Showing papers on "Crystal oven published in 1988"

Method for temperature compensation of a voltage-controlled crystal oscillator in a phase control circuit

Abstract: A heating or, respectively, cooling device is realized by a Peltier element and is assigned to a crystal oscillator and driven by a processor with the assistance of a temperature sensor such that the crystal exhibits one of two selected temperatures lying closest to the ambient temperature. A compensation value is stored in the memory of the processor for each of the crystal temperatures selected from an operating temperature range. This compensation value effects the compensation of the frequency deviations of the crystal oscillator that are caused by temperature fluctuations.

Apparatus and method for detecting small changes in attached mass of piezoelectric devices used as sensors

Abstract: In analysis, particularly for medical diagnostics, material can be selectively bound to the surface of a piezoelectric crystal by a reagent. The amount of material so bound affects the speed of propagation of an acoustic wave launched and received on the crystal surface by respective electrode pairs. Previously the crystal was used as a resonant element in an oscillator controlling the frequency of oscillation and so indicating the amount of bound material. However, the oscillator was either unstable or the range of bound masses too small to be of practical use. In the present invention delay between launch and reception of the acoustic wave provides a control signal for a voltage controlled oscillator. A much more stable system can therefore be constructed with a wide working range and high stability since the crystal is no longer the resonant element. Much greater sensitivity is also possible since the oscillator frequency may be greatly increased. A control signal representative of delay may be produced by a phase comparator comparing the phase of two input signals: one direct from the oscillator, and one from the reception of an acoustic wave on the crystal surface launched using a signal from the oscillator. The signal to the crystal may be modulated using a low frequency oscillator before it reaches the crystal to aid the oscillator in following frequency changes due to changing crystal surface conditions and the resulting signal may be summed with the output of a resonance oscillator before application to the crystal to aid the oscillator in initially settling to a stable frequency.

The influence of pressure and humidity on the medium and long-term frequency stability of quartz oscillators

Abstract: It is shown that the medium-term frequency stability of four different 5-MHz oscillators controlled by two different types of AT-cut resonators is sensitive to changes in atmospheric moisture and possibly pressure. Stabilizing the pressure and humidity, in addition to the normal parameters in an otherwise controlled laboratory setting, improves the frequency stability for measurement times in the region of hours to days. The mechanism by which fluctuations in moisture and possibly pressure bring about frequency changes is speculated upon, noting that the effect could be due to changes in the thermal gradients, changes in the dielectric constants, or residual leakage between critical circuit elements. A simple test is introduced to determine the relative importance of thermal gradients within air-enclosed ovens. >

Design and implementation of a CMOS VCXO for FM stereo decoders

Abstract: A circuit technique to simulate large variable capacitance of both positive and negative polarities over a given frequency range is discussed The simulated capacitance can be varied by voltage control from -60 to +100 pF The capacitor-simulating circuit is connected in parallel with a resonator to tune its parallel resonance An oscillator with grounded resonator is also developed Together with the variable capacitor, a voltage-controlled crystal oscillator (VCXO) is realized The oscillation frequency of the oscillator can be tuned continuously from 452 to 461 kHz by voltage control Detailed analyses to completely characterize the oscillator with a simple expression are presented The prototype of the VCXO has been fabricated in a 4- mu m standard CMOS process >

Crystal oscillators using negative voltage gain, single pole response amplifiers

Abstract: A simple and inexpensive crystal oscillator is provided which employs negative voltage gain, single pole response amplifiers. The amplifiers may include such configurations as gate inverters, operational amplifiers and conventional bipolar transistor amplifiers, all of which operate at a frequency which is on the roll-off portion of their gain versus frequency curve. Several amplifier feedback circuit variations are employed to set desired bias levels and to allow the oscillator to operate at the crystal's fundamental frequency or at an overtone of the fundamental frequency. The oscillator is made less expensive than comparable oscillators by employing relatively low frequency amplifiers and operating them at roll-off, at frequencies beyond which they are customarily used. Simplicity is provided because operation at roll-off eliminates components ordinarily required in similar circuits to provide sufficient phase-shift in the feedback circuitry for oscillation to occur.

Oscillator, in particular a surface acoustic wave oscillator, frequency controlled by controlling its temperature

Abstract: An oscillator is provided, in particular a surface acoustic wave oscillator, frequency controlled by controlling its temperature, which oscillator comprises a SAW resonator frequency controlled by an integral loop including a heating means coupled thermally to the resonator and by two electric respectively proportional and semi-integral loops.

