High-frequency overtone TCXO based on mixing of dual crystal oscillators

To implement a high-stability and high-frequency overtone temperature-compensated crystal oscillator (TCXO) conveniently, an improved design of the novel overtone TCXO is described in this paper. A 120-MHz TCXO based on mixing of dual crystal oscillators is implemented. It utilizes a 100-MHz AT-cut 5th-overtone crystal oscillator mixed with a 20-MHz AT-cut voltage-controlled crystal oscillator (VCXO). The 120-MHz mixed product is filtered to produce the output signal. The total frequency deviation of 20-MHz and 100-MHz crystal oscillators is compensated by adjusting the output frequency of the 20-MHz oscillator to produce the stable 120-MHz output frequency. In this work, verifying experimental results of the compensation are presented. The stability of the experimental 120-MHz overtone TCXO with microprocessor temperature compensation achieves +/-2 X 10(-7) over the temperature range from -30 degrees C to +70 degrees C. A phase noise level of -133 dBc/Hz at 1 kHz offset has been initially measured for the prototype TCXO. The experimental result demonstrates this approach can conveniently implement the high-frequency overtone temperature compensation with a relatively high stability, and it is available for a wider frequency range as well.     

电磁悬浮转子的非线性控制

本文在对一个电磁悬浮转子实行线性控制研究的基础上,采用了两种非线性补偿控制,位移补偿和速度补偿。数字仿真结果表明,非线性补偿控制可使电磁悬浮转子达到更好的动态控制效果。     

电阻分流热电流温度补偿技术及应用

电阻分流热电流温度补偿技术及应用是为温度测量 热电偶与补偿导线失配专门研究一切后种新技术，试验与应用证明：它在补偿温度失配误差，减小测量系统的误差，校正起初炉温，改善系统温度响应特性方面都具有非常好的效果。     

Model-Based Compensation of SAR Nonlinearity

In the successive approximation analog-to-digital conversion principle, sample-and-hold (S/H) nonideality, producing an input signal variation that is less than the least significant bit (LSB) during the conversion time, gives rise to intrinsic and significant dynamic nonlinearity. In this paper, a method for compensating such nonlinearity is proposed. Theoretical fundamentals of the method are reported by paying particular attention to the accuracy of the compensation. With this aim, the dynamic phase distortion that is related to the intrinsic dynamic nonlinearity is modeled first. Then, a compensation technique based on the definition of compensated output levels maximizing the signal-to-noise-and-distortion (SINAD) ratio, namely, a particular case of the Max–Lloyd conditions for minimizing distortion in nonuniform quantizers, is applied. Simulation and experimental results show the method effectiveness in compensating the intrinsic dynamic nonlinearity and in incrementing the SINAD ratio in actual working conditions.      

Compensation of the bias caused by the wall filter on the mean Doppler frequency

In the presence of noise, any wall filter induces a bias on the mean Doppler frequency estimated by the algorithm based on the calculation of the phase of the autocorrelation function at lag 1. In this paper, it is shown that the bias results from the nonzero value of the autocorrelation function of the filtered noise at lag 1. A general method for compensating the bias was then deduced. It consists of a preliminary estimation of the filtered noise contribution and its subtraction from the autocorrelation function of the Doppler signal. The method is independent of the nature of the noise and wall filter. An evaluation of this method on simulated Doppler signals and on measurements from a moving-string phantom showed that effective compensation of the bias was obtained, but at the expense of a higher variance. Taking into account both the bias and the variance, however, it was shown that this method offers an improvement over the noncompensated method. Finally, the performance of this method was demonstrated using in vivo measurements taken from a human aorta.     

Analysis of the rutile-ring method of frequency-temperature compensating a high-Q whispering gallery sapphire resonator

The rutile-ring method of dielectrically frequency-temperature compensating a high-Q whispering gallery (WG) sapphire resonator is presented. Two and three-dimensional finite element (FE) analysis has been implemented to design and analyze the performance of such resonators, with excellent agreement between theory and experiment. A high-Q factor of 30 million at 13 GHz, and compensation temperature of 56 K was obtained. It is shown the frequency-temperature compensation can occur either because the rutile adds a small perturbation to the sapphire resonator or because of a mode interaction with a resonant mode in the rutile. The characteristics of both of these methods are described, and it is shown that for high frequency stability, it is best to compensate perturbatively     

Active and passive frequency stabilization for a Q-switched Z-fold radio-frequency-excited waveguide CO2 laser with two channels

We report on passive offset frequency stability in free-running applications and active offset frequency stability achieved by use of a frequency-locking technique for a Q-switched Z-fold rf-excited waveguide CO2 laser with two channels. The laser structure of common electrodes and two channels has the advantage of compensating for the frequency variation caused by variations in temperature, cavity length, gas refractive index, and mechanical vibrations, so its offset frequency stability is higher than that of two separate lasers. In the experiments, the offset frequency shift was less than 6 MHz for 3 min in free-running mode. The technique of active offset frequency locking by counting was also introduced. The beat frequency shifting value was smaller than +/- 0.5 MHz in the long-term.     

