Showing papers on "Frequency drift published in 2003"

System and method for frequency management in a communications device having a positioning feature

Abstract: A frequency management scheme for a hybrid cellular/GPS or other device generates a local clock signal for the communications portion of the device, using a crystal oscillator or other part. The oscillator output may be corrected by way of an automatic frequency control (AFC) circuit or software, to drive the frequency of that clock signal to a higher accuracy. Besides being delivered to the cellular or other communications portion of the hybrid device, the compensated clock signal may also be delivered to a comparator to measure the offset between the cellular oscillator and the GPS oscillator. The error in the cellular oscillator may be measured from the AFC operation in the cellular portion of the device. An undershoot or overshoot in the delta between the two oscillators may thus be deduced to be due to bias in the GPS oscillator, whose value may then be determined. That value may then be used to adjust Doppler search, bandwidth or other GPS receiver characteristics to achieve better time to first fix or other performance characteristics.

CMOS ring oscillator with quadrature outputs and 100 MHz to 3.5 GHz tuning range

Abstract: A 100 MHz to 3.5 GHz four-stage CMOS ring oscillator with quadrature outputs and oscillator core current consumption roughly proportional to operating frequency is presented. A novel oscillator topology consisting of a chain of four static single-ended CMOS inverters, four additional feedforward inverters and frequency control by steering the total oscillator core current is proposed. The circuit is implemented in a 0.18/spl mu/ standard CMOS technology. Oscillator core current consumption is 90/spl mu/A at 100 MHz and 9mA at 3.5 GHz with a 1.8V supply. Measured phase noise at 4 MHz offset is -114dBc/Hz at 100MHz and -106dBc/Hz at 3.5GHz oscillation frequency. Quadrature error is better than 3.5/spl deg/ over the 100 MHz to 3GHz frequency range.

A method to derive an equation for the oscillation frequency of a ring oscillator

Abstract: A new method for deriving an equation for the oscillation frequency of a ring oscillator is proposed. The method is general enough to be used for a variety of types of delay stages. Furthermore, it provides a framework to include various parasitic and secondary effects. The method is used to derive an equation for a common ring oscillator topology. The validity of the method and the resulting equation have been verified through simulation. The oscillation frequencies predicted by the proposed method are more accurate than existing equations and account for more secondary effects.

Frequency entrainment for micromechanical oscillator

Abstract: We demonstrate synchronization of laser-induced self-sustained vibrations of radio-frequency micromechanical resonators by applying a small pilot signal either as an inertial drive at the natural frequency of the resonator or by modulating the stiffness of the oscillator at double the natural frequency. By sweeping the pilot signal frequency, we demonstrate that the entrainment zone is hysteretic and can be as wide as 4% of the natural frequency of the resonator, 400 times the 1/Q∼10−4 half-width of the resonant peak. Possible applications are discussed based on the wide range of frequency tuning and the power gain provided by the large amplitude of self-oscillations (controlled by a small pilot signal).

