675 results about "Frequency drift" patented technology

A delay locked loop (DLL) according to the present invention includes a cycle time detector to determine the quantity of delay elements within a clock cycle and adjust a DLL counter controlling a DLL variable delay line to enable operation or locking in response to DLL overflow and underflow conditions. The cycle time detector includes a ring oscillator having a strong correlation between the oscillator period and the DLL delay elements. The output of the oscillator controls the counter to provide a new locking position for the DLL in the presence of overflow or underflow conditions. The oscillator is driven for an interval corresponding to the product of the external clock period and the quantity of delay elements in the ring oscillator. In effect, the delay of the DLL is adjusted to the preceding or succeeding external clock period to enable locking in response to overflow or underflow conditions.

In an OFDM transmission scheme, in order to compensate any frequency response variations time wise resulted from any distortion in a transmission path, out-of-synchronization with passage of time, frequency drift, and phase shift, and to improve a demodulation characteristic, a PS detector in a receiver receiving an OFDM signal detects a pilot symbol. A PS1 TPFR calculator calculates a frequency response of the transmission path for a first pilot symbol, while a PS2 TPFR calculators calculates a frequency response of the transmission path for a second pilot symbol for a second pilot symbol. Thereafter, a compensation vector calculator calculates compensation vectors from the frequency responses of the transmission path for both of the first and second pilot symbols by linear approximation. A frequency response compensatory compensates the frequency response variation of subcarriers in a data symbol based on the calculated compensation vectors.

A compensated ensemble crystal oscillator clock system for use in a well borehohe system. The clock system includes preferably four quad compensated clocks, a compensated temperature sensor, and software for processing and correcting system response. Physical fabrication of elements of the quad compensated clocks, the compensated temperature sensor and cooperating software minimized drift in frequency of the oscillator clock system in harsh borehole environments encountered while drilling a borehole. The clock system exhibits a frequency stability of 2.8×10−9 or less over a temperature range of from 0° C. to 185° C. The compensated ensemble crystal oscillator clock system is particularly applicable to seismic-while-drilling operations wherein precise downhole measurements of time are required typically over a period of days.

A method and system for cancelling body movement effect for non-contact vital sign detection is described. The method begins with sending on a first electromagnetic wave transceiver a first electromagnetic signal with a first frequency to a first side of a body, such as a person or animal. Simultaneously using a second electromagnetic wave transceiver a second electromagnetic signal is sent with a second frequency to a second side of a body, wherein the first frequency and the second frequency are different frequencies. A first reflected electromagnetic signal reflected back in response to the first electromagnetic wave on the first transceiver is received and a first baseband complex signal is extracted. Likewise a second reflected electromagnetic signal reflected back in response to the second electromagnetic wave on the second transceiver is received and a second baseband complex signal is extracted. The first baseband complex signal is mathematically combined with the second baseband complex signal to cancel out a Doppler frequency drift therebetween to yield a periodic Doppler phase effect.

An RC type oscillator (10) is integrated into a processor circuit (2) of a mobile device (1). This oscillator is used to set the pace of the activity of the processor circuit during periods when the mobile device is on standby. The frequency drift due to the temperature variations of the oscillator is concerted by a regular calibration of the oscillator by a faster oscillator recognized to be stable. This embodiment gives gain in space and a reduction in cost.

Techniques for direct modulation of a voltage-controlled oscillator (VCO) with adaptive digital gain control for wideband wireless applications are disclosed. A digital adaptive gain control loop is used to directly modulate the VCO, and a phase-locked loop (PLL) to track the frequency drift and other nonlinear effects of the VCO. As the PLL is applied to track the carrier frequency without passing the modulation signal into the PLL loop filter, the PLL can be implemented with a narrow loop bandwidth. The wideband frequency modulated signal is directly up-converted to the radio frequency (RF) signal by directly modulating the VCO through a digital-to-analog converter which is digitally controlled by an adaptive gain control loop. Thus, both wide bandwidth and low output noise for a frequency synthesizer and modulator can be achieved.

