235 results about "Frequency correction" patented technology

The invention discloses an emergency power supply quick access method based on scene recognition, which relates to the technical field of emergency power supplies, and comprises the following steps: in an emergency power supply system, firstly obtaining electrical input parameter information through a preset detection frequency; by introducing a load change evaluation mechanism based on machine learning, the system can identify load fluctuation in real time and dynamically adjust the detection frequency, and the response speed to the rapid change of the load is improved. Compared with a traditional detection method, the load state is intelligently evaluated and accurately divided, it is ensured that the power factor is adjusted in time when the load fluctuates violently, and power loss and waste are reduced. Correction is carried out according to the traditional frequency during stable load fluctuation, the frequency is dynamically adjusted during rapid fluctuation, the electric energy use is optimized, the electric power quality is improved, and harmonic distortion and overload risks are reduced.

The invention relates to the technical field of electric power reactive power compensation, in particular to a novel static dynamic reactive power compensation device and a control method thereof, and the device comprises a power grid state monitoring module, a reactive power demand calculation module, a compensation control execution module, a harmonic suppression module and a dynamic energy storage support module. According to the method, through real-time extraction and segmented analysis of the dynamic operation parameters of the power grid, accurate perception of the state of the power grid is realized, the transient characteristics of operation are represented, an accurate basis is provided for subsequent compensation, decomposition and classified accumulation of reactive power requirements are realized, inductive and capacitive power differences are accurately identified, the calculation accuracy and efficiency are improved, and load adaptation is optimized; in harmonic suppression, resolution and response speed are enhanced through signal separation and frequency correction, energy storage and compensation linkage is improved through dynamic energy storage optimization, dynamic response capability is enhanced, loss is reduced, voltage stability and power factors are improved, stable guarantee is provided for complex fluctuation scenes, and electric energy is saved.

The invention discloses a tracking processing method for a baseband signal of a receiver, which comprises the following steps of: firstly, performing frequency correction through a frequency-locked loop, and performing phase correction through a phase-locked loop to realize accurate synchronization of carrier frequency and phase; then bit synchronization processing and incoherent integration are carried out, and the output signal-to-noise ratio of the loop and the measurement precision of the code phase are improved; and finally, the local pseudo-random code generator generates a local pseudo-random code, then the local pseudo-random code generator outputs three paths of pseudo-random codes which are mutually delayed by half a chip, namely a lead code, a real-time code and a lagging code, correlation values of the three paths of pseudo-random codes are obtained, a code phase error is obtained by calculating the correlation value difference of the lead code and the lagging code, and the local pseudo-random code is obtained. And after the code phase error is processed by a loop filter, an adjustment amount of a digital control oscillator is generated, so that the phase of the local pseudo-random code is adjusted. According to the invention, continuous adjustment of the digital control oscillator of the local carrier and the pseudo-random code is realized, so that correct navigation data information is demodulated for positioning calculation.

The invention provides a multi-motor pulse speed regulation control method and system, and relates to the technical field of motor control, the method comprises the steps that a target set quantity and a target motor identifier are obtained, a target driving parameter is obtained through conversion according to a parameter set associated with the target motor identifier, and the parameter set comprises an elastic modulus value and a stress relaxation coefficient of a peristaltic pump hose; real-time driving parameters are maintained for the multiple pulse output channels respectively, and refreshing is carried out at the synchronization moment; operating state feedback values of a peristaltic pump channel and a stirring motor channel are collected, a water hammer effect frequency component and an impeller passing frequency component are extracted, and correction is carried out based on the elastic parameters; and judging whether a cross-channel resonance judgment condition is met or not, and when the condition is met, determining a frequency correction amount and a phase correction amount and applying the correction amounts to at least one pulse output channel, thereby reducing the resonance risk and stabilizing the system operation.

The invention discloses an optical remote sensing satellite high and low frequency relative radiation error correction method and system, and the method comprises the steps: S1, carrying out the systematic high frequency radiation error calibration of a remote sensing image, so as to eliminate stripe noise; s2, performing frequency domain decomposition on the image after high-frequency correction, and separating high and low frequency components; s3, calculating a global statistical moment of the low-frequency component as a correction reference; s4, calculating a local statistical moment of the low-frequency component column by column; s5, calculating an independent correction coefficient for each column according to the global and local statistical moments; s6, correcting the low-frequency component by using the correction coefficient; and S7, recombining the corrected low-frequency component with the original high-frequency component to generate a final image. The method is suitable for improving the quality of the remote sensing image with multiple composite radiation errors, high-frequency stripes and low-frequency brightness gradient can be effectively eliminated, original texture details of ground features are reserved to the maximum extent in the correction process, and the radiation fidelity is guaranteed.

