Showing papers on "Crystal oven published in 1995"

Method of making an oven controlled crystal oscillator the frequency of which remains ultrastable under temperature variations

Abstract: The present invention provides for methods of increasing the frequency vs temperature ("f vs T") stability of Oven Controlled Crystal Oscillators to levels which are superior to atomic frequency standards and 100 to 10,000 times higher than that currently available from the best crystal oscillators This method encompasses the steps of making an SC-cut quartz resonator with upper and lower turnover temperatures at or near the resonator's inflection temperature, inserting the resonator into a high-stability oscillator circuit, placing the circuit into a high-stability, high thermal gain oven and adjusting the oven temperature to a set-point at or near one of the resonator's turnover temperatures A preferred embodiment of the method of the present invention is also disclosed which comprises forming an SC-cut quartz resonator with upper and lower turnover temperatures within 10 K of the resonator's inflection temperature, inserting the resonator into a dual-mode high-stability oscillator circuit which is placed in an oven having a thermal gain exceeding 5,000 and temperature fluctuations smaller than 50 mK and utilizing a thermometric beat frequency of said resonator to adjust the oven temperature to a set-point within 100 mK of the lower turnover temperature

Fast start-up crystal oscillator circuits

Abstract: This paper presents a reduction method of the start-up time after the switch-on of the D.C. power supply of a crystal oscillator circuit. It is shown that a fast start-up crystal oscillator can easily be obtained by changing only the circuit connection of the crystal resonator. The new scheme can be applied to the usual Colpitts crystal oscillator circuits, to the cascode crystal oscillator circuits, and also to the overtone crystal oscillator circuits.

Multiple crystal non-linear frequency conversion apparatus

Abstract: A non-linear frequency conversion device is tunable over a wide tuning range. An input source provides a first input beam with a frequency μl. A first frequency conversion crystal has an input beam face that is cut at a phase matching angle υ1 and is positioned on a first stage at a stage angle α1. The first frequency conversion crystal provides frequency conversion of the input beam of frequency μ1 to a selected frequency μ2 of a first portion of the selected tuning range. A second frequency conversion crystal has an input beam face that is cut at a phase matching angle υ2 and is positioned on a second stage at a stage angle α2. The second frequency conversion crystal provides frequency conversion of the input beam from a frequency μ1 to a selected frequency μ3 of a second portion of the selected tuning range. Only one of the frequency conversion crystals provides frequency conversion in the range for a particular input wavelength while the other crystal is inactive, and serves as a beam displacement compensator. The non-linear frequency conversion device can be used for second harmonic generation, sum frequency mixing, difference frequency mixing, or optical parametric generation.

Temperature stable crystal oscillator

Abstract: A crystal oscillator is proposed which can exhibit a frequency versus temperature stability comparable to that of the best atomic frequency standards. >

New digital compensation technique for the design of a microcomputer compensated crystal oscillator

Abstract: The study of the stability of frequency sources is a matter of major interest due to the evolution of communication and instrumentation systems resulting in increasing the number of channels in a limited spectrum, and reducing size and power consumption. The paper relates laboratory experiences that explain the behavior versus temperature of thickness-mode quartz crystal resonators (AT- and SC-cut crystals) that are applied to the control of frequency sources, and the performance of digital compensation techniques. Prototypes of microcomputer-compensated crystal oscillators (MCXO's) have been developed to compare the compensation performance using the resonator as the temperature sensor against the use of an external sensor and verify the reduction of compensation errors due to thermal lags and hysteresis. The design of a CMOS integrated circuit for the MCXO is also included. A frequency correction method that does not modify the crystal resonance has been implemented in the circuit. This allows sensing of the temperature by means of the crystal and improving its long-term stability (aging). A new frequency comparator is also introduced. Its aim is to obtain the difference between two very close frequencies at its output, without being affected by the phase variations that the new frequency correction method and the digital circuit introduce. This detector has been implemented to get a high-resolution thermometric frequency and to realize a frequency-locked loop that includes a crystal controlled local oscillator, allowing the use of the MCXO as a good short-term stability source. >

The modulational method of the precision quartz-crystal oscillators and standards frequency stabilization

Abstract: A new trend in self-contained (without the use of quantum discriminators) frequency stabilization of oven control crystal oscillators (OCXO) and frequency standards is proposed and discussed in this paper. The method developing the trend is called a modulational method and is based on the use of metrological properties of natural volume oscillations of a quartz resonator (double-frequency and multifrequency oscillators are not used in this case). The concept is given of dynamic modulation characteristics of a quartz-crystal oscillator and basic relationships are found for their calculation in the field of unharmonic resonances of a quartz-crystal resonator. The construction principles of frequency stabilization systems are formulated substantiating mathematically the essence of the method. Basic ratios of modulating signals are determined, the solution of which provides a slight influence of the modulation signal on the Allan variance and spectral density of a quartz-crystal oscillator. The results of the practical use of the method are considered with the view of constructing a quartz-crystal oscillator with the adaptation to the environment temperature and a quartz-crystal frequency standard with the long-term frequency instability compensation.

