Showing papers on "Crystal oven published in 2011"

Next generation AT-cut quartz crystal sensing devices

Abstract: Generally, AT-cut quartz crystals have a limited scope of use when it comes to high-precision measurement of very small impedance changes due to their nonlinear frequency-temperature characteristics in the range between 0 °C and 50 °C. The new method improving quartz oscillator frequency-temperature characteristic compensation is switching between two impedance loads. By modifying the oscillator circuit with two logic switches and two impedance loads, the oscillator can switch oscillation between two resonance frequencies. The difference in resonance frequencies compensates the frequency-temperature characteristics influence as well as the influence of offset and quartz crystal ageing. The experimental results show that the new approach using the switching method highly improves second-to-second frequency stability from ±0.125 Hz to ±0.00001 Hz and minute-to-minute frequency stability from 0.1 Hz to 0.0001 Hz, which makes the high-precision measurement of aF and fH changes possible.

Digitally controlled oscillator

Abstract: A digitally controlled oscillator is provided. The digitally controlled oscillator includes a pair of transistors cross-coupled to each other, a switched capacitor array coupled to the pair of transistors and a plurality of frequency tracking units coupled to the pair of transistors. The pair of transistors provides an output signal. The switched capacitor array tunes a frequency of the output signal. The frequency tracking units tune the frequency of the output signal to a target frequency. At least one of the frequency tracking units is capable of selectively providing a first capacitance and a second capacitance. A tuning resolution of the frequency tracking unit is determined by a difference between the first and second capacitances.

Unprecedented long-term frequency stability with a microwave resonator oscillator

Abstract: This article reports on the long-term frequency stability characterization of a new type of cryogenic sapphire oscillator using an autonomous pulse-tube cryocooler as its cold source. This new design enables a relative frequency stability of better than 4.5 × 10-15 over one day of integration. To the best of our knowledge, this represents the best long-term frequency stability ever obtained with a signal source based on a macroscopic resonator.

The design and implementation of a 120-MHz pierce low-phase-noise crystal oscillator

Abstract: The phase noise within the half-bandwidth of the loop is closely related to the loaded quality factor QL. The importance of loaded quality factor QL and the method of reducing phase noise on the basis of improving QL are analyzed in this paper. Formulation of QL is derived from analysis of the Pierce oscillator circuit, and calculated with commercial numerical analysis software. According to the results, we can draw a conclusion that QL is explicitly related to circuit pa rameters. Based on this conclusion, a design of the prototype 120-MHz crystal oscillator is presented and the experiments are carried out. The crystal resonator utilized is an SC-cut 5th-overtone crystal resonator with an unloaded quality fac tor Q0 of about 1.05 × 105. The circuit parameter values are adjusted to make QL reasonably higher, while maintaining an output amplitude of 2 to 3 dBm. The measurement results of near carrier frequency phase noise are -104 dBc/Hz at 10 Hz and -134 dBc/Hz at 100 Hz. Experimental results show that it is feasible to design a low-phase-noise crystal oscillator based on improving QL.

System and method for reducing temperature-dependent and process-dependent frequency variation of a crystal oscillator circuit

Abstract: In embodiments of the present disclosure, a method may include determining an ambient temperature of an oscillator. The method may also include estimating an approximate frequency of operation of the oscillator. The method may additional include determining a process-based compensation to be applied to a resonator of the oscillator based on the approximate frequency. The method may further include setting a capacitance of a variable capacitor coupled to the resonator in order to compensate for temperature-dependent and process-dependent frequency variation of the oscillator based on the ambient temperature and the process-based compensation.

Tcxo replacement for gps

Abstract: To determine the level of frequency drift of a crystal oscillator as a result of a change in the its temperature, the temperature of the crystal oscillator is sensed and used together with previously stored data that includes a multitude of drift values of the frequency of the crystal oscillator each associated with a temperature of the crystal oscillator. Optionally, upon initialization of a GPS receiver in which the crystal oscillator is disposed, an initial temperature of the crystal oscillator is measured and a PLL is set to an initial frequency in association with the initial temperature. When acquisition fails in a region, the ppm region is changed. The temperature of the crystal oscillator is periodically measured and compared with the initial temperature, and the acquisition process is reset if there is a significant change in temperature. The GPS processor enters the tracking phase when acquisition is successful.

