Flicker Frequency Noise Research Articles

10 GHz cryocooled sapphire oscillator with extremely low phase noise

The phase noise characterisation of two 10 GHz cryogenic sapphire oscillators exhibiting frequency stability higher than 3×10 -15 is reported. One of these oscillators developed for the deep space navigation ground stations of the European Space Agency, incorporates a closed cycle cryocooler as cold source. Near the carrier, the measured phase noise is limited by a flicker frequency noise: S ? (f)=-30log(f)-98 dBrad 2 /Hz.

Parametric studies of matched filters to enhance the signal-to-noise ratios of LC–MS–MS peaks

Chromatographic parameters of reference signals employed in matched filter methods have been studied using numerical experiments to improve the signal-to-noise (S/N) ratios of small liquid chromatography (LC) peaks obtained with electrospray tandem mass spectrometers (MS–MS). These parameters include the width, shape, and S/N ratios of chromatographic peaks used as the reference signal profiles. Our results show the effect of reference peak widths on improving the S/N ratio of chromatographic peaks; the influence of reference peak shapes is negligible. To verify simulation results, various reference signals, including analyte peaks of high concentration standards, internal standard peaks, and artificial Gaussian peaks of different widths, have been employed to enhance signal peaks on real liquid chromatography–tandem mass spectrometry (LC–MS–MS) chromatograms via matched filter methods. Our experimental results demonstrate that the S/N ratio enhancement of chromatographic peaks agree with the simulation predictions. These findings, therefore, suggest that regardless of peak shape, a well-smooth peak with a width close to that of the analyte peak is an adequate reference signal, when matched filter methods are used to improve LC–MS–MS chromatograms. Nevertheless, all methods processed LC–MS–MS peaks in this study do not achieve the ideal improvement ratios estimated with simulation results. We attribute this deficiency to spike-like noise, which have considerable low frequency components riding on LC–MS–MS chromatograms. Matched filtering, which works as a low-pass filter in the frequency domain, cannot effectively eliminate low frequency flicker noise contributed by these spikes. In addition, simple median filtering does not provide adequate improvement despite being able to smooth out most spikes in the chromatograms.

Valence-band tunneling induced low frequency noise in ultrathin oxide (15Å) n-type metal-oxide-semiconductor field effect transistors

Low frequency flicker noise in n-type metal-oxide-semiconductor field effect transistors (n-MOSFETs) with 15Å gate oxide is investigated. A noise generation mechanism resulting from valence band tunneling is proposed. In strong inversion condition, valence-band electron tunneling takes place and results in the splitting of electron and hole quasi-Fermi levels in the channel. The excess low frequency noise is attributed to electron and hole recombination at interface traps between the two quasi-Fermi levels. Random telegraph signal in a small area device is characterized to support our model.

Effects of phase noise spectral shape on the performance of dpsk systems for wireless applications

AbstractPhase noise could be the major source of performance degradation in low cost low bit‐rate digital systems operating in the millimeter wavelength band. A general model considers the phase noise as the sum of several components, namely a white phase noise, a white frequency noise and a flicker frequency noise. All these components are taken into account in the evaluation of error probability in a DPSK receiver and are compared in terms of performance degradation.

Limitation of the frequency stability by local oscillator phase noise: new investigations and natural improvements

In frequency standards in which the atoms have a continuous interaction with the probe signal, local oscillator phase noise may limit medium term frequency stability. This spurious effect cannot be suppressed whenever there Is any truncation in the spectrum of the resonator response. Nevertheless, a simultaneous processing of the probe signal, similar to that of the NIST, and of the resonator response (by means of an appropriate demodulation) makes it possible to reduce this limiting effect. Previously achieved with a square wave frequency modulation, this result is now extended to various frequency modulations. An uncontrolled distortion in the demodulation waveform may significantly degrade the performance. For the case of a square wave phase modulation, the limiting effect also exists, but it is smaller than for a frequency modulation. When the phase noise of the local oscillator is naturally "not flat", it is possible to easily reduce the spurious effect: using the quasi-static approximation, one can calculate various optimized demodulation waveforms and the corresponding improvements. For the simplest optimized demodulation (f (M), 3f(M)), theoretical predictions are experimentally confirmed for flicker phase noise and flicker frequency noise.

