Vladimir Stofanik

Dual-Mode Crystal Oscillator with Simultaneous Excitation of Two Overtones in a Stress Compensated Quartz Resonator

The paper introduces novel dual-mode crystal oscillator (DMXO) that employs a standard 10 - MHz 3rd overtone stress compensated (SC) quartz resonator. In the DMXO, the two overtones (c-modes) of the SC-cut resonator are simultaneously excited: the 3rd overtone and the 5th overtone. The ability of utilization of the two excited overtones to implement the resonator self-thermometry we have evaluated. The resonator self-temperature-sensing method eliminates temperature offset and lag effects, since no external temperature sensor is used. Eventual applications of the DMXO with excitation of the two overtones include the stabilization of the SC-cut resonators temperature as well as compensation for frequency shifts due to the variations of the ambient temperature.

Investigation of self-temperature-sensing of SC-Cut with simultaneous excitation of two higher overtones in dual-mode crystal oscillator

This paper deals with evaluation of self-temperature-sensing of stress compensated (SC) quartz resonator with simultaneous excitation of two higher overtones - the slow thickness-shear modes (i.e. the c-modes) in dual-mode crystal oscillator (DMXO). Two different combinations of overtones simultaneously excited in the standard 10-MHz 3rd overtone SC-cut resonator are compared here: - the 5th overtone excited together with the 3rd overtone; - and the 7th overtone excited together with the 3rd overtone. Possible applications of the self-temperature-sensing include: stabilization of the SC-cut resonatorpsilas temperature with excellent accuracy; as well as precise compensation for frequency shifts due to the variations of the temperature in the SC-cut resonator surrounding.

Multi-mode crystal oscillator for simultaneous excitation of three thickness-shear modes in stress compensated resonator

This paper deals with evaluation of self-temperature-sensing of stress compensated (SC) quartz resonator with simultaneous excitation of three higher overtones - the slow thickness-shear modes (i.e. the c-modes) in multi-mode crystal oscillator (MMXO). We have designed the MMXO especially for excitation of three c-modes in standard 10-MHz 3rd overtone SC resonators: the 3rd overtone, the 5th overtone and the 7th overtone. Each excited mode has its own frequency vs. temperature characteristic that can be measured and approximated as well. Simultaneous excitation of the three modes of vibrations in the volume of the resonator enables us to enhance the self-temperature-sensing. Consequently, in addition to compensation for frequency shifts due to variations of the resonators temperature, also frequency shifts caused by different aging rates of the particular modes can be identified autonomously (without necessity for any external frequency reference).

RF Field Orientation Influence on the Specific Absorption Rate in a Biological Object

The influence of radio-frequency (RF) field orientation on specific absorption rate (SAR) in a human body is investigated in this paper. Three basic field orientations have been simulated: electric field vector, magnetic field vector and Poynting vector parallel to the longitudinal axis of a human body. The influence has been investigated in frequency range from 10 MHz to 2450 MHz with assistance of CST Microwave Studio program environment. Here the homogeneous ellipsoid, as a human body model, is irradiated by plane wave, representing far-field zone of antenna.

Digitally temperature compensated DDS

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).

Self-identification of differences between aging rates of two frequencies excited in the dual-mode crystal oscillator

In this paper we introduce an extension of the self-temperature-sensing of stress compensated (SC) quartz resonator based on simultaneous excitation of two overtones (3rd and 5th overtone) - the slow thickness-shear modes (i.e. the c modes) in dual-mode crystal oscillator (DMXO). The extension is based on implementation of a self-identification of the differences between aging rates (long-term frequency instabilities) of the two modes frequencies simultaneously excited in the quartz resonator. Processing of two excited c modes frequencies enables to predict their shifts due to resonators temperature variations in a wide range, where the characteristics of the c modes are free from significant anomalies.

Direct digital synthesizer clock frequency versus temperature dependency compensation using two look-up tables

The paper describes a novel approach of static frequency vs. temperature dependency compensation of a direct digital frequency synthesizer clock signal. The compensation significantly reduces the frequency vs. temperature dependency of synthesized signals over a wide range of operating temperatures. The clock signal, which samples the direct digital frequency synthesizer, is excited by a dual-mode crystal oscillator. Since the crystal self-thermometry is used, temperature information is obtained directly from the crystal itself rather than from an external sensor and temperature offset and lag effects are eliminated. The designed compensation module can be implemented effectively within many popular field programmable gate arrays or programmable logic devices available today, e.g. using any Spartan-II family device (Xilinx, Inc.).

Digital recursive oscillator with reduced frequency versus temperature dependency utilizing a dual-mode crystal oscillator

The paper deals with a reduction of static frequency vs. temperature (f-T) dependency of digitally generated sinusoidal signals. The f-T dependency reduction is based on a self-temperature-sensing of a quartz crystal in dual-mode crystal oscillator, which produces the reference clock. We have proposed a digital oscillator, which automatically compensates the f-T dependency of its sampling clock over a wide range of operating temperatures. Numerical accuracy limitation of the oscillator due to finite word-length arithmetic is also analyzed in this article

Improvement of short-term frequency stability of the Chip Scale Atomic Clock

Utilization of the Chip Scale Atomic Clock (CSAC) today gives great potential for wide range of strategic systems requiring superior long-term frequency stability. Compared to CSAC, an OCXO has many drawbacks, e.g. it has larger long-term frequency instabilities (aging rate), longer warm-up time and higher power consumption. On the other hand, the main disadvantage of the CSAC is the higher phase noise. In this paper we describe a method of improvement of the CSAC SA.45s short-term frequency stability (phase-noise) using an external OCXO (MTI 230-0827) syntonized to the CSAC. In the low power mode, the CSAC SA.45s consumes less than 20 mW of power; however it operates as simple TCXO and over a full operating temperature range, the frequency stability is limited to ±1 ppm. In the last part of the paper we introduce combined low power clock system that can achieve frequency stability ±0.01 ppm over a wide temperature range, while consuming similar power.

Crystal Oscillator Design for Using in Sensor Technique

The paper deals with a crystal oscillator with piezoelectric quartz resonator connected between base of a bipolar junction transistor and ground. The main attention is devoted to the influence of loss resistance of the used piezoelectric resonator to the gain at the corresponding open feedback loop.