Modulation type dual-mode oscillator intended for micro-chip realization

Abstract: Dual-mode oscillator is an oscillator based on simultaneous excitation of resonator modes. SC-cut resonators with B- and C- modes excitation are used as dual-mode most often. Each resonator mode has its own frequency vs. temperature dependence. When a resonator is being excited on two modes simultaneously, the mode frequency ratio is uniquely determined by temperature. This unique relation allows one to use C- and B- mode frequency ratio as a resonator proper thermosensor. This thermosensor has full spatial coincidence with a vibrated resonator plate and, therefore, it is an ideal resonator temperature measuring device. Due to quartz nature such sensor is very precise and stable. From the above reasoning dual-mode resonator is an ideal base for thermocompensated (TCXO) and ovenized (OCXO) oscillators, in the cases when we need to measure the quartz plate proper temperature with maximum accuracy. The concepts of dual-mode oscillators design have been discussed in this work. Considerable attention has been given to the constant B-mode excitation level keeping under external factors effects and resonator motional resistance variation. The micro-chip realizable dual-mode oscillator circuit is given. To demonstrate the validity of ideas the interim prototype of micro-chip dual-mode oscillator have been investigated. The main result of this work is that we show that dual-mode oscillators could be realized as a small-size micro device.

Internal heated quartz resonator with low sensitivity to an accelerator

Abstract: The paper describes results of development of the internal heated quartz resonator novel design. Such a resonator is built on composite heating of the crystal plate technique and possesses a unique compromise of high frequency stability with 15 s warm-up time, 4 mA heating current and less than 5/spl middot/10/sup -10/ 1/g acceleration sensitivity. The paper shows that the performances of the oscillator based on the IHR are very attractive for various global radionavigation and communication mobile systems.

Acceleration charge sensitivity in AT-quartz resonators

Abstract: The behavior of AT-quartz resonators subject to acceleration is studied. For an AT-strip resonator with cantilever mounting, piezoelectric theory predicts that excitation of the pure lowest frequency flexural mode of vibration generates no charge. However, experiments show electromechanical resonance corresponding to this mode for sinusoidal support motion normal to the plane of the crystal with no applied electric field. An amplifier with a voltage follower first stage senses charge output from the crystal. Shielding is required to reduce sixty hertz and drive frequency electromagnetic interference. Measurement of resonant frequency and damping factor for the lowest frequency flexural mode is reported for a group of 17.76 MHz oscillator crystals. This mode is responsible for crystal breakage in some portable communications products. Significant variation in sensitivity among crystals was observed. Charge sensitivity of this mode is attributed in part to mechanical coupling to other modes involving torsion and lateral flexure.

One-pin integrated crystal oscillator

Abstract: A one-pin integrated crystal oscillator in a Colpitts configuration employs a differential amplifier, provided with a feedback network, as an input gain stage. This achieves an enhanced stability and independence from temperature variation, a high Q figure, and a short start-up with a relatively small area of integration.

A single bridge resonator for low consumption OCXO

Abstract: A Single Bridge Resonator (SBR) concept has been previously proposed. This quartz resonator is designed as an element of a 10 MHz ovenized oscillator, the power consumption of which is limited at 200 mW over the operating range [-20/spl deg/C, +70/spl deg/ C] while its warm-up time is less than 3 minutes at +20/spl deg/C. The results obtained from the first prototype revealed some weaknesses. This paper provides a brief review of its main features and gives also a presentation of a new device attempting to correct the defaults of the first one. Three essential changes have been decided in order to achieve a better temperature control and to decrease the thermal gradients and their effect upon frequency. After the required coverage of these topics, we comment on the experimental results obtained from the modified prototype. The emphasis is still essentially placed on the thermal behavior of the S.B.R.: warm-up time, power consumption, frequency stability over the operating temperature range.

DTXCO thermal converter realized by means of a metal film temperature sensor deposited on the crystal plate

Abstract: Temperature compensated crystal oscillator parameters are dependent to great extent on the accuracy of crystal temperature measurements. The most prominent results were attained for DTCXO with resonator-temperature sensitive element configuration based on dual-mode excitation principle. In this case parameter high stability is attained and the temperature lag between temperature sensor and a measurement object is practically avoided. The investigation of an alternative crystal temperature measurement procedure shows that high DTCXO performances can be attained without dual-mode excitation. A thin metal film deposited along the crystal plate contour is used as a primary thermosensor. To increase the stability and the accuracy of temperature measurement a thermal converter had been developed using the principle of digital-analog system of automatic frequency control. Using by way of example a simple DTCXO with AT-cut crystal and piece-wise compensation function theoretic and experimental investigation were carried out.