An Improved 5 MHz Reference Oscillator for Time and Frequency Standard Applications

An improved 5 MHz reference oscillator for use in time and frequency standards has been developed. This oscillator, using an improved crystal unit, reaches a long term drift rate of less than 1×10-11 per day in a few days. The design includes precautions for reduction of effects of conducted electrical noise on the output frequency. Modular design of functional circuits provides ease of manufacture and uniformity of the product. Stabilized temperature control circuits have been utilized to provide improved oven performance. The oscillator has been tested for the effects on frequency and phase stability of power supply variation, changes in thermal environment, modulation by electrical noise, and mechanical vibration. Phase noise within the range of 100 Hz through 5.0 kHz varies from -120 dB to -125 dB.     

差分振子时间历程在微弱调制信号检测中的应用

单一的差分振子仅可实现对周期信号中某一频率成分进行检测,对于强噪声背景下的边频带,尽管可以利用多个差分振子组成差分阵列进行逐个检测,进而确定边频带的间隔,但这种做法无疑会带来巨大的计算量。在对调制信号进行Hilbert变换包络分析时,所得到的时域信号是原始调制信号中的低频分量,亦是调制波信号,若该低频分量仍然包含较强的噪声成分,传统的频谱分析将会失效。此时,我们可借助差分振子时间历程对含较强的噪声的包络进行检测。因此,提出基于差分振子时间历程的微弱调制信号检测方法,即首先对信号进行Hilbert包络解调,然后利用差分振子时间历程对含较强的噪声的幅值包络进行检测,并成功应用于风机早期故障检测中。     

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.     

Precision Clock and Time Transfer on a Wireless Telecommunication Link

Precise time dissemination is a key requirement for remote clock synchronization used in coordinated command of distributed actuators in various applications. We present a newly conceived low-cost clock system based on the time-to-digital converter (TDC) principle to generate, transfer, and compare time-coded sequences (TCSs) with nanosecond accuracy using a wireless telecommunication link. The clock principle counts pulse sequences with nanosecond precision derived from a low-frequency oven-controlled crystal oscillator (OCXO) stable frequency standard. The TCSs are transmitted to a remote transponder that distributes them to receiving stations, where the clock readings are processed. A simple short-range wireless telecommunication link was assembled to demonstrate the system. The repeated TCSs are received back and compared with the reference clock. We describe the clock, the telecommunication setup, and the electrical and electronic sources of delays. Comparison of mean TCSs taken every 0.629 s provided a time-domain midterm stability Allan deviation of about $1.3 times 10^{-11}$ at $tau = 10^{3} hbox{s}$. These results show the feasibility of a low-cost GPS-independent technique, exhibiting highly performing time-domain midterm stability. This system is a key requirement for a new proposed system for geopositioning.      

Is an oscillator-based measurement adequate in a liquid environment?

Oscillator-based measurements with quartz crystal resonators are analyzed. The investigations have shown that classical thickness monitors as well as many chemical vapor sensors based on a quartz crystal microbalance (QCM) work properly, even with simple oscillators. It was demonstrated that, for applications in a liquid environment, more sophisticated electronics are necessary. Also a comparison between the experimental results in liquids and the theoretical predictions is hardly possible without the knowledge of the oscillator behavior. As our solution, we present an automatic gain-controlled oscillator with two output signals, the oscillator frequency, and a signal that represents the damping of the quartz resonator. A calibration method is introduced, which allows one to calculate the series resonance frequency f/sub s/ and the series resistance R/sub s/ from these oscillator signals.     

