M. Mourey

Phase noise measurements of 10-MHz BVA quartz crystal resonators

In this paper, we review a new piece of equipment that allows one to characterize the phase noise of crystal resonators using a phase bridge system with carrier suppression. This equipment allows one to measure the inherent phase stability of quartz crystal resonators in a passive circuit without the noise usually associated with an active oscillator. We achieved a system noise floor of approximately -150 dBc/Hz at 1 Hz and -160 dBc/Hz, at 10 Hz. A SPICE characterization of the carrier suppression system is given. An investigation of the phase modulation (PM) noise in 10 MHz BVA, SC-cut quartz crystal resonator pairs is presented.

Predicting phase noise in crystal oscillators

In order to predict the phase noise in crystal oscillators an enhanced phase-noise model has been built. With this model, the power spectral densities of phase fluctuations can be computed in different points of the oscillator loop. They are calculated from their correlation functions. The resonator-caused noise as well as the amplifier-caused noise are taken into account and distinguished. To validate this enhanced model, the behavior of a batch of 10 MHz quartz crystal oscillators is observed and analyzed. The tested batch has been chosen in a facility production. Their associated resonators have been selected according to the value of their resonant frequency and their motional resistance. Open-loop and closed-loop measurements are given. The phase noise of the overall oscillator working in closed loop is provided by the usual active method. Theoretical and experimental results are compared and discussed

Phase noise limitation due to amplitude frequency effects in state-of-the-art quartz oscillators

During the past two decades very important advances have been accomplished in reducing the phase modulation (PM) noise in state-of-the-art bulk wave quartz crystal oscillator. Various limitations have been significantly reduced, especially those related to dynamic temperature fluctuations, temperature gradients, 1/f noise in the electronic and amplitude frequency effects. Amplitude frequency effects have been studied in the past because they are so large in AT-cut resonators. The introduction of the SC-cut significantly reduced the sensitivity to amplitude fluctuations as well as the sensitivity to temperature fluctuations. The amplitude frequency effect in modern SC-cut resonators at 5 or 10 MHz is, however, far from negligible and its importance relative to temperature effects and 1/f amplifier noise must now be reexamined to chart the path to further advances in short-term stability. In this paper we show comparisons of the amplitude frequency effect in traditional 5 MHz AT-cut resonators to our results obtained with 5 MHz BVA AT-cut, 5 MHz BVA SC-cut, 10 MHz BVA AT-cut and several designs of 10 MHz BVA SC-cut resonators. We also compare these measurements with those obtained from 100 MHz resonators. A simple model in which an additional noise source arising from the amplitude frequency effect is introduced in the input of the resonator excited at a given power. This permits us to estimate the contribution of the amplitude frequency effect to /spl sigma//sub y/(/spl tau/).

Comparison of the effects of intermodulation and amplitude to phase conversion in a transistor stage upon the oscillator phase noise

Phase noise reduction is still an important goal in ultra stable oscillator design. As a contribution to understanding of phase noise generation, two identified mechanisms are analysed. The first one involves nonlinearities. It may be, for example, the nonlinear V-I relationship of the base-emitter transistor junction. In that case this nonlinearity causes the noise spectrum of transistor to be transferred around the RF signal carrier by means of intermodulation. There is no way to avoid such a nonlinearity in an oscillator. For this reason the amplitude of the RF signal is limited. The second one deals with conversion of amplitude noise to phase noise. This may be for example the effect of the parasitic capacitance of the collector-base junction modulated by the amplitude noise or by the signal itself. The effects of those two mechanisms are analysed with help of a simulation software and results are applied to the closed loop of a typical 10 MHz quartz crystal oscillator. Consequences on the power spectral density of its phase fluctuations and the resulting time-domain instabilities of the oscillator frequency are presented and discussed.

A space oscillator with cylindrical oven and symmetry

A cylindrical oven whose axis is the axis of the 10 MHz quartz resonator (in HC 40 can) is studied. Thermal flux is canalized on its axis at a place where the thermistor is located. Thermal exchanges include conduction and radiation effects, reduced, however, by the use of a dual envelope. The oven is studied through a scheme which uses electric analogs, and results are obtained for external temperatures between -25 degrees C and +60 degrees C. The thermistor is located on the resonator can where temperature is very close to the turnover point. The analytical modeling uses oven symmetry. Thermal regulation design includes a frequency analysis between 0.001 Hz and 10 Hz, with a 60-dB gain. A response analysis to temperature steps and to linear temperature variation (0.5 degrees C/mn) is also performed. The thermal gain and dynamical behavior of oven electronics is deduced. Insertion of a correction network with phase advance in oven electronics yields a fast oven response. The oscillator improvements in space conditions are described.<<ETX>>

A phase noise model to improve the frequency stability of ultra stable oscillator

The goal of this study is to set up an improved model of the frequency stability behavior of the oscillating loop. A computer aided analysis is performed in which the transfer functions of the loop can be entirely described. This allows to predict phase noise performance of a given design. As a result the model provides ultimate limits of an oscillator concerning f/sup 0/, f/sup -1/, f/sup -3/ and f/sup -4/ phase noise versus the quartz resonator parameters for a given electronics noise. The model can also be used the opposite way to determine electronics noise for desired performances of an oscillator. Basic definitions are first recalled. The paper includes a description of the improved model that we developed starting from the Leesons model. This improved model is in good agreement with experimental results obtained from 10 MHz crystal oscillators with SC cut quartz resonator.

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/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.

A single bridge resonator for low consumption OCXO

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.

An oscillator for space

These last years a new 10 MHz quartz crystal oscillator family has been designed in LCEP with the support of the French space agency (CNES). It is intended for space applications especially. In this paper, the description of its general features is followed by two parts. The first one described the methodology which has been developed for designing such an oscillator. This part deals with the modeling of noise as well as the mechanical and thermal structure of the oscillator. The second part summarizes main experimental results. This obviously includes the frequency stability of the oscillator and its behavior when various disturbances occur in its environment. We particularly took care of its sensitivity to external temperature changes at the atmospheric pressure and mainly under vacuum. Exhibited frequency sensitivities to a magnetic field and vibrations are also provided.

Phase noise study of quartz crystal resonators versus the radius of curvature

First measurements of the phase noise versus the radius of curvature of SC-cut resonators are given. Resonators with adherent electrodes are investigated and compared with unelectroded resonators. The phase noise measurements are obtained with a crystal resonator tester specifically designed to assist in the characterization of quartz crystal resonators.