Showing papers on "Crystal oven published in 2001"

Method and apparatus for controlling oscillation amplitude and oscillation frequency of crystal oscillator

Abstract: A circuit controls an oscillation amplitude of a crystal oscillator including a crystal resonator, a current source supplying a bias current, and an output transistor coupled to the crystal resonator and the current source. The circuit includes a peak detector for detecting a peak voltage of an output signal of the crystal oscillator, and a controller coupled to the peak detector and to the current source for controlling the current source in accordance with a difference between the peak voltage and a target voltage, the target voltage being set to be substantially equal to 2Vth, where Vth is a threshold voltage of the output transistor. A frequency control circuit controls a first switched-capacitor array and a second switched-capacitor array coupled to the crystal resonator, and alternately switches a unit capacitor in the first switched-capacitor array and a unit capacitor in the second switched-capacitor array based on a frequency control signal.

Digital indirectly compensated crystal oscillators

Abstract: A method and system for compensating for thermally-based frequency fluctuations of a piezoelectric crystal. A characterization of the frequency-temperature response of the crystal is stored in a memory. During operation, a host system is provided with the crystal's uncompensated frequency, the temperature of the crystal, and frequency correction values stored in the memory. The host system may then determine a compensated frequency by retrieving, or deriving through interpolation, a frequency correction value from the data provided in the memory.

ADOQ: a quartz crystal oscillator simulation software

Abstract: This paper presents the actual state of a computer program especially designed to simulate the behavior of quartz crystal oscillators. The program is based on the fact that the current through the quartz crystal is almost perfectly sinusoidal. Consequently the oscillator can be modeled by a resonator across a nonlinear impedance that depends only on the current magnitude through it. The resonator being replaced by a current source, the nonlinear impedance of the amplifier is computed from a series of transient analyses performed at the resonator frequency. When the steady state is reached, the resonator impedance is exactly equal and of opposite sign to the amplifier impedance. This identity allows one to compute the oscillation amplitude and the frequency shift with respect to the resonator frequency. This computation does not require to perform unacceptable long transient analyses in case of high-Q oscillator. Our program is intended to help the designer in checking or improving oscillator circuit design. From the Spice netlist, it enables the user to compute the steady state features of the oscillator, namely frequency and amplitude. Then, the user can study the effect of temperature change on any components or the influence of quartz characteristic. It is also possible to perform accurate oscillator sensitivity calculation to various parameters (component value, supply voltage, ...) as well as worst case analysis.

Programmable oscillator circuit and method

Abstract: A programmable crystal oscillator is provided having a memory for storing frequency-defining parameters. Typically, one of these parameters is used to program an adjustable capacitive load circuit coupled to a crystal to thereby adjust the crystal source frequency. Additional parameters are used to program the output frequency of a phase locked loop circuit coupled to receive the adjusted source frequency. A further parameter can also be used to divide the output frequency of the phase locked loop circuit to supply a specified output frequency. The oscillators can be manufactured as generic programmable crystal oscillators without regard for output frequency and then quickly programmed to produce customer-specified output frequencies with a high degree of accuracy.

Precision oven-controlled crystal oscillator

Abstract: A precision oven-controlled crystal oscillator (10) uses an adjustment feedback signal that, when mixed with a reference signal from a stable reference oscillator (32), accurately controls the generation of an output signal from a voltage controlled crystal oscillator (38). An OCXO according to the invention has high stability and high accuracy. The digital OXCO can be manufactured at low cost, and is particularly beneficial for Code Division Multiple Access (CDMA) base station applications in cellular communication networks and the like.

Temperature processing of an ultra stable quartz oscillator

Abstract: Commonly, the required short-term frequency stability of an ultra stable quartz crystal oscillator (USXO) is a few parts in 10/sup -13/ for averaging times of a few seconds. Moreover, the USXO must typically achieve a relative frequency variation of a few parts in 10/sup -10/ over a temperature range from -30 to +70/spl deg/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.

Design of a cryogenic dual-mode resonator for a fly-wheel oscillator for a cesium frequency standard

Abstract: A dual-mode Sapphire Loaded Cavity (SLC) resonator has been designed and optimized with the aid of finite element software. The resonance frequency was designed to be near the frequency of a Cs atomic frequency standard. Experimental tests are shown to agree very well with calculations. The difference frequency of two differently polarized modes is shown to be a highly sensitive temperature sensor in the 50 to 80 K temperature range. We show that an oscillator based on this resonator has the potential to operate with fractional frequency instability below 10/sup -14/ for measurement times of 1 to 1000 seconds. This is sufficient to operate an atomic clock at the quantum projection noise limit.

Design Technique for Analog Temperature Compensation of Crystal Oscillators

Abstract: For decades, the quartz crystal has been used for precise frequency control. In the increasingly popular field of wireless communications, available frequency spectrum is becoming very limited, and therefore regulatory agencies have imposed tight frequency stability requirements. There are generally two techniques for controlling the stability of a crystal oscillator with temperature variations of the environment. They are temperature control and temperature compensation. Temperature control involves placing the sensitive components of an oscillator in a temperature stable chamber. Usually referred to as an oven-controlled crystal oscillator (OCXO), this technique can achieve very good stability over wide temperature ranges. Nevertheless, its use in miniature battery powered electronic devices is significantly limited by drawbacks such as cost, power consumption, and size. Temperature compensation, on the other hand, entails using temperature dependent circuit elements to compensate for shifts in frequency due to changes in ambient temperature. A crystal oscillator that uses this frequency stabilization technique is referred to as a temperature-compensated crystal oscillator (TCXO). With little added cost, size, and power consumption, a TCXO is well suited for use in portable devices. This paper presents the theory of temperature compensation, and a procedure for designing a TCXO and predicting its performance over temperature. The equivalent electrical circuit model and frequency stability characteristics for the AT-cut quartz crystal are developed. An oscillator circuit topology is introduced such that the crystal is operated in parallel resonance with an external capacitance, and equations are derived that express the frequency stability of the crystal oscillator as a function of the crystal’s capacitive load. This relationship leads to the development of the theory of temperature compensation by a crystal’s external load capacitance. An example of the TCXO design process is demonstrated with the aid of a MATLAB script.