The invention relates to the technical field of data center energy storage and power supply, and discloses a flywheel AFE energy storage and power supply system for a data center, which comprises a flywheel energy storage unit, an AFE control module, a hierarchical energy scheduling module, a dynamic balance adjustment module and a feedback optimization module. The flywheel energy storage unit constructs a multi-stage energy buffer topology through a rotating speed monitoring node and a kinetic energy conversion network; the AFE control module realizes steady-state and transient-state control by using a multi-mode switching link of the vector modulation unit and inhibits harmonic waves in combination with the direct-current bus compensation unit; the hierarchical energy scheduling module generates a bus voltage reference strategy through a dynamic coordination model of the master control coordination node, and load power supply priorities are sorted through a dynamic priority distribution unit. The dynamic equalization adjustment module realizes power phase synchronization compensation and modulation frequency correction, and the feedback optimization module corrects a power supply strategy based on a closed loop of a bus harmonic evaluation network. The system improves the power supply stability, efficiency and reliability of the data center.

Systems and methods for packet-based network clock synchronization are provided. An integrated circuit device may include a local clock and a packet-based synchronization servo to apply a control loop to synchronize the local clock with a remote clock. The control loop may include a frequency correction to accelerate convergence.

The invention discloses a medium-frequency transformer insulation electrothermal aging evaluation method, a test device and a storage medium, and relates to the technical field of power transformers. The medium-frequency transformer insulation electric heating aging test device comprises a function signal generator, a high-voltage power amplifier, a protection and isolation unit, an electric-heat combined aging oven and a detection and monitoring unit. The electrothermal aging evaluation method comprises the following steps: acquiring an aged sample, testing the ultimate tensile strength and polymerization degree of the aged sample, introducing a frequency correction factor to correct an attenuation constant under a power frequency condition, establishing tensile strength attenuation equations under different frequencies, and evaluating the tensile strength of the aged sample. And respectively fitting the maximum value of the accumulated loss rate and the change rate of the accumulated loss rate under different frequencies to obtain a polymerization degree accumulated loss rate improvement formula, and carrying out aging characteristic analysis on the insulation of the intermediate-frequency transformer according to the actual working condition of the insulation of the intermediate-frequency transformer. According to the technical scheme, the blank of medium-frequency transformer insulation electrothermal aging research is filled.

The invention discloses a ground-based radar calibration deviation estimation method based on satellite-ground precipitation radar verification, and the method mainly comprises the steps: carrying out the frequency correction of a satellite-borne radar SR reflectivity factor from a Ku wave band to an S wave band, and carrying out the projection conversion of a polar coordinate system with a ground-based radar GR as a center after the correction; the converted SR and GR reflectivity factors are subjected to overlapping matching in time and space which are accurate to seconds; the mean value precision is improved through inverse distance weight, and the precipitation space heterogeneity of SR and GR in the matching space is reduced through the in-pixel non-uniform beam filling quality control technology; a satellite-ground precipitation radar quality control factor threshold standard system is established, whole-process quality control is carried out in the calibration deviation estimation process, and finally ground-based radar GR calibration deviation estimation is realized through comparison verification of spaceborne radar SR and ground-based radar GR reflectivity factors after quality control processing. According to the invention, the error of satellite-ground radar inspection can be effectively reduced, and the precision of rainfall estimation is improved.

The invention relates to a method and a system for ultrasonically characterizing a medium. The method comprises the following steps: generating a series of incident ultrasonic waves; measuring a regular reflection matrix Rui (t) defined between the input transmit basis (i) and the output receive basis (u); determining a set of responses R of the medium obtained for a plurality of points in the region around the reference point at a plurality of frequencies f based on a regular reflection matrix Rui (t); determining a frequency correction rule, phi, suitable for the reference point and determined at the frequency f, based on the response of the medium at the plurality of points; for the plurality of frequencies f, a corrected response R'of the medium is determined by applying a frequency correction rule Phi to the response R of the medium around the reference point.

