Frequency Stability Of Oscillators Research Articles

Ultra-low-noise microwave oscillator with advanced phase noise suppression system

An advanced phase noise reduction technique has been developed to improve the short-term frequency stability of microwave oscillators. The technique is based upon an ultrasensitive microwave frequency discriminator with effective noise temperature close to its physical temperature. The phase noise spectral density of a 9 GHz microwave loop oscillator incorporating such a discriminator has been measured as -120 dBc/Hz and -150 dBc/Mz at offset frequencies of 100 Hz and 1 kHz, respectively. This performance is at least 25 dB better than current state of the art. The developed phase noise reduction technique is quite general and can have valuable implications for the design of various low phase noise microwave oscillators.

Precise measurement of resonance current and frequency characteristics of quartz oscillators for oven‐controlled crystal oscillators

AbstractThis paper presents a precise measurement method for obtaining the drive power dependency of frequency in highly stabilized quartz‐crystal oscillators. The method is aimed at improving the frequency stability of crystal oscillators and, in particular, oven‐controlled crystal oscillators (OCXOs). It uses a transistor Colpitts oscillation circuit which features excellent resolution and reproducibility of electrical current measurements as well as higher operating frequencies than those of conventional techniques such as transmission or reflection methods. In this paper, the authors demonstrated concepts of this method and a corresponding measurement system. The proposed method also was applied to SC‐cut crystal oscillators used in OCXOs which had shown nonsatisfactory frequency stability (discussed earlier by the authors). Here, the authors demonstrated that those problems were caused by frequency jumps in the oscillator frequency‐versus‐current characteristic. It was shown also that OCXO circuits with excellent reproducibility of temperature characteristics can be implemented by using an appropriate level of driving current to drive the quartz oscillator in the generation mode.

Oscillator performance from the time evolution of relative phase

An improved method is described for simultaneously evaluating the fractional frequency stability and phase noise spectrum of ultrastable microwave oscillators from a digitised recording of a zero Hertz beat waveform between two such oscillators. To illustrate the new technique results are presented from a study of two ultrastable cryogenic sapphire oscillators which have a fractional frequency stability near 10/sup -15/ at 1 s integration time.

Stability of oscillation frequency of ECL-based multivibrator

The stability (with temperature and power supply voltage variations) of the oscillation frequency f0 of an ECL-based multivibrator is considered. This circuit is a non-saturated multivibrator. Its operation is revised and an exact expression for calculation of f0 is obtained. Then the temperature coefficient and sensitivity to the power supply voltage are derived. The results were verified experimentally. Some recommendations on the choice of the external timing components are given.

SAW oscillator frequency stability at high temperatures

A broad overview of various factors affecting the frequency stability of surface-acoustic-wave (SAW) resonators is given. Two major causes of rapid degradation in the long-term frequency stability are the presence of a chromium interface between aluminum and quartz, and moderate to high drive levels in SAW devices with pure aluminum fingers, resulting in metal migration in the region of high thin-film stresses. On the other hand, devices with copper-doped aluminum electrodes maintained excellent long-term stability, even when operating at 175 degrees C and at moderately high drive levels. Experimental data on both the long-term and short-term frequency stabilities of SAW devices at 25 degrees C and 175 degrees C for moderate to high drive levels are presented. Results obtained for the frequency stabilities of SAW devices with pure aluminum and copper-doped aluminum electrodes are compared. It is shown that the short-term frequency stability of SAW devices with copper-doped aluminum electrodes is a few parts in 10(10), even at 175 degrees C and for moderately large drive levels. Overall, the best short-term frequency stability is found to be for a gate time of 0.1 s.

Frequency stability in resonator-stabilized oscillators

A simplified stability analysis of resonator-stabilized oscillators is carried out by using the describing function approach. On this basis a criterion for the evaluation and optimization of the frequency stabilization introduction in an oscillator by a resonating element with a large quality factor is proposed. In particular, a frequency-stabilization index which can be conveniently used in the design of highly stable oscillators is defined. The validity of this performance index has been verified in the design of microwave oscillators using dielectric resonators as frequency-stabilizing elements. >