Digitally temperature compensated DDS

Abstract: A a direct digital frequency synthesizer incorporating compensation of frequency versus temperature (f-T) dependency of reference crystal oscillator is presented. The frequency instability of the synthesizer is /spl plusmn/0.1 ppm in a wide temperature range (-40/spl deg/C to +85/spl deg/C).

Cryogenic high-Q microwave resonators for stable oscillators

Abstract: Cryogenic microwave resonators have a strong potential as frequency stabilising elements for oscillators to be used in advanced radar systems and high-bitrate microwave communication links. Depending on frequency, either 2D planar HTS-resonators, HTS-shielded sapphire TE/sub 011/ resonators or cryogenic sapphire whispering-gallery mode resonators represent the best compromise between resonator quality factor and size. We have built and tested an all-cryogenic oscillator based on a WG-resonator at f=23 GHz. Phase noise measurements indicate values superior to quartz stabilized oscillators. A two-step electric frequency tuning consisting of an integrated varactor phase shifter and a dielectric plunger moved by a piezomechanical transducer is introduced to compensate frequency drifting with temperature. For further improvement of long-time frequency stability we have developed rutile-sapphire composite dielectric resonators. Due to the opposite sign of the temperature slope of the dielectric constant of sapphire and rutile a turning point appears in the temperature dependence of the resonance frequency. Employing a moderate temperature stabilization as good as a few millikelvin around the turning point at T=78 K, we have demonstrated a long time frequency stability at least as good as for oven controlled quartz oscillators.

Is an oscillator based measurement adequate in a liquid environment

Abstract: Oscillator based measurements with quartz crystal resonators are analyzed. The investigations have shown, that classical thickness monitors and also 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 which is representing the damping of the quartz resonator. Further on 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.

Method of evaluating quality of crystal unit

Abstract: A method of evaluating quality of a crystal unit, capable of performing quantitative measurement of an actual operation of a crystal unit which is to be oscillated in an actual oscillator to ensure an accurate quality evaluation, is provided. The method includes increasing a DC input voltage of a crystal oscillator, the crystal oscillator having at least one AGC amplifier whose amplification rate varies depending on the DC input voltage and having a crystal unit connected thereto, measuring a maximum value of the DC input voltage at a start of oscillation of the crystal oscillator, and evaluating quality of the crystal unit by the measured maximum value.

Frequency stable oscillators based on cryogenic whispering gallery mode resonators

Abstract: An all-cryogenic oscillator consisting of a frequency tunable sapphire resonator, a high temperature superconducting filter and a PHEMT amplifier was designed for the K-band frequency range and investigated. Sapphire whispering-gallery mode resonators possess high quality factors of about several millions due to the advantage of the strong electromagnetic field confinement. As a result the phase noise measured for the oscillator exhibits very low values in comparison to conventional oscillators. In addition, the effect of small rutile-platelets on the long-term temperature stability is measured and discussed. We have found that our composite resonators with rutile filling factor slightly below 1% exhibits a turning point in the temperature dependence of the resonance frequency at about 65-78 K. This results in a long time frequency stability as good as for oven controlled quartz oscillators by maintaining a high resonator quality factor in the 10/sup 7/ range at 10 GHz.

Application of the computer-aided analysis for modeling the behavior of a TCXO

Abstract: Quartz crystal oscillators for many radio frequency (RF) applications must provide a high-frequency stability in a wide temperature range. To do this, a temperature compensation network is commonly included. This study analyzes and determines the frequency behavior of an oscillator circuit with variations in temperature and shows how simulation may be employed for the design of high-stability quartz crystal oscillators. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 22–32, 2001.

Study of the damping processes in thickness shear mode resonator chemical sensors

Abstract: This work illustrates an alternative method of extracting signals from thickness shear mode resonator sensors. The basic idea consists of modulating the voltage supply of an oscillator circuit driven by a quartz element. The sensor signal can then be obtained measuring the time decay of the output signal in the off state, where some energy, stored in the on state, is released in the form of a damping oscillation. It has been experimentally proven that the time decay in the off state can be reproducibly related to the quartz loading by a remarkable sensitivity function. This paper shows most of the results obtained so far by this technique and discusses the general performance, advantages and disadvantages as well as comparison with the standard frequency measurement technique.

Phase noise measurements in dual-mode SC-cut crystal oscillators

Abstract: This paper describes the phase-noise characteristics and the analysis model of an SC-cut dual-mode oscillator. The C mode phase-noise sideband levels of -124 dBc at 10 Hz and -154 dBc at 10 kHz have been demonstrated using a dual-mode oscillator that simultaneously excited the C and B mode of a 10-MHz, third overtone, SC-cut crystal resonator. Based on Leeson's model, a phase-noise analysis model for dual-mode oscillators has been proposed also. Actual phase-noise levels of the C mode in dual-mode oscillation corresponded well to results calculated from the proposed model.