Low-frequency 1/f noise and persistent transients in AlGaN-GaN HFETs

Persistent photoresponse transients and low-frequency 1/f noise were measured in barrier-controlled devices such as AlGaN-GaN heterostructure field-effect transistors (HFETs). The persistent transients and 1/f noise were observed in drain and gate currents. A model describing trapping in a barrier-controlled device introduced, and the appropriate transient evolution and the noise spectra developed. Excellent agreement was obtained between the experimental measurements and the predicted temporal response and noise spectra. Finally, the correlation between drain and gate 1/f noise was measured, confirming that the same noise source (fluctuation in surface potential) is responsible to both currents.     

Detection of known signals in 1/f fractal noise

Based on the whitening property of wavelet transformation for 1/f noise, this paper addresses the problem of detecting deterministic signals in the presence of 1/f fractal noise. The transfer function of whitening filter is provided as well as the condition for whitening. The receiver structure based on Karhunen-Loeve expansion and the decision rule are also given. Finally performance of the detector is analyzed.     

1/f noise

1/f noise is a nonstationary random process suitable for modeling evolutionary or developmental systems. It combines the strong influence of past events on the future and, hence somewhat predictable behavior, with the influence of random events. Nonstationary autocorrelation functions for 1/f noise are developed to demonstrate that its present behavior is equally correlated with both the recent and distant past. The minimum amount of memory for a system that exhibits 1/f noise is shown to be one state variable per decade of frequency. The system condenses its past history into the present values of its state variables, one of which represents an average over the most recent 1 unit of time, one for the last 10 time units, 100 units, 1000, 10000, and so on. Each such state variable has an equal influence on present behavior.     

Milling cutter breakage detection by the discretewavelet transform

The paper describes the use of cutting force to detect milling cutter breakage based onthe discrete wavelet transform. The discrete wavelet transform performs a multi-level signaldecomposition of the cutting force so that the cutter breakage features can be extracted. Millingcutter breakage can then be detected from the cutting force with or without the cutter breakagefeatures. Experimental results have indicated that milling cutter breakage can be successfullydetected even under different cutting conditions.     

1/f noise sources

This survey deals with 1/f noise in homogeneous semiconductor samples. A distinction is made between mobility noise and number noise. It is shown that there always is mobility noise with an α value with a magnitude in the order of 10^-4. Damaging the crystal has a strong influence on α, α may increase by orders of magnitude. Some theoretical models are briefly discussed none of them can explain all experimental results. The α values of several semiconductors are given. These values can be used in calculations of 1/f noise in devices     

Unified presentation of 1/f noise in electron devices: fundamental 1/f noise sources

1/f noise in semiconductors, semiconductor devices, and collision-free devices (like vacuum tubes) is presented from a unified point of view, using an extended version of the F.N. Hooge equation (Physica, vol. 83b, p.9, 1976), which is generalized to all collision-dominated systems involving mobility, diffusion, and cross-section fluctuations. It also applies to collision-free processes involving vacuum tubes, Schottky barrier diodes operating in the thermionic mode, and in devices such as p-i-n diodes in which collision processes are not the determining factor. A generalized schematic is given for expressing the noise spectrum S/sub 1/(f) in the external circuit in terms of distributed noise sources of the nonuniform devices in terms of alpha /sub H/, so the latter can be determined from the former. It is then found that the Hooge parameter. alpha /sub H/ introduced by this equation can be used as a general measure of the noisiness of a system or device. Several cases in which the noise does not obey the quantum 1/f noise theory are discussed. Measurements on many different devices are examined, and an attempt is made to correlate measured values of the Hooge parameter with the values calculated from P.H. Handel's quantum theory of 1/f noise (1975, 1980).<>     

Bipolar transistors with low 1/f noise

Bipolar transistors employing low concentration emitter diffusion were obtained which show no current gain fall-off at low current levels, as well as significantly reduced 1/f noise. These devices may favourably be applied in low noise amplifiers.     

Estimation of 1/f noise

Several models have emerged for describing 1/f^γ noise processes. Based on these, various techniques for estimating the properties of such processes have been developed. This paper provides theoretical analysis of a new wavelet-based approach which has the advantages of having low computational complexity and being able to handle the case where the 1/f^γ noise might be embedded in a further white-noise process. However, the analysis conducted here shows that these advantages are balanced by the fact that the wavelet-based scheme is only consistent for spectral exponents γ in the range γ∈(0, 1). This is in contradiction to the results suggested in previous empirical studies. When γ∈(0, 1) this paper also establishes that wavelet-based maximum-likelihood methods are asymptotically Gaussian and efficient. Finally, the asymptotic rate of mean-square convergence of the parameter estimates is established and is shown to slow as γ approaches one. Combined with a survey of non-wavelet-based methods, these new results give a perspective on the various tradeoffs to be considered when modeling and estimating 1/f^γ noise processes     