A highly stabilized fet oscillator for ku‐band receiver

AbstractThe utilization of Ku‐band satellite broadcasting and satellite communication is progressing. A high stability of oscillation frequency is required for local oscillators of receiver converters used in such communication. Therefore, analytical and experimental examinations have been carried out for the oscillation principle and the stabilizing method for oscillators using a common drain GaAs FET without an external feedback circuit and a very high‐Q dielectric oscillator.First, the output admittance of the common drain FET oscillator is calculated using GaAs FET small‐signal parameters to clarify the oscillation principle. Next, the oscillation frequency characteristics are analyzed and it has been shown that it is necessary to reduce the variation of oscillator output susceptance with the applied voltage to stabilize the oscillation frequency. The addition of a capacitive admittance to the oscillator source output is effective for this purpose.In an oscillator with a 0.02 S capacitive stub formed at the source output, oscillation frequency of 10.678 GHz, temperature variation of less than 600 kHz (‐20°C ∼ +60°C), and phase noise of ‐95 dBc/Hz (offset frequency: °10 kHz) have been obtained.

Improved numerical technique for oscillator frequency stability analysis

The letter introduces a statistical quantity, termed the extended Hadamard variance, for the spectral analysis of the frequency fluctuations v(t) of an oscillator. The samples of the time series v(t) are the gated averages vτ or counts of a digital frequency counter spaced by the dead time τd. The analysis technique and the numerical algorithm combine the flexibility of the extended two-sample variance with a much higher resolution spectral analysis capability, as shown by experimental results. The limitations are also indicated.

Resolution in macroscopic measurements: progress and prospects

The standard quantum limits on several macroscopic quantities and the conditions for attaining these limits are evaluated. Possibilities for exceeding them by means of quantum nondemolition measurements are examined. The best frequency stability in self-excited oscillators, the smallest mechanical displacements, and the highest Q values of mechanical and electromagnetic resonators which have been achieved are reviewed. The outlook for improving the sensitivity in several gravitational experiments is evaluated.

Frequency stability of emitter follower type crystal oscillators

AbstractRecently, crystal oscillators are used increasingly with the advances of electronic components. Particularly, the adjustmentfree crystal oscillators with only a few circuit elements are used widely since they are suited for IC's. Hence, stabilization of their frequency is very important. In this paper, the simplest emitter follower type crystal oscillator made of a transistor, a quartz crystal, a capacitor, and three resistors is studied in terms of its frequency stability. From the calculations and experiments, the following results have been obtained.The oscillation frequency is more stable against the change of an external capacitance if larger values are chosen for the collector capacitance CC, the grounded base current gain α, and the α cutoff frequency fα. Against the change of the power supply voltage, the optimum value of fα can be determined after CC is selected from the forementioned condition. The oscillation frequency deviation is smaller for a larger equivalent inductance L1 regardless of the Q value of the crystal. Based on these results, it is found that the improvement is more than sixfold against the variation of the power supply voltage, and more than elevenfold against that of the circuit capacitance.

Estimation of the effect of oscillator instabilities on signal processing by means of Monte Carlo computer simulation

In this paper, Monte Carlo computer simulation is used to estimate the effect of oscillator instabilities on signal processing. The key link of this method is generating high quality random number sequence simulating the phase noise of the oscillator. The case of the pulse compression performance is discussed as an example in order to clarify: (1) the effect of oscillator instabilities on pulce compression performance, and (2) the requirement of oscillator frequency stability when the tolerance of the system performance is known. Finally, some computer simulation examples are given which will provide as reference data for engineering designers.

Elementary deterministic theories of frequency and amplitude stability in feedback oscillators

First, the linear theory of frequency stability when applied to nearly sinusoidal feedback oscillators is critically reviewed. In this respect, a definition of the so-called linear oscillator is clarified. Then, the describing-function method and the Chua and Tang approach are applied to obtain new expressions for the oscillation-frequency and oscillation-amplitude stability of feedback oscillators considered as nonlinear networks.

Stabilization of UHF oscillator frequency by use of an auxiliary resonator

The current interest in the frequency stabilization of uhf oscillators is directed toward the implementation of gyrotrons in active plasma diagnostics. Toward this end this paper demonstrates a method which permits consideration in general form of the effect of electron frequency shift on the frequency stability of uhf oscillators using an auxiliary high-Q resonator. The method is used to determine the parameters of a gyrotron model optimized from the viewpoint of frequency stabilization.