Methods and apparatus for calibration and temperature compensation of oscillators having mechanical resonators

Abstract: Methods and apparatus for calibration and temperature compensation of oscillators having mechanical resonators are described. The method(s) may involve measuring the frequency of the oscillator at multiple discrete temperatures and adjusting compensation circuitry of the oscillator at the various temperatures. The compensation circuitry may include multiple programmable elements which may independently adjust the frequency behavior of the oscillator at a respective temperature. Thus, adjustment of the frequency behavior of the oscillator at one temperature may not alter the frequency behavior at a second temperature.

Fundamental wave/overtone crystal oscillator

Abstract: Provided is a fundamental wave/overtone crystal oscillator to obtain fundamental wave oscillation and overtone oscillation with one crystal unit and to optimize the excitation current depending on the fundamental wave oscillation and the overtone oscillation. The fundamental wave/overtone crystal oscillator includes a crystal unit that oscillates with fundamental waves or with overtones, and an oscillator circuit that amplifies an excitation current from the crystal unit and outputs an oscillatory frequency. A capacitor Cf and a capacitor Co are connected in parallel with the base of a transistor in the oscillator circuit as well as the emitter. A switch is provided so as to connect or disconnect the capacitor Cf with respect to the circuit in response to a switching signal. The switch turns ON when the crystal oscillator oscillates with fundamental waves, and turns OFF when the crystal oscillator oscillates with overtones.

Performances of Monolithic Micro-Oven Heated SAW and STW Resonators

Abstract: Frequency stability of resonators used in low noise oscillators is typically achieved by encasing the resonator or the complete oscillator in a temperature-controlled oven. This method is preferred over electrically pulling the resonator which results in a lower loaded Q. The oven approach introduces long warm-up time, increased size, and adds considerably to the total power dissipation of the oscillator. The objective is to develop an oven structure which drastically reduces both warm-up time and power dissipation. A novel micro-oven heated resonator structure 1 will be presented. The structure includes the resonator, resistive heaters and temperature sensors all formed with the same fabrication process as for a resonator alone. The temperature sensor is formed by meander-connection of groups of reflective grating strips resulting in a direct temperature measurement of the active part of the resonator die. The micro-oven heated resonator structure and characteristics of both SAW and STW resonators and performances in oscillators will be presented. Warm-up times of less than 5 seconds at –40°C are achieved. Direct heating of the active surface of the SAW resonator chip drastically reduces warm-up time and heater power consumption over previous ovenized resonator approaches. The micro-oven electronics requires little additional space resulting in a compact oscillator. 1 patent applied for

Expected quality factor of a simple tuned oscillator

Abstract: A positive feedback system oscillating under self-sustained mode is shown to have an extremely high gain. Modeled as one port, the expected Q is much higher than the loaded Q-factor of the resonator. With just thermal noise present, random phase/frequency deviation is linear. Centered about the oscillator frequency ω0, noise frequency on both sides is more amplified with decreasing separation distance. Ultimately, frequency pulling may result in synchronous locking with hysteresis, which occurs be cause a real oscillator displays a truncated limiting curve. Once locked onto a signal, smaller levels are ignored. A new approach to the design and characterization of a simple tuned oscillator is offered: According to the phenomenon of injection locking, there exists an expected quality factor relating the shape of the truncated limiting curve to an ideal curve. In this paper, synthesis and innovative analytical methods of academic interest are revealed: 1) application of the transducer loss method is revised to establish a new method for oscillator characterization; 2) a transparent method of normalizing a two-port network in the presence of white noise is developed; and 3) in quartz crystal controlled oscillators, characterization of the noise originating from an equivalent noise-resistance determined from parameter of the quartz crystal is proposed. It is shown that the two-port model can also be approximated on a one-port basis. In conclusion, a sample of closed form estimation of expected Q-factor order of magnitude of piezoelectric resonator oscillators is calculated.

A 0.6V 200kHz silicon oscillator with temperature compensation for wireless sensing applications

Abstract: This paper presents a silicon oscillator suitable for low-cost and low-power wireless sensing applications. With the comparisons of ring oscillators in different temperature coefficients, the frequency of an internal ring oscillator is estimated and parameterized by a second-order polynomial. Accordingly, the output clock is compensated in a frequency division fashion. The oscillator is implemented in 90-nm CMOS technology with an area of 0.04mm2. Operating at 0.6V, the output frequency is within 200±1kHz over the temperature range of Ȓ25°C to 125°C with power consumption of 48µW.