HF and VHF Source Stabilization Technique Incorporating Q-Multiplied Quartz Crystal Resonator

A new approach is described for the desiga of HF/VHF crystal-controlled frequency sources exhibiting theoretical short-term stability unattainable through the use of conventional quartz oscillator design. The signal generator design uses the concept of AFC stabilization of a conventional quartz oscillator (VCXO) by means of a crystal-controlled highly selective active frequency reference. The AFC reference is a phase-shift type frequency discriminator that employs a product detector and an active Q-multiplied quartz crystal resonator. The extremely selective transmission response, large group delay, and power gain exhibited by the resonator, together with resonator phase noise levels comparable to that exhibited by the oscillator-maintaining circuit, provide the principal means for prediction of superior output signal spectral purity. Models of the resonators have been designed and constructed at 30 and 80 MHz, exhibiting 3-dB bandwidths of 30 and 160 Hz, respectively. Based on actual measurement of VHF Q-multiplied crystal resonator performance characteristics, approximately 16 dB improvement in VHF crystal-controlled frequency source spectral purity at low and moderate modulation rates is possible, compared to that attainable using the best available VHF quartz oscillator circuit designs.     

Oscillation of the center of the Rabi pedestal in an optically pumped Cs beam standard

This paper is devoted to the study of the symmetry of the Rabi pedestal of the clock transition in an optically pumped Cs beam frequency standard. The frequency of the microwave oscillator is locked on the center of the Rabi pedestal using a square wave frequency modulation. We observe a modulation of the center frequency as a function of the modulation depth. Experimental investigations on this unexpected effect are reported     

弹光调制器谐振特性研究及其谐振频率自跟踪

弹光调制器是一种由各向同性的弹光晶体和压电晶体组成的高品质因数热机电耦合器件,广泛用于偏振测量、光谱测量等诸多领域。但是在高压谐振状态下,其谐振频率会随着温度变化出现漂移,导致弹光调制器的相位调制幅值不稳定以及驱动效率降低。针对该问题,首先对弹光调制器谐振频率特性进行分析,建立了弹光调制器及其高压谐振驱动电路的复合谐振网络模型,提出了利用谐振网络的幅频特性进行频率跟踪的实现方法,并设计了基于现场可编程门阵列(field programmable gate array,FPGA)的控制测试系统,实现了谐振频率跟踪以及调制幅度的测量。通过测试验证了该方案可有效进行谐振频率跟踪,提高了弹光调制器的稳定性以及驱动效率,测试时长大于90 min,相位调制幅度的标准偏差为0.83% rad。

     

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.     

A new type of balanced-bridge controlled oscillator

A novel bridge-controlled crystal oscillator circuit with exceptional temperature stability is described. The contribution to the oscillator temperature coefficient of frequency (tempco) from the circuit components (exclusive of the crystal) is reduced to about 10(-11)/ degrees C, which is several orders of magnitude better than conventional oscillator circuits. This avoids a situation in which the overall tempco is limited by circuit component drift rather than crystal stability, which can easily occur with conventional circuits when the crystal is ovenized at a turnover point. Previous attempts to use a bridge in an oscillator were made by Meacham (1938), who used an imperfectly balanced bridge, and Sulzer (1955), who used a balanced pseudo-bridge. The reasons why these are unsatisfactory are discussed. Although the bridge greatly reduces reactive frequency pulling, it does not address directly the additional issue of pulling caused by variations in crystal drive current amplitude. However, it is an enabling technology for a novel ALC circuit with greatly improved stability. The new bridge-controlled oscillator is also much less sensitive to other environmental effects such as humidity (2x10 (-11), 5%/25% R.H. @70 degrees C), power supply voltage, load impedance, and stray capacitance.     

Detecting synchronization of self-sustained oscillators using wavelet analysis of univariate data for variable external drive frequency

A new method based on the continuous wavelet transform of univariate data is proposed for detecting the synchronization of a self-sustained oscillator under external drive action with linear frequency modulation. The efficacy of the proposed method is demonstrated in application to a model van der Pol oscillator and experimental physiological data.     