Solar type IV burst spectral fine structures - I. Observations

Abstract: The fine structures (FS) of solar type IV radio bursts are of principal interest for flare plasma diagnostics in the low corona In this paper we give an observational (Part I) and theoretical (Paper II) treatment of broad band radio pulsations (BBP) and zebra patterns (ZP) in a well observed flaring sigmoidal loop system of AR 7792 on 25 October 1994 We present comprehensive meter-decimeter radio spectral (Astrophysical Institute Potsdam, AIP) and meter wave heliographic (Nancay Radio Heliograph of Paris-Meudon Observatory, NRH) observations Spectral and spatial properties of FS elements (one pulsation pulse, one single zebra stripe) as well as a statistical analysis for the whole fine structure event are presented The source sites are compared with soft X-ray images of the flare, and with force-free extrapolated coronal magnetic fields Both FS sources occur in a common diverging loop structure with a turning height of about 70 Mm The BBP source is shown to appear (if seen along the loop axis) nearer to the injection site of the electrons than the ZP source BBP do show high frequency drift (-250 MHz s - 1 ) At a given frequency, the projected source speed is 11 x 10 5 km s - 1 For ZP, we find a good correlation between the inclination of a single zebra stripe to the heliographic observing frequency level in the dynamic spectrogram, and the speed of the simultaneously observed projected source motion at this frequency The direction of the source motion at a given frequency is on average found to be perpendicular between BBP and ZP sources During a time interval of 90 s the BBP source consists in its lower part (higher observing frequencies) of a widely spaced double source Despite a source distance of 360 Mm both subsources are highly correlated and thus probably simultaneously driven We come to the conclusion that both fine structures are emitted during repeated electron beam injection into an asymmetric magnetic trap configuration between a footpoint in the leading spot of AR 7792 and a trailing more dispersed footpoint In Paper II we will show that the specifications derived from the data allow for selecting one out of several competing fine structure models which explains the simultaneous formation of BBP and ZP in the same loop structure

Method and apparatus for compensating an oscillator in a location-enabled wireless device

Abstract: A method and apparatus for compensating an oscillator in a location-enabled wireless device is described. In an example, a mobile device includes a wireless receiver for receiving wireless signals and a GPS receiver for receiving GPS signals. The mobile device also includes an oscillator having an associated temperature model. A frequency error is derived from a wireless signal. The temperature model is adjusted in response to the frequency error and a temperature proximate the oscillator. Frequency error of the oscillator is compensated using the adjusted temperature model. In another example, a frequency error is derived using a second oscillator within the wireless receiver.

A Kalman Filter Clock Algorithm for Use in the Presence of Flicker Frequency Modulation Noise

Abstract: The National Physical Laboratory (NPL) has developed a Kalman filter based algorithm for combining measurements from its three active hydrogen masers. The algorithm is designed to produce a near optimal composite clock when the dominant noise process of at least one of the masers is flicker frequency modulation (FFM), and significant linear frequency drift is exhibited. The FFM is modelled approximately by a linear combination of Markov noise processes. Each Markov process is included in the Kalman filter and contributes an additional component to the state vector. Both the validity of the model and the effectiveness of adding these additional components are examined. The performance of the new algorithm is investigated when applied to simulated measurements and also to measurements obtained from NPL's hydrogen masers.

Optoelectronic oscillator with improved phase noise and frequency stability

Abstract: In this paper we report on recent improvements in phase noise and frequency stability of a 10 GHz opto-electronic oscillator. In our OEO loop, the high Q elements (the optical fiber and the narrow bandpass microwave filter) are thermally stabilized using resistive heaters and temperature controllers, keeping their temperature above ambient. The thermally stabilized free running OEO demonstrates a short-term frequency stability of 0.02 ppm (over several hours) and frequency vs. temperature slope of −0.1 ppm/°C (compared to -8.3 ppm/°C for non thermally stabilized OEO). We obtained an exceptional spectral purity with phase noise level of -143 dBc/Hz at 10 kHz of offset frequency. We also describe the multi-loop configuration that reduces dramatically the spurious level at offset frequencies related to the loop round trip harmonic frequency. The multi-loop configuration has stronger mode selectivity due to interference between signals having different cavity lengths. A drop of the spurious level below −90 dBc was demonstrated. The effect of the oscillator aging on the frequency stability was studied as well by recording the oscillator frequency (in a chamber) over several weeks. We observed reversal in aging direction with logarithmic behavior of A ln(B t+1)-C ln(D t+1), where t is the time and A, B, C, D are constants. Initially, in the first several days, the positive aging dominates. However, later the negative aging mechanism dominates. We have concluded that the long-term aging behavioral model is consistent with the experimental results.

