Frequency drift

About: Frequency drift is a research topic. Over the lifetime, 5054 publications have been published within this topic receiving 56191 citations. The topic is also known as: chirp rate.

Digital temperature-compensated oscillator

Abstract: A digital temperature-compensated oscillator comprises a crystal oscillator, a first memory previously storing digital temperature compensation data obtained by previously measuring the relation between the ambient temperatures and the frequency deviations of the crystal oscillator, a second memory for storing frequency offset amounts of the oscillation frequency of the crystal oscillator, a temperature sensor for outputting analog detection data relating to the ambient temperature, an A/D converter for converting the analog detection data to digital detection data, a readout circuit for reading out temperature compensation data corresponding to the digital detection data and stored in the first memory according to the digital detection data and reading out the frequency offset amount stored in the second memory according to the digital detection data, an operation circuit for effecting the following calculation by use of the readout temperature compensation data and readout frequency offset amount to derive digital control voltage, V.sub.c =V.sub.co +(K.sub.00 +V.sub.co K.sub.10 +K.sub.01 T)×(ΔF+ΔF 2 ×K 10 /2) where K 00 , K 01 and K 10 are constants, V co is an initial value of the control voltage, T is an ambient temperature and ΔF is a frequency offset amount, a D/A converter for converting the digital control voltage into an analog control voltage, and a voltage-capacitance converter for receiving the analog control voltage and generating a control signal to be supplied to the crystal oscillator according to the received analog control voltage, wherein the frequency of the crystal oscillator is controlled according to the control signal.

Sandia frequency shift parameter selection for multi-inverter systems to eliminate non-detection zone

Abstract: Among frequency drift islanding detection methods, Sandia frequency shift (SFS) is considered as one of the most effective methods in detecting islanding conditions for grid connected photovoltaic (PV) inverters. The performance of the SFS method during an islanding condition and its non-detection zone (NDZ) depends to a great extent on its parameters. Furthermore, the capability of the SFS method to detect an islanding condition deteriorates with multiple PV inverters. A mathematical formula is derived to aid protection engineers in determining the optimal setting of the SFS islanding detection parameters with multiple inverter-based distributed generation (DG), such as PV systems, to eliminate the NDZ. The derived formula is applied to multiple DG systems equipped with the over frequency/under frequency protection, active frequency drift and SFS islanding detection methods and is verified through NDZ analysis and simulation results on PSCAD/EMTDC. The derived formula provides an effective guideline for designing frequency drift methods in multi-inverter-based DG systems.

Joint phase/amplitude estimation and symbol detection for wireless ICI self-cancellation coded OFDM systems

Abstract: OFDM has been applied in the current wireless local-area networks and digital video broadcasting systems since it has the advantage over the conventional single-carrier modulation schemes when the frequency-selective fadings are present. Nevertheless, intercarrier-interference (ICI) due to Doppler frequency drift, phase offset, local oscillator frequency drift, and multipath fading will be a severe problem in OFDM systems. Previous ICI self-cancellation coding schemes can greatly reduce the ICI, but they are very sensitive to the phase ambiguity, which is due to the composite effect of the phase offset, the multipath fading and the local frequency drift. In this paper, the phase ambiguity and amplitude ambiguity problems in ICI self-cancellation coded OFDM receivers will be formulated and discussed. Then, a novel receiver which combines the current ICI self-cancellation coding techniques with a new expectation-maximization-based joint phase/amplitude estimation and symbol detection scheme is proposed. The outstanding performance of this proposed scheme is shown and compared with other existing methods at different noise levels through OFDM simulations.

Digital radio frequency compensation

Abstract: A frequency compensation voltage system in a mobile station of a digital packet radio system is used to modify the output frequency of the mobile's crystal controlled reference oscillator. A burst transmitted by a base station is received by the mobile and, once it is determined that the burst came from the correct base station, the frequency of the burst is compared to that of the reference oscillator. Stored voltage values corresponding to temperature, aging and tuning voltage compensation values are modified to conform the frequency of the mobile's reference oscillator to that of the burst received from the base station.

Wide frequency range CMOS relaxation oscillator with variable hysteresis

Abstract: A voltage controlled oscillator (VCO) which may be adjusted to provide oscillatory signals for a wide range of frequencies includes a relaxation oscillator in which a ramp signal is compared to a reference threshold which exhibits hysteresis. The frequency of the oscillator is changed by varying the hysteresis range of the threshold level and by changing the rate at which the ramp is generated. At higher frequencies, the signal processing delay through the comparator is a factor in determining the frequency of the signal produced by the oscillator. Current sources internal to the oscillator are controlled by a reference potential that is generated from an externally supplied band-gap reference potential. The VCO is used in a phase-locked loop which includes a charge pump circuit that accumulates charge on a capacitor responsive to limited-width pulses applied to a current source which is controlled by the reference potential generated in the VCO.