1/f noise in HgCdTe photodiodes

1/f noise in HgCdTe photodiodes has been attributed to a variety of sources, most of which are associated with some form of excess current. At DRS, we have measured the 1/f noise in vertically integrated (VIP) and high-density vertically integrated photodiodes (HDVIP), over a wide range of compositions and temperature, for strictly well-behaved diffusion current limited operation. It is found that (1) the 1/f noise current is directly dependent on dark current density; (2) material composition and temperature are irrelevant, except in as much as they determine the magnitude of the current density; (3) in high-quality diodes, the 1/f noise is independent of background flux; and (4) surface passivation is relevant. These observations have been compared to the 1/f noise theory of Schiebel, which uses McWhorter’s fluctuation of the surface charge tunneling model to modulate diode diffusion current. Agreement is obtained with Schiebel’s theory for realistic surface trap densities in the 10¹²/cm² range, which will obviously be characteristic of the passivation used. The relevance of this work relative to high operating temperature phtodiodes is discussed.     

1/f noise in multicarrier systems

The 1/f noise power produced by several r.f. carrier currents in a carbon resistor is shown to be proportional to the total r.f. power dissipated in the resistor. This confirms that the noise is not a consequence of resistance fluctuations.     

Simplified 1/f noise calculations

A new tool, called the equivalent number of decades ND/sub e/, is introduced to simplify the analysis of noise in circuits containing 1/f noise sources. ND/sub e/ is similar to the familiar concept of equivalent noise bandwidth for white sources. A simple expression for ND/sub e/ is derived for a single-pole lowpass filter and is shown to be approximately correct for Butterworth and Chebyshev filters as well.<>     

Variance of simulated 1/f noise

A recently introduced mathematical model supporting the observed high variance of variance of excess noise is extended to a process having a 1/f spectrum. The variance of variance found by simulation was even higher than that of a Gauss-Poisson square wave.     

Variance fluctuations of 1/f noise

The difference in behaviour between the variances of 1/f noise and of thermal noise is related to the differences in the ratios of fourth moment to the second moment of the distributions. This ratio is found experimentally to be significantly different in the two cases.     

Avalanche-induced 1/f noise in bipolar transistors

It has been proposed that degradation of low current hFE, as a result of avalanching the emitter-base junction of a bipolar transistor, can be attributed to an increase in surface recombination velocity within the emitter-base space-charge region. This work shows that 1/fnoise is also increased during avalanche and that this increase is consistent with a previously reported correlation between surface recombination velocity and 1/fnoise.     

The wavelet transform based processing means for 1/f noise in millimeter wave focal plane array

After briefly introducing the characteristics of 1/f noise in millimeter wave focal plane array detectors, the paper analyses the relation of wavelet transform and 1/f noise in detail, suggests the fashion of decorrelating 1/f noise using the wavelet transform and deduces the relative expressions. The results of computer simulation show good effectiveness.     

Origin of 1/f noise in bipolar transistors

In planar n-p-n transistors fabricated in IC technology, the dependence of 1/fnoise on the base current density jB, the base width WB, and the emitter area FEwas measured. The power spectrumS_{iB}(f)of the base current fluctuations iBcan be represented by the empirical relationS_{iB} = const. jmin{B}max{gamma} cdot Fmin{E}max{beta} cdot wmin{B}max{-1} cdot f^{-1}where1 leq gamma leq 2and β has been found to be 1.3 or 2. The results of measurements on gate-controlled devices indicate that 1/fnoise cannot be explained by McWhorter's surface model. Therefore, a new model is proposed which assumes resistance fluctuations in the base region as the cause of 1/fnoise in bipolar transistors. The model establishes the relation forS_{iB}(f)as well as the magnitude of the coefficients β and γ.     

Measurement of white and 1/f noise within burst noise

A measurement method is described which enables the separate measurement of the power spectra of the normal noise (white and l/f) superimposed on burst noise. With this method the power spectra of normal noise can be determined for each burst noise level. It is found that the clean burst noise and the superimposed normal noise are generated by statistically independent processes. The fact that burst noise devices have a higher 1/f noise power content than devices without burst noise indicates that there exists a common condition for the generation of burst noise and 1/f noise.     

1/f noise of continuous-wave semiconductor lasers

Using linearised rate equations, the intensity fluctuations in the output of c.w. d.h. GaAlAs-diode lasers have been calculated in the low-frequency range, where the flicker noise dominates. The theoretical results are compared with the optical-intensity fluctuations, which are obtained experimentally. Our measurements indicate that 1/f noise in lasers is mainly caused by 1/f noise from carrier transport in the bulk material and the contacts.