A correction circuit for a switching converter counters undesired reduction of switching frequency in response to a decrease in a load current at a converter output node. Detection circuitry receives a reference clock signal indicative of a lower bound for the switching frequency of the converter and a pulsed drive signal indicative of the switching frequency of the converter. In response to the switching frequency of the converter falling below said lower bound for the switching frequency of the converter, the detection circuitry produces an error signal. Current sink circuitry coupled to the output node of the converter sinks from the output node of the converter corrective current in response to receipt of the error signal from the detection circuitry.

The invention provides a segmented adaptive gain-based short-wave band amplitude and phase control device and method, and relates to the field of short-wave intelligent control. The method comprises the following steps: performing coupling detection processing on N paths of input short-wave signals to obtain coupled short-wave signals and power values of the coupled short-wave signals; based on the coupled short-wave signal and the power value of the coupled short-wave signal, calculating adjustment parameters through a preset adaptive segmented multi-target differential evolution algorithm, wherein the adjustment parameters comprise a frequency correction parameter, a phase adjustment parameter and an amplitude control voltage; adjusting the coupled short-wave signal based on the adjustment parameter to obtain a target short-wave signal; and detecting whether the target short wave signal meets a preset output condition, and if the target short wave signal meets the preset output condition, coupling the target short wave signal to output a radio frequency output signal. Through the scheme, the communication quality is improved.

The invention discloses a resonant frequency identification and suppression method and system for a mechanical-gear-free integrated vernier motor, belongs to the field of mechanical-gear-free integrated vernier motor control, and is suitable for robot joint driving, high-precision servo systems and other scenes. The invention relates to a resonant frequency on-line rapid identification method, which comprises the following steps of: introducing an additional control degree of freedom into a traditional second-order generalized integrator-frequency-locked loop, optimizing an orthogonal signal generation process, and shortening convergence time in combination with an adaptive frequency correction link; the problems that a traditional resonant frequency identification algorithm is poor in identification accuracy and low in convergence speed are solved. According to the high-performance resonance suppression strategy, disturbance is estimated in real time through a linear expansion state observer; parameter setting is simple, the problem that multi-parameter setting of a traditional wave trap is complex is solved, and the strong-robustness resonance suppression effect under load inertia changes is achieved.

A rotating machine rotating speed self-adaptive estimation method based on harmonic energy and a maximum proportion criterion comprises the steps that firstly, multi-channel vibration signals are obtained through sampling, a channel signal with the maximum effective value is obtained to serve as a target signal for rotating speed estimation, and the target signal is pre-processed in a self-adaptive mode according to the signal type; secondly, Fourier transform is carried out on the preprocessed signals, a maximum value method is adopted to search for main spectrum peaks and frequency positions of the main spectrum peaks in an amplitude spectrum, and harmonic energy and proportions of all frequencies are calculated; and finally, searching the frequency corresponding to the maximum harmonic energy and proportion, performing frequency correction to obtain an accurate rotating frequency, and performing conversion calculation to obtain the rotating speed. The method effectively overcomes the defect that a traditional rotating speed estimation method is easily influenced by the power frequency amplitude, achieves accurate measurement of the steady-state rotating speed of equipment in a rotating speed sensor-free mode, can be suitable for displacement, speed, acceleration and other vibration sensors, and has the advantages of being simple in logic, wide in application range, high in estimation precision and the like.

A hybrid controller and method for mitigating frequency disturbances in a multi-area power plant including multiple thermal energy generators and renewable energy sources includes a cascaded fractional model predictive controller (CFMPC), first and second fractional-order proportional-integral-derivative controllers (FOPID-1 and FOPID-2) and a sooty terns controller. The CFMPC generates a minimized area central error (ACE) signal based on minimizing a controlled fitness equation, an ACE signal and a load power disturbance signal (ΔPL). The FOPID-1 generates a frequency disturbance correction signal based on the frequency disturbance value (Δfi). A combined frequency correction signal is generated by adding negative values of the minimized ACE signal and the frequency disturbance correction signal. The FOPID-2 receives the combined frequency correction signal and generates a frequency error correction signal. The sooty terns controller generates optimized gain parameters and transmits the optimized parameters to the FOPID-1 and the FOPID-2 to mitigate the frequency disturbances.