A novel microcomputer temperature-compensating method for an overtone crystal oscillator

In this paper, a novel microcomputer temperature-compensating method for an overtone crystal oscillator (MCOXO) is presented. In this method, a ceramic oscillator is chosen, and its output frequency is mixed with the output frequency of an overtone crystal oscillator. A crystal filter is used to suppress the spurious mixing products. A microcomputer is used to control the switch capacitance array that is connected to the ceramic oscillator circuit. The frequency deviation of the crystal oscillator is directly compensated by the output frequency of the ceramic oscillator. As a result, the method is able to overcome the disadvantages of frequency stability degradation and phase noise deterioration that are provoked by adding inductance or frequency multiplication in traditional compensating approaches. At the same time, this method is able to compensate a quite wide frequency range and many types of oscillators, not just crystal oscillators. The experimental compensating results show that, using this method, the frequency-temperature stability of a 100 MHz 5th overtone temperature-compensated crystal oscillator can achieve /spl les/ /spl plusmn/2/spl times/10/sup -6/ for 0-70/spl deg/C.     

薄膜热电偶的动态特性及动态补偿研究

针对用于瞬态高温测量薄膜热电偶的动态特性研究问题,本提出了为展宽其工作频带,以此来减小动态误差的方法。采用了一种脉冲激光法对薄膜热电偶进行了动态校准实验;利用基于沃尔什函数的建模方法建立了较好的薄膜热电偶动态模型;比一般的最小二乘法具有更高的拟合程度;通过地模型的极点和工作频带的分析,设计了动态补偿数字滤波器,改善薄膜热电偶的动态特性。     

减小噪声干扰的热敏电阻传感器动态测量误差补偿

为了补偿热敏电阻的动态测量误差，可在传感器的输出端串接一个动态补偿环节。该环节本质上是一个带通或高通滤波器，补偿环节的增加将引起严重的噪声放大，影响测量系统的精度。研究了在噪声环境下，改善热敏电阻传感器的动态特性的方法，该方法在采用实验数据得到补偿环节系数的同时，采用多项式预测滤波和中值滤波相结合的方法减小测量系统的噪声。仿真实验验证了该方法的有效性。     

Temperature feedback control for improving the stability of a semiconductor-metal-oxide (SMO) gas sensor

Stability is a major concern of semiconductor-metal-oxide (SMO) gas sensors in practical applications, as they may cause false alarm problems. Ambient temperature is a major factor affecting the SMO gas sensor's stability. In this paper, we use a novel way to improve temperature stability of SMO (tin oxide) gas sensors by applying a temperature feedback control circuits which are compatible with our microelectromechanical systems sensor fabrication. A built-in platinum temperature sensor can precisely detect the sensor's working temperature. It provides feedback information to compensate the microheater's current to maintain the sensor's working temperature constant, regardless of ambient temperature change. Test results showed that, with this approach, significant improvement of stability has been achieved compared to SMO gas sensors without temperature compensation under the same ambient variation. The algorithm is realized through a hardware circuit, whose advantages include real time, large feedback gain, and low cost.     

Cryogenic monolithic sapphire-rutile temperature compensated resonator oscillator

We have tested a new temperature-compensated sapphire resonator as frequency determining element for high-stability microwave oscillator. Temperature compensation has been obtained by coating the sapphire resonator with a thin rutile film. A 2-/spl mu/m rutile thickness is sufficient to reach turnover temperature higher than 40 K, and a 2/spl times/10/sup -12/ short-term frequency stability has been obtained.     

New method to build a high stability sapphire oscillator from the temperature compensation of the difference frequency between modes of orthogonal polarization

A new method to construct a high stability sapphire oscillator is presented. The method relies on the anisotropic fractional temperature coefficients of frequency (TCF) of orthogonally polarized modes. We show that it is possible to design a resonator with transverse electric and magnetic modes at different frequencies, but with the same TCF in units hertz per kelvin, resulting in temperature compensation of the difference frequency. Compensation was demonstrated between 50 to 77 K by measuring the difference frequency of two microwave oscillators frequency locked to orthogonally polarized whispering gallery modes. Curvature of the compensation points was measured to be 1 to 3 /spl times/ 10/sup -8/ K/sup -2/ between 50 and 77 K. This technique enables the construction of temperature compensated oscillators at any temperature and does not require dielectric, paramagnetic, or mechanical compensation techniques. Considering the above parameters, we show that it is possible to construct oscillators with fractional frequency instability at /spl tau/ = 1 s, of order 7.6 /spl times/ 10/sup -15/ at solid nitrogen temperature (/spl sim/50 K).     