Special Purpose Ammonia Frequency Standard a Feasibility Study

We have investigated the feasibility of a special purpose frequency standard based on microwave absorption in ammonia gas (N15H3). Such a device would potentially fill a need in certain communications and navigation applications for an oscillator which has medium stability, greater accuracy (~10-9) than that provided by crystal oscillators, but a cost significantly smaller than that of more sophisticated atomic frequency standards. A device was constructed using a stripline oscillator near 0.5 GHz whose multiplied output was frequency-locked to the absorption of the 3-3 line in N15H3 (~22.8 GHz). Output between 5 and 10 MHz was provided by direct division from the 0.5-GHz oscillator. Observed stability was 2 x 10-10 from 10 to 6000 s, and reproducibility (accuracy) is estimated to be ±2 x 10-9. The unique features of this device, which include 1) high-performance stripline oscillator, 2) digital servo techniques, 3) unique oscillator-cavity servo, 4) pressure shift compensation scheme, and 5) acceleration insensitivity, are discussed. Areas for further study are noted.     

石英晶体振荡器加速度效应及敏感度的测试

石英晶体振荡器因其具有频率稳定度高的特点,作为标准频率源或脉冲信号源提供频率基准是目前其它类型的振荡器所不能替代的.而加速度对晶振输出频率影响的补偿问题目前还没有得到很好解决,加速度已成为当前影响晶体振荡器准确度的重要因素.本文简要介绍了加速度对晶体频率的影响,国内外加速度敏感度的测试方法及其改进方法,并以实验验证,取得了较好的效果.     

Long-term frequency aging for unpowered space-class oscillators

Very little data exists regarding the long-term aging performance of space-rated oscillators in the non-operating mode. This paper provides empirical evidence that may be used to estimate the performance of unpowered oscillators for long-term space missions, as well as an aid in validating the worst-case analyses that are routinely performed on these oscillators. The proper operation of any space vehicle is dependent on the performance of the onboard master oscillator. For maximum reliability, the onboard clock is often provided as a dualor triple-redundant ensemble, with one active oscillator. The backup oscillator(s) are usually powered off and may be off for a significant percentage of the mission. A significant parameter of importance for oscillator performance is the aging rate. Papers have been presented on the aging performance of active oscillators in space, but very little data exists regarding the long-term aging performance of oscillators in the nonoperating mode. The aging rate data are extremely important for predicting the expected performance of these backup oscillators after 10 or 15 years in of non-operation in space. This paper presents performance data derived from temperature controlled crystal oscillators and oven controlled crystal oscillators that have been dormant for decades.     

Theory of Hydrogen-Maser Auto-Tuning Systems Based on the Frequency or the Phase Method

A theoretical analysis of auto-tuning systems for actively operated hydrogen (H) masers is presented. Tuning procedures based on changes in the frequency or the phase of oscillation are considered and compared. The analysis takes into account the basic results of sampling theory. The condition which should be satisfied when the reference frequency source is perturbed by white or flicker phase noise is specified. It is shown that the phase method should give better results than the frequency method when the reference source is a good quartz crystal oscillator.     

Reducing local oscillator phase noise limitations on the frequencystability of passive frequency standards: tests of a new concept

We report on the experimental test of a new concept for reducing the limitation on short-term frequency stability of passive frequency standards due to local oscillator phase noise. This concept is general and can be applied to many passive frequency standards. Systems that use sinewave modulation to interrogate a stable resonance are limited in short-term frequency stability by phase noise at the second harmonic of the modulation, f_m. This effect limits the fractional frequency stability to approximately σ_v(τ7)=0.9(f _m/ν₀) (S_φ(2f_m))^1/2τ^-1/2, where ν₀ is the carrier frequency and S_φ(2f _m) is the phase noise at twice the modulation frequency. (Contributions from higher even harmonics of the modulation generally can be neglected). This new concept uses notch filters at ±2f_m from the carrier to reduce this effect. Tests on a modified passive rubidium standard demonstrate an improvement of approximately 18 in σ_y(τ). The dual notch filters proved to be feasible and were obtained commercially. Measurements suggest that ultimate performances of less than 2×10^-14τ^-1/2 are possible if the atomic resonance has sufficient quality     