Anti-islanding device and method for grid connected inverters using random noise injection

Abstract: A device and method for detecting islanding of a grid connected inverter makes use of an injected white noise as a perturbing force on the output voltage of the inverter. The white noise is injected at least once in every cycle and can be generated at different rates in implementation. On loss of the grid, a frequency drift of the output voltage is detected and a positive feedback is activated that accelerates the drift.

Systems and methods for providing an adjustable reference signal to RF circuitry

Abstract: Frequency modification circuitry may be employed as part of a crystal oscillator circuit to generate a reference signal with adjustable frequency. The frequency modification circuitry may be implemented as part of a crystal oscillator circuit that includes digitally controlled crystal oscillator (“DCXO”) circuitry and a crystal. The frequency modification circuitry may adjust the frequency of the reference signal in response to one or more frequency control signals. In one example, the frequency modification circuitry may include variable capacitors such as one or more continuously variable and/or discretely variable capacitors for providing coarse and/or fine adjustment of the reference signal frequency.

Phase-locked loop with automatic frequency tuning

Abstract: A PLL frequency synthesizer able to automatically set an appropriate operating mode of (Q) voltage controlled oscillator (4) is provided. The voltage controlled oscillator (4) is operable in a plurality of operating modes each defining a different operating frequency range of the voltage controlled oscillator. The appropriate operating mode is selected based on an error signal detected by a phase/frequency detector (1) of the PLL frequency synthesizer. A window comparator (13) is used for switching to adjacent operating modes if the error signal exceeds or falls below predefined upper and lower error voltage limits.

Torsion oscillator stabilization

Abstract: A torsion oscillator (FIG. 1 ) is stabilized in operation by determining the current resonant frequency ( 62 ); in a first procedure, observing the oscillator for change in resonant frequency ( 64 ), and then restoring the amplitude and median offset ( 66 ) without changing the drive frequency. In an alternative procedure, after determining the resonant frequency ( 62 ); setting the drive frequency close to but offset from the current resonant frequency ( 74 ), observing the oscillator for change in resonant frequency ( 76 ), and the restoring the close offset to the changed resonant frequency ( 78 ). By operating slightly off peak, the direction of resonant change is immediately known. The first procedure has less difficulties in implementation, but requires more power.

Indirect temperature compensation process in an oscillator

Abstract: A temperature compensation technique is disclosed which allows to obtain a compensated clock signal. The temperature compensation technique comprises the use of a thermal model of the oscillator with a temperature sensor in order to accurately compute the oscillator frequency, irrespective of time-variations and rates.

System and method for oscillator self-calibration using AC line frequency

Abstract: A self-calibrating radio frequency transmitter includes an adjustable oscillator, a first frequency counter, a second frequency counter, and a comparer. The radio frequency transmitter is powered by an AC power line, which presents a line frequency. The transmitter contains an adjustable frequency oscillator that oscillates at an oscillator frequency and has a desired operating frequency. The first frequency counter counts the oscillator frequency while the second frequency counter counts the line frequency. The comparer compares the counted oscillator frequency to the counted line frequency and produces an output representative of the difference between the counted line frequency and the counted oscillator frequency. This difference in frequency indicates a deviation in the oscillator frequency from the desired operating frequency. The output from the comparer is input to the oscillator to adjust the oscillator frequency back to the desired operating frequency.

Trimming of a two point phase modulator

Abstract: Method and system are disclosed for automated calibration of the VCO gain in phase modulators. The method and system of the invention comprises synthesizing, in a phase modulator, a signal having a given output frequency using a controlled oscillator having a frequency control input, a modulation input, and a feedback loop. A frequency control signal is applied to the frequency control input, and gain variation of the controlled oscillator is compensated for outside of the feedback loop via the modulation input. The method and system of the invention may be employed in any telecommunication system that uses phase and amplitude modulation, including EDGE and WCDMA systems.