Frequency-temperature compensation of piezoelectric resonators by electric DC bias field

Electromechanical resonators have been widely used in signal processing and frequency control applications. It has been found that the resonant frequency of most resonator devices is highly temperature dependent, as temperature variation leads to materials properties change as well as resonator dimension change, which result in the undesirable shift of the resonance frequency. In this paper, we present a new frequency tuning method in which direct current (DC) bias field is used to control the resonance frequency of the piezoelectric resonator that is subjected to ambient temperature variations. It has been found that, depending on the polarity, the application of a DC bias field can reduce or increase the resonance frequency of the resonator. The experimental results demonstrate that the DC bias field tuning can achieve fairly good temperature compensation within a certain temperature range, and that the mechanical Q factor of the resonator is quite stable under different DC bias fields.     

Temperature processing of an ultra stable quartz oscillator

Commonly, the required short-term frequency stability of an ultra stable quartz crystal oscillator (USXO) is a few parts in 10^-13 for averaging times of a few seconds. Moreover, the USXO must typically achieve a relative frequency variation of a few parts in 10 ^-10 over a temperature range from -30 to +70°C. Consequently, the USXO has to be ovenized. Basic data concerning the static and dynamic frequency versus temperature effects are first reviewed. These data allow one to evaluate how efficient the thermal regulator must be to achieve the aimed features in terms of temperature sensitivity. Usually the static thermal gain must reach at least 1000. A standard proportional-integral thermal controller, which can eliminate the static error, cannot afford doing this when fast thermal disturbances exist. Here, the thermal filtering must work in accordance with the cut-off frequency of the frequency-temperature transfer function of the quartz resonator. There exist various methods to control the oscillator temperature. The usual method consists of using more than one temperature-controlled-oven. This is often a volume-consuming process. An alternative approach, which is much simpler, is to add a slight compensation upon the feedback control system. Finally, a third way to improve the temperature regulation is based on a distribution of the monitored power. Obviously, a combination of those solutions is possible. Advantages and drawbacks of each of them are discussed in the paper. Practical results are shown and illustrated with 10-MHz USXOs     

基于FLANN算法的速度传感器动态补偿

磁电式速度传感器由于自身工作原理,其固有频率下限值受到结构和体积的限制.应用于振动测试时常需对其工作频带进行补偿扩展,以使其能检测固有频率以下的速度信号.本文针对磁电式速度传感器,建立了其动态数学模型,给出了一种基于函数链人工神经网络(FLANN)算法的动态补偿策略.分析对比了采用传感器输入输出设计的FLANN算法补偿器与采用零极点配置法进行动态补偿的效果.结果表明,采用FLANN算法设计的补偿器具有更小的补偿误差,且有效扩展了速度传感器的使用频带,很好地满足了工程上超低频振动测量的要求.     

Analysis of a negative impedance converter as a temperature compensator for bridge sensors

In this paper, we present an in-depth analysis of a negative impedance converter (NIC) as a temperature compensation device for bridge sensors. Even though its use has been proposed in some application notes and a patent, no theoretical justification has been reported so far, at least to the best of our knowledge. This paper attempts to fill this gap, giving closed-form expressions for a correct use of the NIC in any application. The influence of second-order effects in the temperature compensation is also considered. Experimental results are provided in order to verify the principles presented.     

考虑扣件温频变的车轨桥垂向耦合系统振动能量研究

通过对扣件进行定频变温试验,结合温频等效原理与高阶分数导数FVMP模型建立扣件的温频变动态力学模型,并在车-轨-桥耦合系统中采用新建模型模拟扣件,基于功率流法系统地分析与评价扣件温频变动态力学性能对车轨桥耦合系统振动能量分布与传递的影响.结果 表明:考虑扣件动参数频变会使中高频段内的轨道结构振动能量增大,对低频段的轨道...     

Fiber-optic temperature sensor used for oil well based on semiconductor optical absorption

This paper describes an optical-fiber sensor developed for temperature measurement under offshore oil well conditions. The sensor exploits the displacement of the optical absorption edge occurring in semiconductors under the influence of temperature variation as a result of temperature-induced energy shifting of conduction band extrema. The structure of the sensor and the measurement principle are described. The common-path reference measurement and node type error compensation technologies are developed. And, the detailed theoretical analysis indicates that the proposed sensor system can effectively improve measurement errors caused by light fluctuation, difference and variation of the detector responsiveness, circuit magnification times, and so on. It proves that this sensor system can be applied under long-term formidable conditions with fairly good measurement stability.     

Study on error calibration of fiber optic gyroscope under intense ambient temperature variation

A novel adaptive forward linear prediction (FLP) denoising algorithm and a temperature drift modeling and compensation concept based on ambient temperature change rate for fiber-optic gyroscope (FOG) are presented to calibrate the errors caused by intense ambient temperature variation. The intense ambient temperature variation will bring large temperature errors, which will degrade the performance of FOG. To analyze the temperature variation, characteristics of FOG temperature experiments are developed at first. Then the adaptive FLP denoising algorithm is employed to eliminate the noise aiming at reducing noise interference. After that, a simple modeling concept of building the compensation model between temperature drift and ambient temperature change rate is first to be given (we have not found a report of better results in any literature). The semiphysical simulation results show that the proposed method significantly reduces the noise and drift caused by intense ambient temperature variation.