A system and method are described for providing drift compensation for a multimedia receiver which processes multimedia streams from a plurality of satellite transponders and / or cable / broadcast carriers. In one embodiment, the average drift amount for all multimedia signals in a first group of multimedia signals is calculated and, based on the calculation, the drift of the entire group is corrected. This drift is referred to as system drift. In addition, the difference in drift between each individual multimedia signal and the system drift amount is used to correct the individual drift for each multimedia signal.

An interference wave signal removing device that can surely remove an interference wave signal is provided. An interference wave signal remover includes a controller, a notch filter, an entire-range frequency scanner, and a local frequency scanner. The controller detects the interference wave signal based on a frequency scanning result by the entire-range frequency scanner, and sets the notch filter to attenuate the interference wave signal frequency. Based on input signals to the notch filter, the local frequency scanner frequency-scans in a local frequency band including an attenuation band of the notch filter. The controller detects a frequency drift of the interference wave signal frequency based on the frequency scanning result by the local frequency scanner, and updates the setting of the notch filter to attenuate the interference wave signal frequency after the frequency drift.

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.

A cascaded phase-locked loop (PLL) clock generation technique reduces frequency drift of a low-jitter clock signal in a holdover mode. An apparatus includes a first PLL circuit configured to generate a control signal based on a first clock signal and a first divider value. The apparatus includes a second PLL circuit configured to generate the first clock signal based on a low-jitter clock signal and a second divider value. The apparatus includes a third PLL circuit configured to generate the second divider value based on the first clock signal, a third divider value, and a second clock signal. The low-jitter clock signal may have a greater temperature dependence than the second clock signal and the second clock signal may have a higher jitter than the low-jitter clock signal.

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.

The invention discloses a method and a device for synchronizing clocks. The method comprises the following steps of: calculating frequency drift and time migration between a local clock and a master clock; calibrating the local clock by using the frequency drift, and calibrating second pulse signals by using the time migration; and synchronizing the time of work clocks and time stamp modules in physical layer chips by using TOD (time of date) of the calibrated local clock, the calibrated second pulse signals and the rising edge of the calibrated second pulse signals. According to the method and the device, the problem of low synchronization accuracy caused by nondeterminacy of network link delay introduced by the physical layer chips and asymmetry of duplex paths in the prior art is solved, and the time of a plurality of physical layer chips and the master clock is synchronized.

The invention discloses a frequency synthesizer comprising a frequency-locked loop which runs based on the reference frequency of a crystal oscillator, a frequency correction unit and an interpolation logic unit; wherein, the frequency correction unit generates a digital frequency correction control word based on a first parameter and a second parameter; the first parameter is a combination of an automatic frequency correction word and a fixed frequency control word. The interpolation logic unit is used for generating the second parameter which expresses the temperature changing compensation; wherein, when the first parameter is a constant, the frequency-locked loop generates a fixed clock signal or when the first parameter is a binary sequence which expresses the frequency changing of a modulating signal, the frequency-locked loop generates a frequency modulating signal; temperature compensation to the frequency excursion of a reference clock can be realized by controlling the frequency correction control word.

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.

The invention discloses an all-fiber direct detection anemometric laser radar system and a closed-loop control method thereof. The system comprises an optical emission part, a frequency locking part, an emission part and a receiving part, wherein the optical emission part is used for emitting a modulated and amplified laser pulse; the frequency locking part is used for detecting the laser frequency variation, feeding back to the laser emission part, adjusting the laser wavelength and further realizing the function of locking the laser wavelength according to the deviation; the emission part is used for enabling the laser beam to point to the detection zone of the atmosphere, coupling the atmospheric back scattered light to a receiver through an optical telescope and modulating the near field signal strength; the receiving part is used for filtering out sun background from a signal and dividing the signal into two paths, one path of signal passes through a Fabry-Perot interferometer, the other path of signal is used as energy reference, the transmittance is obtained through the ratio of the signal intensities of the two paths of signal, and the wind velocity is obtained through inversion according to Doppler frequency shift. The laser radar adopts an all-fiber structure and has the advantages of small size and light weight, the manufacturing cost of the radar is low, the laser radar is controlled through a 3-level closed-loop, and the environmental adaptability and working stability of the laser radar are improved.

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.