Temperature compensation for a variable frequency oscillator without reducing pull range

Abstract: A variable frequency oscillator having multiple, independent frequency control inputs, each coupled to a respective tuning sub-circuit. The tuning sub-circuits are connected in parallel with each other and with a resonator module, which may be a quartz crystal, inductor, or other reactance component. Each tuning sub-circuit consists of two varactors with their respective cathodes coupled to each other and to their corresponding frequency control input. By having the tuning sub-circuits connected in parallel to the resonator, the overall frequency pull range of each frequency control input remains unaffected by the activation of any other frequency control input. Preferably, at least one frequency control input is a temperature compensation control input that can maintain the variable oscillator insensitive to temperature variations while the remaining frequency control inputs provide functional frequency control.

Capture range control mechanism for voltage controlled oscillators

Abstract: A voltage controlled oscillator generates an output signal whose frequency varies as a first function of a control voltage applied to a control terminal. The voltage controlled oscillator has a wide range of frequency of operation. A gain adjust circuit adjusts the gain of the voltage controlled oscillator such that the first function varies as a second function of the gain. In a preferred embodiment the gain adjust circuit includes a variable impedance that may be external or integrated onto a common chip with the oscillator core.

Design and characterization of an all-cryogenic low phase-noise sapphire K-band oscillator for satellite communication

Abstract: An all-cryogenic oscillator consisting of a frequency-tunable sapphire resonator, a high-temperature superconducting filter and a pseudomorphic high electron-mobility transistor amplifier was designed for the K-band frequency range. The high quality factor of the resonator above 1 000 000 and the low amplifier phase noise of approximately -133 dBc/Hz at a frequency offset of 1 kHz from the carrier, gave oscillator phase-noise values superior to quartz-stabilized oscillators at the same carrier frequency for offset frequencies higher than 100 Hz. In addition to low phase noise, the oscillator possesses mechanical and electrical frequency tunability. We have implemented a two-step electrical tuning arrangement consisting of a varactor phase shifter integrated within the amplifier circuit (fine tuning by 5 kHz) and a dielectric plunger moved by a piezomechanical transducer inside the resonator housing (coarse tuning by 50 kHz). This tuning range is sufficient for phase locking and for electronic compensation of temperature drifts occurring during operation of the device employing a miniaturized closed-cycle Stirling-type cryocooler.

Direct automatic frequency control method and apparatus

Abstract: An Automatic Frequency Control (AFC) circuit for a mobile terminal employs a fractional-N Phase Locked Loop (PLL) to directly reduce errors in the synthesized frequency, such as due to component tolerances, temperature drift, and the like. The frequency error is detected by the average speed of rotation of the I,Q constellation. A corresponding offset is added to the tuning frequency selection word prior to encoding, such as in a ΔΣ modulator, to generate an effective non-integer PLL frequency division factor over a specified duration. The ΔΣ modulator may include dithering the different integer values by a pseudo-random number to minimize noise in the output frequency spectrum introduced by the fractional-N division. Component and parameter selection allow a high degree of resolution in frequency control of the fractional-N PLL. By directly controlling for the frequency error, a DAC and XTAL oscillator tuning circuit may be eliminated from the AFC circuit.

A 1-V 2.4-GHz PLL synthesizer with a fully differential prescaler and a low-off-leakage charge pump

Abstract: A 1 V 2.4 GHz-band fully monolithic PLL synthesizer was fabricated using 0.2 /spl mu/m CMOS/SOI process technology. It includes a voltage controlled oscillator (VCO) and a 3 GHz fully differential dual-modulus prescaler on a chip. A low-off-leakage-current charge pump is used for open-loop FSK modulation. When the PLL is in open loop mode, the frequency drift of the output is lower than 2.5 Hz//spl mu/sec. The output phase noise is -104 dBc/Hz at 1 MHz offset frequency. The power consumption of the PLL-IC core is 17 mW at 1 V supply voltage.