Quartz Resonator Based, 0.12 μW, 32768 Hz Oscillator with ±100 ppm Frequency Accuracy

Abstract: A 0.12 μW power dissipation quartz oscillator with 32,768 Hz frequency was designed and fabricated. Stability of the oscillator versus power supply and temperature variations was measured. The design is suitable for the role of the RTC (real-time clock) or main system clock in low-power, battery-powered and energy harvesting systems.

Analysis and design of low-power - low-noise crystal oscillators accounting for electro-mechanical energy conversion aspects

Abstract: This paper presents an original multi-physics modeling methodology for the design and analysis of integrated crystal oscillators based on power-waves formulation. Conventional Barkhausen oscillation conditions criterion is derived in terms of reflection coefficients. Coupling module is introduced between the crystal resonator and the oscillator active-core in order to account for electromechanical energy conversion aspects. The proposed methodology is successfully applied to the design of low power and low noise integrated crystal oscillator in NXP-Semiconductors advanced BiCMOS technology. A phase noise better than −152dBc/Hz at 10KHz carrier offset with noise supply rejection better than −65dB are demonstrated.

Methods of frequency versus temperature compensation of existing crystal oscillators

Abstract: Methods for compensating the existing crystal oscillator frequencies in extended temperature ranges. These are utilizing existing crystal oscillators on any system design which may have quartz crystals with associated circuitry to deliver frequency or timing reference signals. They are increasing these existing circuitry's accuracy simply by adding small integrated circuit component.

Oven controlled MEMS oscillator

Abstract: A system for generating an output signal having a substantially stable frequency, the system comprising: an oven (2); a micromechanical oscillator (11) inside the oven, provided for oscillating at a predetermined frequency; an excitation mechanism associated with the micromechanical oscillator and being configured for exciting the micromechanical oscillator; a temperature control loop (71,83,84,88) associated with the micromechanical oscillator and comprising components (61,62) for detecting, evaluating and adapting the temperature of the micromechanical oscillator (11) according to a ratiometric principle with resistive sensing; a frequency output (87) for outputting the predetermined frequency of the micromechanical oscillator (11) as a basis for generating the output signal; said components may have a first resp. second temperature dependent characteristic, the second temperature dependency being different from the first temperature dependency such that the first and second characteristics intersect within a predetermined temperature range.

Temperature-corrected frequency control with crystal oscillators for initial frequency acquisition

Abstract: A communication terminal includes a crystal oscillator, a transceiver and circuitry. The crystal oscillator belongs to a specified type in which a dependence of an output frequency on temperature has one or more temperature dependence coefficients. The transceiver is arranged to operate an AFC loop having an initial frequency accuracy requirement that is more stringent than an uncompensated frequency accuracy of the crystal oscillator. The circuitry is arranged to determine output frequencies of the crystal oscillator at respective operating temperatures, to compute the temperature dependence coefficients based on the output frequencies and operating temperatures, to correct a frequency error in the output frequency using the dependence and the temperature dependence coefficients, to ascertain that the corrected frequency error meets the initial frequency accuracy requirement, and to subsequently correct a frequency of the received signal using the AFC loop.

Control and monitoring of the quartz crystal current in the quartz crystal oscillator

Abstract: Novel circuit design is proposed for low-frequency quartz crystal oscillator circuit with the enhanced control of excitation level. The function of the limiter circuit was analyzed on the base of the negative resistance of the CMOS-inverter quartz oscillator reviewed for the fundamental mode of a quartz crystal microbalance resonator, and appropriate gain control and drive current reduction were realized by adding a capacitor between one terminal of the quartz crystal and the ground level. Experimental result and the absolute value of the negative resistance are compared with the conventional Colpitts circuit. © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Understanding Pound-Drever-Hall locking using voltage controlled radio-frequency oscillators: An undergraduate experiment

Abstract: We have developed a senior undergraduate experiment that illustrates frequency stabilization techniques using radio-frequency electronics. The primary objective is to frequency stabilize a voltage controlled oscillator to a cavity resonance at 800 MHz using the Pound-Drever-Hall method. This technique is commonly applied to stabilize lasers at optical frequencies. By using only radio-frequency equipment it is possible to systematically study aspects of the technique more thoroughly, inexpensively, and free from eye hazards. Students also learn about modular radio-frequency electronics and basic feedback control loops. By varying the temperature of the resonator, students can determine the thermal expansion coefficients of copper, aluminum, and super invar.