Dynamic flicker frequency modulation and noise instability of oscillators

Due to oscillator dynamics, slow flicker modulation causes fast frequency fluctuations. This second-order effect as well as the associated spectral densities, frequency variance, and spectral line shape are considered. Second-order oscillator theory is based on the analytic signal, which generalizes the averaging and other classical methods.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Impact of flicker noise and random-walk noise on a phase-locked loop with finite propagation delay

Approximate expressions for the phase-error variance due to the nonwhite frequency noise of optical sources are derived to analyze the performance of optical phase-locked loops (PLL's). The approximation incorporates the loop propagation delay, which is inevitable in actual systems. The obtained expressions are in simple form and yield only 3% maximum error. Using the obtained expressions, the influence of the flicker frequency noise and the random-walk frequency noise on the laser linewidth requirements are discussed. By examining semiconductor lasers that have been reported, it is found, quantitatively, that the flicker frequency noise does not affect the linewidth requirements, even in the presence of finite loop propagation delay. The obtained approximate expressions are used to examine low-white-frequency-noise optical sources, such as solid-state lasers, and to yield the allowable values of flicker frequency noise and random-walk frequency noise.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Novel method of estimation flicker frequency noise in lasers

A simple method is proposed for the precise measurement of flicker (1/f) frequency noise in lasers. The method is based on measurement of the Allan variance of beat signals produced by delayed self-heterodyning. A simple relation between measured variance and frequency-noise spectrum is derived analytically. Measurement on a 1.5- mu m semiconductor laser diode is presented. It is pointed out that since the method possesses the great advantage of insensitivity to optical power fluctuations, it can be widely used for precisely testing laser frequency quality.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The state of the art of flicker frequency noise in BAW and SAW quartz resonators

Experimental results of the last 15 years are reviewed. Noise properties of crystal filters and oscillators are reported, along with practical measurements. It is shown that the additional phase fluctuations are compensated by frequency fluctuations and vice versa. With the assistance of these theoretical results the flicker and white frequency noise coefficients, h(-1) and h(0), respectively, are plotted versus unloaded Q and carrier frequency f(0) for the measured and published crystal oscillator noise characteristics. The dependence of h(-1) approximately 10(-12.75) Q(2) (u) is verified.

Relaxation quartz oscillators with crystal placed in feedback loop: Analysis and design

Our purpose in this paper is to provide a complete theoretical analysis of relaxation quartz oscillators using integrated circuits as active elements and a crystal placed in feedback loop. The general theory of relaxation oscillations is a theoretical background for this analysis, which provides solutions for oscillating conditions, oscillation buildup and period, and a flicker-frequency noise level. The main results are the criteria for the design of an optimal quartz relaxation oscillator having high immunity to circuit and ambient parameter variations and a low phase noise level. The results are derived for oscillators using TTL gates, but they are of a general validity and can be easily modified for every circuit of this kind. The conclusions drawn are discussed and confirmed through experiments.

RF Spectrum of Thermal Noise and Frequency Stability of a Microwave Cavity-Oscillator

The spectral distribution of the themal noise within a microwave cavity equipped with an extemal feedback loop has been calculated and measured. An equivalent electrical model is established from which the noise spectral density can be calculated at any post in the system, The effect of the gain and phase of the loop on the spectral distribution is measured with a spectrum analyzer through a heterodyne technique and comparison with theoretical calculations shows good agreement. Also, the modified cavity Q and resonant frequency is measured for various loop parameters. An experimental setup allowing precise measurement of frequency stability and FM noise close to carrier of microwave oscillators is presented and discussed. preliminary measurements of the short-term frequency stability of the system when operated as a microwave cavity-oscillator show a predominant flicker frequency noise. The measured FM noise close to carrier is related to time-domain measurements of frequency stabitity and to RF spectrum of the cavity-oscillator.

A model for flicker frequency noise of oscillators

A stationary statistical model is proposed for oscillator frequency fluctuations, leading to a flicker power spectral density for frequency fluctuations and to the corresponding time domain frequency instability (logarithmic behavior).