Standard frequency clock generator

Abstract: PURPOSE: To always generate a clock signal of high precision by switching one of a highly stable oscillator like a cesium oscillator and quartz oscillators subordinate to this oscillator to another at the time of the occurrence of trouble in the output of one of these oscillators. CONSTITUTION: Changeover switches 14 and 15 are inserted between two quartz oscillators 12 and 13 as subordinate oscillators and synthesizers 16 and 17 to always monitor relations between outputs of a cesium oscillator 11 and quartz oscillators 12 and 13. When trouble occurs in quartz oscillators 12 and 13, signals of these oscillators are switched to the signal of the cesium oscillator 11 and this signal is supplied to synthesizers 16 and 17. Thus, the clock signal high in precision is always generated. COPYRIGHT: (C)1990,JPO&Japio

Method for the temperature compensation of a voltage-controlled quartz oscillator in a phase-locked loop

Abstract: The crystal oscillator is associated with a heating or cooling device which can be implemented as Peltier element and is driven by a processor device (PZE) with the aid of a temperature measuring device (TS), in such a manner that the crystal exhibits one of two selected temperatures closest to the ambient temperature. For each of the crystal temperatures selected from an operating temperature range, a compensation value is stored in a memory of the processor device (PZE). This compensation value compensates for the frequency deviations of the crystal oscillator which are caused by temperature fluctuations. … …

Method of making a crystal oscillator desensitized to accelerationfields

Abstract: An oscillator and a resonator included in the oscillator are operated at arequency that is not the resonator frequency but that is off resonance at a frequency where the resonator has a minimum acceleration sensitivity and the desired oscillator output frequency is then electronically produced using electronic frequency synthesis techniques.

A novel compact rubidium frequency standard with a low sensitivity to magnetic and vibrational disturbances

Abstract: A rubidium frequency standard with a compact and ruggedized design is developed. Two improvements are incorporated into the traditional design: an electronic method which improves the frequency stability under vibration and accelerations, and an electronic method to eliminate the sensitivity to magnetic fields. These schemes are incorporated into present rubidium frequency standard. This unit has a very high modularity using partially hybridized circuits. It has a good short-term stability between 1 and 500 s. The OCXO incorporates a low-g-sensitivity SC-cut quartz crystal. >

Method of measuring the thermal hysteresis of quartz crystal resonators

Abstract: The thermal hysteresis of quartz crystal resonators is measured by exciting two modes of a quartz crystal of interest with an external frequency source at a preselected temperature, calculating the difference frequency as between the modes, resetting to the original set temperature after temporarily altering the temperature, remeasuring the frequencies while maintaining the temperature and the difference frequency at the same respective values as the original values, and taking the mode frequency difference as representative of the thermal hysteresis of the crystal.

Frequency stability of emitter follower type crystal oscillators

Abstract: Recently, crystal oscillators are used increasingly with the advances of electronic components. Particularly, the adjustmentfree crystal oscillators with only a few circuit elements are used widely since they are suited for IC's. Hence, stabilization of their frequency is very important. In this paper, the simplest emitter follower type crystal oscillator made of a transistor, a quartz crystal, a capacitor, and three resistors is studied in terms of its frequency stability. From the calculations and experiments, the following results have been obtained. The oscillation frequency is more stable against the change of an external capacitance if larger values are chosen for the collector capacitance CC, the grounded base current gain α, and the α cutoff frequency fα. Against the change of the power supply voltage, the optimum value of fα can be determined after CC is selected from the forementioned condition. The oscillation frequency deviation is smaller for a larger equivalent inductance L1 regardless of the Q value of the crystal. Based on these results, it is found that the improvement is more than sixfold against the variation of the power supply voltage, and more than elevenfold against that of the circuit capacitance.

Temperature and angular variations of piezoelectric coupling in quartz

Abstract: Measurements of resonance frequency versus temperature have been made on many accurately characterized quartz vibrators as part of an effort to obtain a highly precise set of material parameters to replace the most widely used set, which is now 25 years old. Preliminary data are presented for the first temperature derivative of piezoelectric coupling as a function of orientation angle. These numbers permit prediction of temperature coefficient change as a function of location on the impedance circle and are important for temperature-compensated crystal oscillator (TCXO) applications. >