The invention discloses a high-precision liquid level measuring device and method based on sweep frequency interference measurement, belongs to the technical field of optical-mechanical-electrical integrated measurement, and is used for high-precision liquid level measurement. The light path is composed of a frequency sweep correction light path and a measurement calibration light path. The device comprises a sweep-frequency light source, an optical fiber splitter, a high-speed acquisition card, a computer, an optical fiber circulator, an optical fiber reflector, a Fabry-Perot (FP) etalon, a balanced photoelectric detector (BPD), a liquid level measuring probe and the like. The FP etalon realizes a sweep frequency correction function, a measurement calibration light path switches channels through the one-to-two photoelectric switch, and high-speed signal acquisition is carried out through the BPD and the high-speed acquisition card. The measuring process is free of mechanical movement and has the advantage of being free of maintenance; the FP etalon is introduced for nonlinear frequency sweeping calibration, the measurement precision is improved, the micron-level measurement precision can be achieved under the better experiment condition, and the non-contact measurement method can meet the requirement for high-precision liquid level measurement in the fields of chemistry, chemical engineering and the like.

The invention provides an anti-noise interference frequency parameter estimation method for high-precision optical coherence ranging, which comprises the following steps: acquiring a spectral interference signal of an optical low-coherence interference system and a reference light spectral signal output only by a reference arm, and converting the spectral interference signal into interference signals with wave number space arranged at equal intervals, carrying out spectral density amplitude normalization to obtain a standard interference signal so as to eliminate interference of light source spectrum fluctuation and non-uniform sampling on frequency estimation; hanning window modulation is applied to a standard interference signal, spectrum leakage is suppressed, spectrum analysis is performed on the modulated signal, a peak value and an adjacent secondary peak value of a spectrum main lobe are extracted, a frequency correction amount is calculated based on a peak value and secondary peak value amplitude ratio relation derived by a Hanning window spectrum mode function, and an accurate frequency of the interference signal is obtained; and calculating the displacement of the object to be measured according to the product of the accurate frequency and the spectral resolution of the optical low-coherence interference system in combination with the refractive index of the light in the measurement medium.

The invention relates to a satellite-ground radar reflectivity factor consistency evaluation and deviation traceability method and system, and belongs to the field of radar calibration evaluation, and the method comprises the steps: generating reference ground radar scanning parameters according to geographical environment multi-source heterogeneous data; acquiring satellite-ground radar data according to the scanning parameters of the reference ground-based radar when the satellite-borne radar passes the scene, and performing preprocessing and space-time matching to obtain a satellite-ground radar data pair; based on the target correction information of each height level region, performing sectional frequency correction on the spaceborne radar data to obtain an optimal satellite-ground radar data pair; and carrying out reflectivity factor consistency evaluation on the optimal satellite-ground radar data pair, taking an obtained evaluation result as a tracing reference, and carrying out deviation tracing calibration estimation on the service ground-based radar in combination with a satellite-ground radar reflectivity factor consistency evaluation result of the service ground-based radar. According to the method, the technical problems of precise evaluation of systematic deviation of satellite-ground radar data and unified evaluation and calibration of multi-service satellite-ground radars are solved.

An example method performed at a mobile device for position determination may comprise receiving from a server correction data associated with (1) a first pseudorange measurement of a first GNSS signal sent from a satellite vehicle on a first GNSS carrier frequency and (2) a second pseudorange measurement of a second GNSS signal sent from the satellite vehicle on a second GNSS carrier frequency. The method also may comprise measuring a third GNSS signal sent from the satellite vehicle and received at the mobile device on a third GNSS carrier frequency, to generate a third pseudorange measurement. The method also may comprise determining the position of the mobile device using (a) the third pseudorange measurement of the third GNSS signal on the third GNSS carrier frequency and (b) the correction data. The correction data received from the server may include a virtual pseudorange measurement for the third GNSS carrier frequency.

The invention discloses a microwave-assisted terahertz frequency offset compensation method, and aims to solve the problem of signal distortion caused by frequency offset in terahertz communication. According to the method, a microwave signal is introduced as an auxiliary reference to realize real-time estimation and compensation of terahertz emission signal frequency offset. The specific process comprises the steps of injection of a microwave reference signal, spectrum analysis of a receiving end, offset extraction and frequency correction of a baseband signal. Compared with a traditional frequency offset compensation scheme, the method can effectively improve the precision and stability of system frequency synchronization, reduce the hardware complexity and enhance the anti-interference capability of a communication system, has a good application prospect, and is particularly suitable for a terahertz wireless communication system with high frequency width and high rate.