A clock recovery circuit in a digital display unit for recovering a time reference signal associated with analog display data. The clock recovery circuit includes a phase-locked loop (PLL) implemented in digital domain and an analog filter to eliminate any undesirable frequencies from the output signal of the PLL. The PLL includes independent control loops to track long term frequency drifts of the time reference signal and the transient phase differences respectively. By providing such independent control loops, the generated clock can be better synchronized with the time reference signal.

A phase detector for a phase-locked loop includes a phase detector that is configured to become unstable, oscillate and drift rapidly in frequency in a predictable manner when a reference frequency signal is not available. When applied, for example, to a power converter connected to a power distribution grid, the predictable oscillatory and rapid frequency drift behavior when the phase detector is unstable allows very rapid and reliable detection of disconnection from the grid, referred to as islanding.

Devices and methods for detecting islanding operation of a static power source involve injection of a non-harmonic error on the phase angle of the static power source in regular steps to introduce a very small intentional phase shift for the output voltage of the static power source in every voltage cycle which is corrected in each cycle in synchronization with the grid voltage in normal operation of the grid. In abnormal operation of a grid loss, this intentional small phase shift or error causes an intentional small frequency drift in each voltage cycle that continues in one cycle after another cycle. When the intentional frequency drift is over a preset level, a detection circuit starts to isolate the static power source from the grid to prevent islanding operation.

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.

Methods and systems for dynamically tuning and calibrating an antenna using on-chip digitally controlled array of capacitors are disclosed. Aspects of one method may include dynamically tuning a mobile terminal antenna (MTA) using on-chip arrays of capacitive devices. The tuning may be, for example, to compensate for center frequency drift during operation of the mobile terminal. The tuning may be accomplished by selecting capacitive devices in the on-chip arrays of capacitive devices to use in conjunction with an inductive circuit coupled to the MTA, where the inductive circuit may be either off the chip or on the chip. Accordingly, an impedance of the circuit formed by the capacitive devices in the on-chip arrays of capacitive devices and the inductive circuit may be adjusted with respect to the MTA. A valid circuit configuration may include a configuration where no capacitive device may be selected for use with the inductive circuit.

The invention involves a method of digital phase-locked loop for timestamp clock synchronization and equipment. Firstly, the server sends a value, which includes the message S (t) to timestamp, as the input synchronized signal. Take the time on which timestamp the server sent arriving at phase-locked loop as the recording time R (t) of local time. Then take the local timestamp according to the local clock frequency as reference input signal. The numerically controlled adjusts the output frequency according to ring circuit signal by filter. Lastly, the timestamp creater / recorder output the signal as the local clock frequency according to the output signal created by DOC. Under the condition that the invention use larger drift mobility and the lower stability oscillator, the system can provide high accuracy time synchronism.

The invention relates to the technical field of the optical fiber sensor, providing a phase-sensitive optical time domain reflectometer type optical fiber distributed disturbing sensor of double-arm pulse optical interference. By adopting a laser that is narrow in line width, large in power and low in frequency drift, the phase-sensitive optical time domain reflectometer type optical fiber distributed disturbing sensor of double-arm pulse optical interference provided by the invention based on the phase-sensitive optical time domain reflection technology can position the disturbing signals in a single point or multiple points simultaneously through interference of backward Rayleigh scattering light in two sensing arms pulse width areas by comparing the signals after and before disturbance. By extracting the phase information in a trigonometric function for large numbers accumulation or average, the invention improves the sensitivity of the system equivalently. The invention improves the sensitivity of the system by way of square or exponentiation. Finally, optimally, PGC (phase generated carrier) algorithm is used to extract the phase information so as to eliminate the influence of random change of scattered signals, thereby improving the sensitivity of the system equivalently.

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.

The invention discloses a magnetic field stabilizing method and device for a magnetic resonance imaging system. According to the magnetic field stabilizing method, a group of active compensating coils is arranged in a magnet, real-time magnetic field frequency drift amount is acquired, the current magnitudes and change rates of the active compensating coils are set, and the magnetic field change of a main magnet is compensated in real time by using a generated magnetic field, so that a total magnetic field is kept stable, and drift of the magnetic field is eliminated. The magnetic field stabilizing device comprises a group of active compensating coils (201) for generating a compensating magnetic field, a constant-current source (205) for driving the active compensating coils, and a constant-current-source controller (204) for controlling the current magnitude and direction of a constant current source. By adopting the method, the main magnetic field of the magnetic resonance imaging system can keep stable in a scanning process, and the quality of images is improved greatly.