The relaxation quartz crystal oscillators-design and performances

Abstract: Rules are described for analysis and design of relaxation quartz crystal oscillators. Two based topologies for relaxation oscillators and the corresponding mathematical model describing their behavior are presented. Using a phase-space approach the oscillating condition and frequency and the flicker frequency noise level are calculated. The characteristics of an optimal oscillator circuit having a loaded crystal Q-factor close to the unloaded one are determined. Based on the analysis, the design rules for an optimal relaxation circuit are derived. The rules are demonstrated through the design and realization of an optimal relaxation crystal oscillator based on two-transistor negative resistance two-ports. The measured characteristics of the realized oscillator are presented and compared to those of known relaxation circuits. It is concluded that the optimal relaxation crystal oscillator consists of a small number of component circuits having low phase noise and small sensitivity to circuit and ambient parameter variations. >

Automatically self-calibrating oscillators in heterodyned radio receivers

Abstract: There is provided a system for automatically integrally calibrating an oscillator (10) and/or a phase-locked loop (30, 32, 34) to achieve frequency accuracy and stability in a synthesized radio, particularly a radio where the temperature of an oscillator can be set. Temperature calibration is performed by integrally determining the present optimal operating temperature for the oscillator and integrally resetting the temperature of the oscillator to that optimal temperature. Thus, frequency vs. temperature stability is achieved; frequency calibration may follow.

Optically Powered Sensors Based On Resonant Structures : Mathematical Analysis

Abstract: Optically powered resonant structures are important in passive sensor systems which rely upon the use of fibre optics for excitation and interrogation. In this study, photothermal excitaion of the device was simulated and comparison of the output characteristics obtained was made with the work of the experimental investigations. 1. INTRODUCTION(a) General IntroductionIntensive research work over the last several years has resulted in the publication of many schemes for the sensing of important physical and chemical parameters by optical means, using fibre optic systems. Such work has been reviewed by a number of authors [1-13,19] and as the technology has begun to mature, the directions for future research are becoming more clear, e.g., considerable interest has been shown in systems which do provide an output in a non-analogue form. The piezoelectric quartz resonator has been used as a frequency standard for many years and the frequency sensitivity to strain/stress in quartz oscillators has been used as the basis of a number of conventional sensors, for force and presssure measurement in particular. Quartz has a high 'Q' factor, is readily available due to its use in conventional sensors and in addition it has good optical properties. It is very stable, can sustain both compressive and tensile stresses and has a low ageing rate. Quartz crystal resonators have the potential to be used in any sensor scheme where the parameter to be measured can be converted to a stress effect in the crystal and thus to a corresponding resonant frequency change. As a result, there is a need to investigate these devices fully to extract their potential for optical sensor applications, to benefit from their digital form of (frequency) information output.(b) RequirementsA study of the literature has shown that some authors [6,7,8] have emphasized, in their anlayses, the obtaining of the resonant frequency and mode shapes of simple structures in quartz based sensors for different uses. In this paper, the more detailed analytical techniques recently made available (including the use of the finite element method) are implemented to model an optically driven quartz crystal plate, typical of that used in the fibre optic sensor schemes discussed previously by some of the authors [2,9,10], to yield a fuller assessment of various physical aspects of a prototype sensor scheme. In such an analysis, it is considered important to use a practical and experimentally demonstrated example as the basis of the verification of the model and thus make comparisons with actual results from an experiment. Additionally, the modelling is not limited only to one material, such as quartz, and the characteristics of other important resonant sensor materials eg. silicon [19] could equally be predicted. Thus this leads to the development of a valuable tool for the sensor designer.2. PHYSICAL DESIGN CONSIDERATIONS(a) Theoretical Background - Elementary ConsiderationsIn this modelling exercise the sensors of interest are those based on a vibrating quartz crystal executing a flexural mode of vibration [4,9,12]. A schematic diagram of the crystal to be modelled and typical of such sensor elements is shown in Figure 1. Dimensions used are those of McGlade et al and Mallalieu [4,13], where available, which are similar to the sensor element size in the work of Grattan et al [10]. It is assumed that the quartz crystal is clamped at both ends and it is driven optically by light from an input fibre. Thus the quartz crystal vibrates due to the photothermal effect [9], as it is coated with a thin layer of a material which absorbs the incident optical power. The material is chosen to be absorbant at a near infrared wavelength of the light source (most conveniently a LED ) causing the resonance in the crystal , where the modulation frequency is the resonant frequency of the quartz crystal. The absorption of the light over the period that the source is energized heats the crystal and thus an a.c. stress component is applied hi addition to the d.c. stress which is present due to the axial load generated by the parameter to be measured. Usually the latter effect is enhanced by the special mechanical support used which is for