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.

Mobile Rayleigh Doppler wind lidar based on double-edge technique

Abstract: We describe a mobile molecular Doppler wind lidar (DWL) based on double-edge technique for wind measurement of altitudes ranging from 10 to 40 km. A triple Fabry-Perot etalon is employed as a frequency discriminator to determine the Doppler shift proportional to the wind velocity. The lidar operates at 355 nm with a 45-cm-aperture telescope and a matching azimuth-over-elevation scanner that provides full hemispherical pointing. To guarantee wind accuracy, a single servo loop is used to monitor the outgoing laser frequency to remove inaccuracies due to the frequency drift of the laser or the etalon. The standard deviation of the outgoing laser frequency drift is 6.18 MHz and the corresponding velocity error is 1.11 m/s. The wind profiles measured by the DWL are in good agreement with the results of the wind profile radar (WPR). Evaluation is achieved by comparing at altitudes from 2 to 8 km. The relative error of horizontal wind speed is from 0.8 to 1.8 m/s in the compared ranges. The wind accuracy is less than 6 m/s at 40 km and 3 m/s at 10 km.

Oscillator circuit for a semiconductor memory having a temperature dependent cycle

Abstract: An oscilator circuit for a integrated circuit memory device to optimize the refresh operating circuit and suppress wasteful power consumption in which the oscillator frequency is set high during high temperatures and the oscillator frequency is set low during low temperatures. A current I 1 is generated by means of the current source 100 a having characteristics in which it is increased during high temperatures and decreased during low temperatures, and is supplied to the ring oscillator 200 . A current corresponding to the current I 1 is supplied to each inverter in the frame oscillator 200 , and since the oscillator frequency is controlled by means of the current value of the supplied current, the frequency of the clock signal CLK generated increases accompanying a rise in temperature, and since the refresh operation is conducted based on the clock signal CLK, the data holding capabilities can be ensured during high temperatures, wasteful power consumption can be reduced during low temperatures, and optimization of the refresh operating frequency can be realized.

Extending the frequency range of a Wien-bridge oscillator using composite operational amplifiers

Abstract: The author describes the use of composite operational amplifiers to extend the useful operating frequency range of an operational amplifier-based Wien-bridge oscillator The effect of the finite gain-bandwidth product (GB) of the operational amplifier (OA) is analyzed This analysis shows that for a certain GB the frequency of oscillation is less than the theoretical value and that the error increases with frequency A composite OA is then used to decrease the errors due to GB This is verified theoretically and experimentally Although the composite OA improves the frequency performance of the oscillator, the amplitude of the output decreases with frequency An automatic-gain control circuit is incorporated to keep an output amplitude constant over the useful frequency range Distortion measurements are presented >

Phase locked loop frequency synthesizer where frequency gain variation controlled oscillator is compensated

Abstract: A phase locked loop frequency synthesizer in which frequency gain of a voltage controlled oscillator is compensated is disclosed. The phase locked loop frequency synthesizer measures a frequency gain variation of the voltage controlled oscillator and compensates the variation by controlling phase gain of a phase comparator or voltage gain of a loop filter. Gain characteristics of the voltage controlled oscillator are detected and fed back to control frequency gain of the voltage controlled oscillator, so as to allow the voltage controlled oscillator to have uniform frequency gain. Accordingly, the phase locked loop frequency synthesizer can obtain uniform loop gain irrespective of a frequency gain variation of the voltage controlled oscillator and provide optimum phase noise characteristics and stability.

Method for carrier frequency recovery and optical intradyne coherent receiver

Abstract: A method for carrier frequency recovery in an optical coherent transmission system is provided in which at least one kind of equalization of a received signal is performed in frequency domain, the method comprising: performing a frequency offset compensation in frequency domain on a received signal according to an estimated value of the frequency offset; obtaining the signal with the frequency offset compensated. Further, an optical coherent receiver is provided comprising: an equalization unit, adapted to perform at least one kind of optical distortion compensation of a received signal in frequency domain; a frequency offset compensation unit, adapted to perform the frequency offset compensation in frequency domain on a received signal according to an estimated value of the frequency offset to obtain the signal with frequency offset compensated. The method and the receiver provided by the present invention in carrier frequency recovery need only a frequency shift of the signal spectrum, reducing the computation complexity dramatically thus the processing is speed up and the resources needed are very much saved.