A method for adjusting audio frequency includes steps of: obtaining initial frequency and temporary data storage of audio data input to a buffering unit; performing a first adjustment procedure on initial frequency to obtain a first variation of temporary data storage corresponding to a first change of initial frequency; calculating a first frequency correction amount according to first variation and a first period of first adjustment procedure; adjusting initial frequency into first frequency according to first frequency correction amount; inputting first frequency into buffering unit; performing a second adjustment procedure on first frequency to obtain a second variation of temporary data storage corresponding to a second change of first frequency; calculating a second frequency correction amount according to second variation and a second period of second adjustment procedure, which first period is less than second period; and adjusting first frequency into target frequency according to second frequency correction amount.

The invention discloses a time-frequency offset tracking method in a Tiantong satellite monitoring low-orbit satellite system, which belongs to the field of satellite communication, and comprises the following steps: acquiring satellite orbit information, satellite ephemeris information and positioning information of a low-orbit satellite, and resolving current Doppler frequency offset information; performing frequency pre-compensation according to the Doppler frequency offset information, and performing compensation by using the frequency offset captured by the FCCH; the satellite-borne terminal receiver carries out carrier frequency estimation by using a downlink channel, so that the carrier residual frequency difference of a received signal is estimated, and frequency correction is carried out; starting downlink timing tracking; uplink frequency offset compensation is started, so that the frequency of a signal from the low-orbit satellite to the Tiantong satellite is the expected carrier frequency of the Tiantong satellite; and carrying out transmission timing correction by adopting the spaceborne terminal timing drift rate, and carrying out uplink timing adjustment. According to the method, normal access and stable data transmission of the satellite-borne terminal can be realized.

A contactless electric power transmission system includes an electric power reception device and a control device. The electric power reception device receives AC electric power transmitted in a contactless manner from an electric power transmission device. The control device includes: a coil temperature detection portion that acquires temperatures of a secondary side coil, a magnetic member, and a secondary side capacitor of the electric power reception device; a magnetic member temperature detection portion; and a capacitor temperature detection portion. The control device includes a request frequency correction portion that corrects a request frequency of electric power transmission by the electric power transmission device based on the temperatures of the secondary side coil, the magnetic member, and the secondary side capacitor.

The invention discloses a county isolated network frequency correction control system supported by multiple resources cooperatively, which relates to the technical field of intelligent power grids and comprises a control center, and the control center is connected with a resource acquisition module, a cooperative processing module, a support analysis module and an intelligent correction module. Constructing a power grid comprehensive layout map, collecting power grid composite data, extracting an isolated grid regional frequency to construct a regional frequency dynamic graph, and performing frequency tense judgment on the regional frequency dynamic graph to obtain an isolated grid frequency judgment result; performing frequency measurement updating on the power grid comprehensive layout diagram to obtain an abnormal power grid marking diagram; performing anomaly grading on the abnormal power grid mark graph to obtain a node frequency deviation degree, and performing frequency supplementary rescue on the isolated network block according to the node frequency deviation degree to obtain a dynamic correction scheme; the frequency control capability is improved and the power system stability is enhanced.

The application discloses a frequency divider-free phase-locked loop and a reference double-delay frequency locking method thereof. The sub-sampling phase-locked loop architecture receives an output of an oscillator and feeds back the output to a reference double-delay frequency locking loop. The output end of a reference double-delay generator in the reference double-delay frequency locking loop is electrically connected with the input end of a sample-and-hold circuit, and the output end of the sample-and-hold circuit is electrically connected with the input end of an automatic phase error state detector. The sample-and-hold circuit simultaneously receives an oscillator output feedback signal of the sub-sampling phase-locked loop architecture. The output end of the automatic phase error state detector is electrically connected with the input end of an adaptive output frequency corrector, and the output end of the adaptive output frequency corrector is electrically connected with the sub-sampling phase-locked loop architecture. Unequal double-reference clock delays are introduced, the sample-and-hold circuit is combined to realize the detection of the output frequency, a new frequency locking loop working at a reference frequency is used to replace a traditional frequency locking loop, and the problem of high power consumption caused by a high-frequency frequency divider is solved.