Slow drift mirror modes in finite electron-temperature plasma: Hydrodynamic and kinetic drift mirror instabilities

Abstract: [1] We develop a fully kinetic linear theory of the drift mirror (DM) instability accounting for arbitrary particle velocity distribution functions including nonzero electron temperature effects and plasma pressure anisotropy. In the quasi-hydrodynamic limiting case the theory reproduces the results obtained for the ion mirror instability. However, for the very low frequency electron DM modes which can develop in a nonuniform plasma of nonzero electron temperature, Te ≠ 0, such an equivalence does not exist. We refer to these modes as slow drift mirror (SDM) modes in order to distinguish them from the conventional ion-DM mode. Two new instabilities, one hydrodynamic and one kinetic, that lead to the growth of SDM modes are found in the fully kinetic regime. The first instability develops for values of the ion anisotropy lower than required for the classical ion-DM instability. The second instability occurs when the conditions for the ion-DM instability are satisfied as well. The frequency of the SDM mode is less than the frequency of the ion-DM mode, ω ≪ ωDM ∼ ωn, where ωn is the density gradient-drift frequency of the ions. However, when the electron temperature is of the order of the parallel ion temperature, the SDM instability growth rate may become comparable or even higher than that of the ion-DM instability. The free energy necessary for these new instabilities is taken from two sources. The main source is the energy stored in the ion pressure anisotropy. The second source is the electron pressure gradient which builds up in a plasma of nonzero electron temperature.

Ring oscillator with frequency stabilization

Abstract: A current-controlled ring oscillator (300) uses a single controlled-current supply for supplying current to each inversion stage (110) of the ring oscillator (300). The controlled current is dynamically adjusted to compensate for variations in process, voltage, or temperature conditions. A relatively simple circuit (350) is used to generate the controlled current that supplies all of the inversion stages (110) over a wide range of process, voltage, and temperature variations.

New wideband/dualband CMOS LC voltage-controlled oscillator

Abstract: A wideband voltage-controlled oscillator (VCO) with a frequency range from 830 MHz to 2.4 GHz is presented. The VCO has two control inputs, one for continuous control of the output frequency and one for band switching, and two quadrature outputs. Based on a 0.25 /spl mu/m CMOS process, this VCO is simulated for the supply voltage of 2 V. A wide tuning range of 98% is obtained in two independent bands. The harmonic distortions are kept low enough within the entire frequency range. The phase noise is -105 dBc/Hz at 400 kHz offset for the oscillation frequency of 830 MHz, and -89 dBc/Hz at 400 kHz offset for the oscillation frequency of 2.42 GHz. The VCO has a gain of 745.6 MHz/V for its first band and 1.22 GHz/V for its second band. Accurate quadrature outputs are maintained throughout the entire frequency range, as needed in all modern transceiver architectures. Its 2nd harmonic is also reduced by a compensation circuit to less than -33 dB in the worst case at the frequency of 2.42 GHz

Phase and frequency drift compensation in Orthogonal Frequency Division Multiplexing systems

Abstract: A phase drift compensation scheme for multi-carrier systems According to the invention, a timing offset compensator is provided to compensate for a timing offset in a current symbol after taking an N-point FFT Then a phase estimator computes a phase estimate for the current symbol based on a function of a channel response of each pilot subcarrier, transmitted data on each pilot subcarrier, and a timing compensated version of the current symbol on the pilot subcarrier locations From the phase estimate, a tracking unit can generate a phase tracking value for the current symbol Thereafter, a phase compensator uses the phase tracking value to compensate the timing compensated version of the current symbol for the effect of phase drift

PLL circuit including a voltage controlled oscillator and a method for controlling a voltage controlled oscillator

Abstract: A voltage controlled oscillator having a wide oscillation frequency band, desirable carrier-noise characteristic, and desirable linearity of the oscillation frequency relative to a control voltage. The voltage controlled oscillator includes an oscillation unit and a control unit. The oscillation unit generates an output signal having an oscillation frequency corresponding to the control voltage in one of a plurality of oscillation frequency bands. The oscillation unit includes a switching unit for selecting one of the plurality of oscillation frequency bands in accordance with a switching signal. The control unit generates the switching signal in accordance with the control voltage.