Development of an anti-vibration crystal oscillator for reducing vibration-induced phase noise

Abstract: Crystal oscillators are acceleration sensitive devices. Vibration will degrade the phase noise of crystal oscillators in many applications such as aircrafts, ground vehicles, and even in the laboratory due to cooling fans, footsteps, etc. This paper presents development of an anti-vibration crystal oscillator (AVXO) for reducing phase noise degradation due to mechanical vibration on the crystal oscillator. The approach for reducing phase noise degradation starts with choosing crystal resonators, designing isolators, and simulating the transmissibility of the isolator and the phase noise of the AVXO under random vibration. The measured phase noise is typically better than −145dBc/Hz at 1 kHz offset frequency from the carrier frequency of 100 MHz, when crystal oscillators are under operational vibration condition. The measured results show that the isolator in the AVXO is actually providing in excess of 40 dB improvement at 1 kHz offset frequency.

Research on Character of Integrated Quartz Crystal Resonators

Abstract: The force sensitive characteristic of integrated quartz crystal resonator assembled on one quartz crystal substrate with a certain radial direction force are studied, and it is also studied that the force sensitive characteristic of output frequency which is the mixing frequency by resonant frequency corresponded to the resonators in the different position of the same quartz crystal wafer outputted in difference frequency way. The research result shows the force sensitive characteristic of AT-cut integrated three-electrode quartz crystal resonator outputted in difference frequency way is 1.3 times of that of the traditional single-electrode resonator. The force sensitive characteristic of the integrated four-electrode resonator is a little bit smaller, but two sets of output can be obtained at the same time. The frequency stability of all integrated quartz resonator can get to the magnitude of 10-10 and relative frequency variation is about ±5ppm in the range of -50°C to 60°C.

Tunable terahertz radiation source based on difference frequency cherenkov effect and modulation method

Abstract: The invention relates to the non linear optical frequency conversion. To realize output of high power THz wave which can be continuously tuned, and stable running at room temperature, the technical scheme used by the invention is that: a tunable terahertz radiation source based on difference frequency cherenkov effect is composed of a laser device, a frequency doubling crystal, a double wavelength parametric oscillator, a harmonic mirror, a polarization filter, a combined beam mirror, a column lens and a difference frequency crystal; the harmonic mirror is placed between the frequency doubling crystal and the double wavelength parametric oscillator; the double wavelength parametric oscillator is II type phase matching KTP (Potassium Titanyl Phosphate) crystal OPO (Optical Parametric Oscillator); the polarization filter, the combined beam mirror and the column lens are arranged between the parametric oscillator and the difference frequency crystal; the difference frequency crystal is amagnesium oxide doped lithium niobate crystal with molecular formula of MgO:LiNbO3 or MgO:LN, and the generated THz wave is coupled and output by an Si prism on the side surface of the difference frequency crystal. The tunable terahertz radiation source based on difference frequency cherenkov effect is mainly applied to the optical frequency conversion.

A New Explanation Crystal Oscillator with Injection Locking Phenomenon

Abstract: In this research, a new explanation and design crystal oscillator based on injection locking phenomenon is proposed. The crystal oscillator is viewed as a regular oscillator whereas is ac small input signal is its forced function. In this work, a crystal is considered to be a very small sinusoidal signal generator. To guarantee that the injection locking phenomenon is occurred the frequency of the crystal must be very close to that of an oscillator. Then the output frequency of the oscillator is identical to the crystal’s frequency. With this phenomenon, a new design crystal oscillator is presented. It is focused on designing basis oscillator whose frequency is close to the crystal’s frequency. In addition, the appropriate position for feeding the forced function to the basis oscillator is determined. In examination, the Wein-brigde oscillator is employed to be an example to describe this proposed technique where the obtained experimental results are in accordant well with the theoretical result.

Production of quartz crystal units with compensation for mechanical and termical stresses

Abstract: The paper describes the development and production of high quality quartz crystal units, intended for use in oscillators OCXO (oven control crystal oscillator) type. The crystal units are based on SC cut of high-quality quartz crystal. They are characterized with high stability oscillation and very low phase noise, especially at low offset frequencies.