The motor bearing wear monitoring device (5, 5A) monitors wear states of bearings (32, 33) with detection coils (C1 to C8). The device includes a storage (56, 56A) storing correspondence information on wear amount of the bearing and a voltage value corresponding to the wear amount, a wear amount detection unit detecting the wear amount of the bearing, based on differences between each of the detection coils (C1, C3) and between each of the detection coils (C5, C7), and a difference between a combined signal of the detection coils (C2, C4) and a combined signal of the detection coils (C6, C8); a signal generation unit (53, 553) generating an amplitude signal, based on the detection signal or the combined signal that are used for generating the difference; and a correction unit (551, 554) correcting the difference or the correspondence information depending on a driving frequency, based on the amplitude signal.

The invention relates to a system comprising a first and second generator (E1, E2) delivering excitation signals to a first and second resonator (R1, R2) generating chaotic signals. The resonators (R1, R2) are structurally different and coupled to one another. Advantageously, this system makes it possible to synchronize the chaotic signals and comprises: ● a dissipation correction module acting on the modulation frequencies fm1, fm2 of the excitation signals, ● a non-linearity correction module acting on the amplitudes of the excitation signals, ● a resonant frequency correction module acting on the carrier frequencies fc1, fc2 of the excitation signals, ● an amplitude correction module acting on the amplitudes of the chaotic signals. The invention also relates to a synchronization method based on this system.

The utility model relates to a unit used for radio frequency calibration, comprising an outer side support frame, two opposite ends of the outer side support frame are respectively plugged with a sealing end plate and an auxiliary end plate, and one side of the sealing end plate and one side of the auxiliary end plate are respectively provided with a sealing groove used for plugging and supporting. A plurality of inserting rods for positioning and supporting are arranged on the sealing end plate, and a plurality of connecting pins for connecting and supporting are uniformly arranged on the outer side of the outer side supporting frame. According to the radio frequency calibration unit, limiting support is provided for assembly and use of components in the frequency calibration unit based on support of the outer side support frames, the connection strength of the device during installation and use is improved through arrangement of the insertion rods, and the same outer side support frame can be adjusted to be square or square for use according to actual use requirements; and the device can be vertically or horizontally mounted and used, so that the device can be used in various forms and various connection states, and the use convenience of the device is improved.

The invention discloses a Hankel singular value decomposition-based magnetic resonance spectrum water peak modeling and post-processing method. The method comprises the following steps of: acquiring original multi-channel FID (Flame Ionization Detector) signals by a PRESS sequence; combining multi-channel signals, and performing frequency correction and eddy current correction; reconstructing and deducting a time domain water peak model, and executing exponential filtering processing; and performing baseline correction by adopting an asymmetric least square method to obtain a final spectrogram. Accurate modeling and removal of residual water peaks are realized by utilizing Hankel structure matrix singular value decomposition, adaptive baseline correction is performed by introducing an asymmetric least square method, interference of the residual water peaks is effectively reduced, the baseline smoothness of a spectrogram and the distinguishability of metabolic peaks are improved, and the method can be used for realizing accurate modeling and removal of the residual water peaks under the condition of not depending on additional modulation of a collection end or increasing of sequence complexity. The time domain signals are subjected to structured matrix decomposition to realize accurate modeling and removal of residual water peaks, the signal-to-noise ratio and metabolic peak resolution of the spectrogram are remarkably improved, the operation is stable, the robustness is high, and the obtained final MRS spectrogram can meet clinical requirements.

A method for operating a fast start-up oscillator system, which includes a reference oscillator and a quartz oscillator connected to an electronic oscillator circuit, which is provided to supply a master clock signal to a start-up controller configured to perform a fast start-up procedure of the quartz oscillator via the reference oscillator. The start-up controller includes a calculation unit and a memory unit for storing data in connection with the reference oscillator for starting the quartz oscillator. The method includes parameterising the calculation unit for starting the quartz oscillator, generating excitation bursts, determining a phase deviation in different successive periods between the oscillation of the reference oscillator and the oscillation of the quartz oscillator, calculating a frequency error in the calculation unit, and correcting the frequency of the reference oscillator to the frequency of the quartz oscillator.