Method for AM band interference suppression via frequency shift

Abstract: Methods are provided for suppressing interference in a motor vehicle radio such as an AM radio from the operating frequency or the harmonics of the operating frequency of a source of time varying signal such as a switching power supply in response to tuning the radio to a selected frequency. The method comprises the steps of communicating the selected frequency to the source of time varying signal, comparing the selected frequency to the operating frequency and to the harmonics of that operating frequency, and adjusting the operating frequency if the operating frequency or any of the harmonics of the operating frequency fall within a predetermined interference range of the selected frequency.

High Frequency Model of Transformer Winding

Abstract: A high frequency model of transformer winding is used to analyze the voltage oscillations due to various excitations such as the very fast transient overvoltage which occurs at the time of disconnecting switch operations. Usually, a circuit of interlinked inductances and capacitances is used for this purpose, in which circuit parameters have to be properly determined. Previously, those constants have been estimated taking the coil section pair as a unit. In the method proposed here, the section pair can be further subdivided. The time-domain calculation is conducted combining the frequency analysis and FFT technique. The voltage oscillations of the winding subjected to the lightning impulse are calculated. The correspondence with the experimental results is satisfactory. The response to a chopped impulse shows this method's applicability to high frequency analysis. Since the constants are calculated directly from the design parameters of transformer winding, this technique is particularly useful in developing and designing transformers. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(3): 8–16, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10280

Spectral-temporal evolution of low-frequency pulsations in the microwave radiation of solar flares

Abstract: Low-frequency pulsations of 22 and 37 GHz microwave radiation detected during solar flares are analyzed. Several microwave bursts observed at the Metsahovi Radio Observatory are studied with time resolutions of 100 and 50 ms. A fast Fourier transformation with a sliding window and the Wigner-Ville method are used to obtain frequency-time diagrams for the low-frequency pulsations, which are interpreted as natural oscillations of coronal magnetic loops; the dynamical spectra of the pulsations are synthesized for the first time. Three types of low-frequency fluctuations modulating the flare microwave radiation can be distinguished in the observations. First, there are fast and slow magneto-acoustic oscillations with periods of 0.5–0.8 s and 200–280 s, respectively. The fast magneto-acoustic oscillations appear as trains of narrow-band signals with durations of 100–200 s, a positive frequency drift dν/dt=0.25 MHz/min, and frequency splitting δν=0.01–0.05 Hz. Second, there are natural oscillations of the coronal magnetic loops as equivalent electrical circuits. These oscillations have periods of 0.5–10 s and positive or negative frequency drift rates dν/dt=8×10−3 Hz/min or dν/dt=−1.3×10−2 Hz/min, depending on the phase of the radio outburst. Third, there are modulations of the microwave radiation by short periodic pulses with a period of 20 s. The dynamical spectra of the low-frequency pulsations supply important information about the parameters of the magnetic loops: the ratio of the loop radius to its length r/L≈0.1, the plasma parameter β≈10−3, the ratio of the plasma densities outside and inside the loop ρe/ρi≈10−2, and the electrical current flowing along the loop I≈1012 A.

Unilateral coupling for a quadrature voltage controlled oscillator

Abstract: According to some embodiments, unilateral coupling is provided for a quadrature voltage controlled oscillator. For example, a first voltage controlled oscillator may be provided with a 0 degree phase node and a 180 degree phase node A second voltage controlled oscillator may be provided with a 90 degree phase node and a 270 degree phase node. In addition, the first and second voltage controlled oscillators may be mutually coupled with substantially unilateral cascaded common-source common-gate amplifier coupling devices to create a quadrature voltage controlled oscillator.