The invention discloses a frequency drift compensation-based phase sensitive optical time domain reflectometer and a measuring method thereof. According to the system, a Mach-Zehnder interferometer (MZI) with fixed arm length difference is formed and a laser frequency drift detection module is formed by introducing time delay optical fiber and connecting optical fiber with specific optical path difference on the basis of the traditional phi-OTDR. The frequency drift of the layer is obtained according to the signal intensity of the MZI in the system and the phase position of a phi-OTDR sensingsystem is compensated through a phase compensation algorithm, so that the influence on the sensing property of the phi-OTDR by the frequency drift of the laser is eliminated. The influence on the sensing property by the frequency drift of the laser is eliminated by constructing a novel phi-OTDR system, the influence of noise can be reduced by processing methods such as phase compensation, and theaccuracy of quantitatively measuring a vibration event by the system is improved.

Using Brillouin reflectance technique in optical time domain adopted in the invention picks up strain information carried by Brillouin frequency drift caused by change of position information and temperature change carried in power of reflected light. Using method of combining absolute positioning with relative positioning makes successive approximation till exact location is determined finally. Comparing with prior art, the invention has features of omitting tedious calculation and additional data log, shortening time for finding out fault point of optical cable line so as to save cost. The method is general suitable method for positioning fault point applicable to optical cable line in position fixing direct burying type, aerial cable or duct optical cable.

The invention discloses an FBAR with a temperature compensation function and a resonance frequency tuning function and a filter. The FBAR comprises a substrate, a temperature compensation and resonance frequency tuning layer, a supporting layer, a bottom electrode, a top electrode and a piezoelectric film. The middle of the bottom of the temperature compensation and resonance frequency tuning layer is provided with a groove, the substrate is arranged under the two sides of the groove, and a cavity is formed through the substrate and the bottom face of the temperature compensation and resonance frequency tuning layer; the supporting layer is arranged on the upper side of the temperature compensation and resonance frequency tuning layer; the piezoelectric film is arranged between the bottom electrode and the top electrode; the FBAR and the filter can effectively reduce temperature and frequency drift caused by a piezoelectric film with a negative temperature coefficient, and accordingly the temperature stability of the FBAR is improved. In the post-processing technology, the thickness of an FBAR lamination is adjusted by controlling etching time of the temperature compensation and resonance frequency tuning layer in the FBAR lamination, frequency drift caused by process errors can be effectively reduced, and the frequency accuracy of the FBAR is improved.

The invention provides a method and apparatus to optimally estimate and adaptively compensate the temperature-induced frequency drift of a crystal oscillator in a navigational signal receiver. A Read-Write memory encodes two tables, one for looking up frequency drift values versus temperature readings and another one for valid data confirmation on the first table. The initially empty look-up table is gradually populated with frequency drift values while the receiver computes the frequency drift along with its position. During initial start of the receiver or re-acquisition of satellite signals, the stored frequency drift value corresponding to the current temperature is used. If no valid frequency drift value is available, the frequency drift value is computed based on the existing frequency drift values in the table. This invention reduces the Time-To-First-Fix (TTFF) of the receiver and enables the receiver to self-calibrate, thus no additional factory calibration would be necessary.

A resonator of a VCO includes a fine tuning main varactor circuit, an auxiliary varactor circuit, and a coarse tuning capacitor bank circuit coupled in parallel with an inductance. The main varactor circuit includes a plurality of circuit portions that can be separately disabled. Within each circuit portion is a multiplexing circuit that supplies a selectable one of either a fine tuning control signal (FTAVCS) or a temperature compensation control signal (TCAVCS) onto a varactor control node within the circuit portion. If the circuit portion is enabled then the FTAVCS is supplied onto the control node so that the circuit portion is used for fine tuning. If the circuit portion is disabled then the TCAVCS is supplied onto the control node so that the circuit portion is used to combat VCO frequency drift as a function of temperature. How the voltage of the TCAVCS varies with temperature is digitally programmable.