consisting of four resonators is lower than 15.8 mW.