Contribution to the linear theory of frequency stability of RC oscillators

In this paper, the frequency stability problem in RC oscillators is considered. General expressions describing variations of the real and imaginary parts of the characteristic equation roots, caused by variations in network elements' parameters, are developed. The superiority of our approach over the previously presented ones is that it allows to describe not only slow variations (long-term stability) but also fast variations (short-term stability) of oscillation frequency. It is shown that the so-called frequency stability factor S_F can be a reasonable criterion of frequency stability only for some types of RC oscillators. In this context, oscillators with the selective feedback path being of bandpass or bandreject type and with some additional resistive feedback path of the maintaining amplifier are discussed in detail.

Single longitudinal mode operation of long, integrated passive cavity InGaAsP lasers

We propose a new 1.3-μm wavelength InGaAsP laser—the integrated passive cavity (IPC) laser—and demonstrate its device performances compared with conventional lasers fabricated under similar procedures. The long IPC laser (3.55-mm-long passive cavity), as well as the short IPC laser, exhibited single frequency oscillation even just above the threshold, and the maximum ratio of longitudinal main to submode exceeded 30 dB. They also showed favorable effects in the oscillation frequency stabilization.

Short-Term Frequency Stability of Relaxation Crystal Oscillators

Due to the need for stable frequency rectangular wave signals, various relaxation quartz crystal oscillators were designed. Therefore it is of interest to have data on their short-term frequency stability. The generally accepted definitions of measures for short-term frequency stability and measurement procedures are reviewed in this paper. Measurement results for the short-term frequency stability of quartz crystal multivibrators in time and frequency domains show a high spectral purity of the multivibrator output signal. The single-sideband-to-carrier phase noise has values lower than -90 and -120 dB on the offset frequencies of 1 and 10 Hz, respectively. The white phase noise is about -160 dB. The power law spectral density model of fractional frequency fluctuations for the quartz multivibrators is established and a discussion on the noise sources is given.

Experimental Properties of Three-Cavity Tunnel Diode RF Oscillators

The properties of an oscillator-frequency stabilization scheme involving a system of three resonators used in conjunction with a tunnel diode as an active element are discussed. A theoretical description of the behavior of the oscillator is given, together with a procedure which allows one to verify the validity of the theoretical model. It is found that as the oscillator is tuned over the operating frequency range, two sets of hysteretic frequency jumps are observed, the measured position of which should completely characterize the stabilization system's parameters. Results of the frequency stability measurements on a prototype of the three-cavity oscillator are also presented which experimentally agree with the predicted stabilization properties of the system.

Subharmonic Sampling for the Measurement of Short-Term Stability of Microwave Oscillators

The use of digital techniques for the precise measurement of medium- and short-term frequency stability of oscillators requires good resolution of the frequency counter. In the case of microwave oscillators, this is often preceded by some form of down-conversion. This paper is concerned with the theoretical principles, description, operation, and performance of a down-conversion system based on the subharmonic sampling technique. The system is intended for use on microwave oscillators with good frequency-stability performance and has as main features the use of a single frequency-stable reference oscillator and a pulse generator-sampler which allows power optimization of the subharmonic selected. The complete experimental system is presented and the limitations are discussed.

Temperature Stabilization of GaAs MESFET Oscillators Using Dielectric Resonators

A simple model of the temperature stabilization of dielectric resonator FET oscillators (DRO's) is presented. Deduced from the oscillation condition, the model furnishes relations for oscillation power and frequency stability with temperature. A stack resonator with an appropriate linear resonance frequency/temperature characteristic has been developed and used to stabilize a DRO: frequency stability of +- 120 kHz over - 20°C to 80°C (/sup delta=/+- 0.1 ppm/K) at 11.5 GHz has been achieved.

Oscillation center frequency tuning, quantum FM noise, and direct frequency characteristics in external grating loaded semiconductor lasers

Simple analytical expressions for the oscillation frequency, quantum FM noise spectrum, oscillation power spectrum, spectral linewidth, and direct optical frequency modulation efficiency in semiconductor lasers with external grating feedback are presented. Experimental results for the grating loaded AlGaAs lasers are in good agreement with the theoretical predictions. Remarkable reduction in spectral linewidth to less than 50 kHz is achieved by feeding back only 10-3of the output power. Oscillation frequency stabilization, frequency jump behavior, and reduction in direct optical frequency modulation efficiency are also discussed.