Expected quality factor of a simple tuned oscillator

A positive feedback system oscillating under self-sustained mode is shown to have an extremely high gain. Modeled as one port, the expected Q is much higher than the loaded Q-factor of the resonator. With just thermal noise present, random phase/frequency deviation is linear. Centered about the oscillator frequency omega/(0), noise frequency on both sides is more amplified with decreasing separation distance. Ultimately, frequency pulling may result in synchronous locking with hysteresis, which occurs because a real oscillator displays a truncated limiting curve. Once locked onto a signal, smaller levels are ignored. A new approach to the design and characterization of a simple tuned oscillator is offered: According to the phenomenon of injection locking, there exists an expected quality factor relating the shape of the truncated limiting curve to an ideal curve. In this paper, synthesis and innovative analytical methods of academic interest are revealed: 1) application of the transducer loss method is revised to establish a new method for oscillator characterization; 2) a transparent method of normalizing a two-port network in the presence of white noise is developed; and 3) in quartz crystal controlled oscillators, characterization of the noise originating from an equivalent noise-resistance determined from parameter of the quartz crystal is proposed. It is shown that the two-port model can also be approximated on a one-port basis. In conclusion, a sample of closed-form estimation of expected Q-factor order of magnitude of piezoelectric resonator oscillators is calculated.     

基于性能可调阶梯型变幅杆的超声波振子调谐研究

为减小超声波振子外接负载时其谐振频率漂移的幅度,使用机电等效电路法和COMSOL Multiphysics 5.3有限元仿真软件设计制造了一种基于性能可调阶梯型变幅杆的超声波振子。对该超声波振子的谐振频率进行有限元仿真和现场测试。以超声清洗机为例,搭建与其原理相似的试验装置,以不同液面高度的水作为变幅杆的外接负载,探究在不同外接负载情况下,调节连接在变幅杆处压电晶堆的调谐电感对解决超声波振子谐振频率漂移问题的有效性。试验结果表明：随着水杯中液面高度的增加,超声波振子的谐振频率整体呈上升趋势;通过在变幅杆的压电晶堆处外接调谐电感,超声波振子的谐振频率会得到一定的补偿,可重新回归到原始设定的谐振频率值附近。研究表明在使用超声波振子进行超声辅助加工时,该超声波振子对减小外接负载引起的谐振频率漂移幅度具有一定作用。研究结果可为超声波振子的调谐提供新思路和新方法。     

The implementation of a digital sine wave oscillator using theTMS320C25: distortion reduction and applications

The implementation of a digital sine wave oscillator using the TMS320C25 digital signal processor (DSP) is described. The system is implemented with the Dalanco Spry model 25 DSP board, and a software system is designed whereby an IBM PC host computer provides control of the waveform generator functions and parameters. Waveforms are generated using the lookup-table (LUT) method. The methods of direct LUT and linear interpolation of missing samples are implemented and compared with a method that uses a trigonometric identity to reduce the harmonic distortion of the sine wave by effectively increasing the table length of the direct LUT method. The results of an experiment performed in the digital domain are presented without consideration of the problem of analog reconstruction. The oscillator can produce a sine wave without the nonuniform sampling distortion associated with fractional addressing, over the range of 7.2 Hz to 58.8 kHz, with a resolution of 7.2 Hz using 384 data words. The trigonometric identity method uses less data memory than other methods for the same distortion levels. Waveforms for the sum of two sine waves, a frequency swept sine wave, amplitude modulation (AM), and frequency modulation (FM) signals are shown as applications of the waveform generator     

OCXO design using composite-heating of the crystal resonator

The design of a composite-heated quartz crystal resonator for OCXO applications is described. A mathematical model of the transient processes in the device is presented and is used to identify the physical and electrical parameters of the resonator providing optimized warm-up time, frequency stability, and power consumption. A prototype resonator exhibiting a warm-up time of 15 s, frequency versus temperature stability better than 3×10^-8, and heating current of about 5 mA is described