A simplified approach to optimum noise source impedance determination for GaAs FET amplifiers

A simple, analytical approach to determine the optimum noise source impedance of a GaAs FET amplifier in the 3-12 GHz frequency range is developed. The procedure can also be used in the 0-5—3 GHz range, but the model on which the procedure is based may be less accurate in this frequency range. The approach requires knowledge of the transistor's small-signal model parameters and its minimum noise temperature versus frequency. The approach is relatively insensitive to errors in the value of the GaAs FET small-signal parameters, but noise in the required minimum noise temperature data is potentially a source of nonlinear errors in the computed value of the optimum noise source impedance with respect to the error in the minimum noise temperature data The amount of error in the computed value of optimum noise source resistance is roughly proportional to the error in the minimum noise temperature data when the error at each data point is correlated, while the error in the computed value of the optimum noise source reactance is roughly three times the error present in the minimum noise temperature data. When the error is uncorrelated, the method does not yield acceptable results.     

An improved model for noise characterization of microwave GaAs FETs

A broadband noise model for microwave FETs has been described. The model consists of small-signal lumped elements together with two noise sources. A measurement of broadband S parameters plus a single-frequency measurement of optimum source susceptance can yield enough information to determine the model, although greater accuracy is obtained using additional noise data to determine the precise value of the gate resistance. The model's predictions match well with measured noise parameter data for a high-performance GaAs FET over a wide frequency range     

Determining intrinsic noise parameters of 0.25 mu m gate pseudomorphic HEMT

An accurate equivalent circuit of a pseudomorphic HEMT (PM-HEMT) has been used, together with physically realistic values for the intrinsic PM-HEMT noise parameters (P, R, and C) to estimate the extrinsic noise parameters (minimum noise figure, optimum noise impedance, etc.) of a 0.25 mu m gate PM-HEMT. It is demonstrated that good agreement with experiment can be obtained for the minimum noise figure, optimum noise impedance, and also noise resistance, over the frequency range 6-18 GHz.<>     

The noise performance of microwave transistors

Expressions for the noise parameters of microwave transistors are derived. The theory is based on a small-signal common-emitter equivalent circuit which includes a new basic noise equivalent circuit and the dominanting header parasitics. The theory is verified experimentally in the L-band (1 to 2 Gc/s) frequency range using Ge and Si microwave transistors. It is found that the header parasitics have little influence on the minimum noise figure, but do have large effects on the equivalent noise resistance and the optimum source admittance in the frequency region above about one-half of the series-resonant frequency resulting from the parasitics in conjunction with wafer parameters. For a quick evaluation of the noise performance, new approximate expressions are also given for the noise figure and for the optimum current which produces the lowest value.     

A functional GaAs FET noise model

It is the purpose of this paper to develop a theory upon which the design of low noise FET amplifiers can be based. This is not a fundamenta model of the noise mechanisms in GaAs FET's, but rather, an endeavor to relate physically measurable device capacitances and resistances to the device noise figure and optimum noise source impedance. I will be shown that the noise performance of an FET can be adequately described by two uncorrelated noise sources. One, at the input of the FET, is the thermal noise generated in the various resis, tances in the gate-source loop. This noise source is frequency dependent and it can be calculated from the equivalent circuit of the FET. The second noise source, in the Output of the FET, is frequency independent, and not recognizably related to any measured parameters. This output nise is a function of drain current and voltage. The decomposition of the FET noise into two uncorrelated sources simplifies the design of broad-band low noise amplifiers. Once the equivalent circuit of a device and its noise figure at one frequency are known, the optimum noise source impedance and noise figure over a broad range of frequencies may be calculated. For the device designer this model also may be helpful in balancing input-output noise tradeoffs.     

Analytical noise model with the influence of shot noise induced bythe gate leakage current for submicrometer gate-lengthhigh-electron-mobility transistors

A new high-frequency noise model which takes into account the influence of shot noise induced by the gate leakage current is introduced; the model accurately explains the observed minimum noise figure of submicrometer gate-length HEMT's as a function of frequency. Based on the steady-state Nyquist theorem for multiterminal devices recently reported, the minimum noise figure and the corresponding optimum source impedance of the microwave field effect transistors are expressed as functions of the measurable device parameters including noise spectral intensities and small-signal circuit parameters. The derived minimum noise figure can be shown to reduce to a simple form, i.e., an empirical relation with two fitting constant. The simple form and the derived formulas for the optimum source impedance can explain very well the experimental findings of the submicrometer gate-length high electron mobility transistors over the extended microwave frequency range and also provide the informations needed for the design of microwave low noise amplifiers     

Modeling of noise parameters of MESFETs and MODFETs and theirfrequency and temperature dependence

A simple noise model of a microwave MESFET (MODFET, HEMT, etc.) is described and verified at room and cryogenic temperatures. Closed-form expressions for the minimum noise temperature, the optimum generator impedance, the noise conductance, and the generator-impedance-minimizing noise measure are given in terms of the frequency, the elements of a FET equivalent circuit, and the equivalent temperatures of intrinsic gate resistance and drain conductance to be determined from noise measurements. These equivalent temperatures are demonstrated in the case of a Fujitsu FHR01FH MODFET to be independent of frequency in the frequency range in which 1/f noise is negligible. Thus, the model allows prediction of noise parameters for a broad frequency range from a single frequency noise parameter measurement. The relationships between this approach and other relevant studies are established     

Diagnosis and reduction of conducted noise emissions

A systematic method for the diagnosis and reduction of conducted noise emissions is described. The method consists of a device for determining whether the differential- or common-mode component of conducted noise is dominant along with a simplified equivalent circuit of the power supply filter for each component. The procedure consists of first using the device to determine which noise-component is dominant in a particular frequency range and then using the simplified equivalent circuits to determine whether an anticipated change in value of an element in the power supply filter will be effective     

A NOVEL Ku-BAND LOW NOISE AMPLIFIER WITH HEMT AND GaAs MMIC

A novel Ku-band low noise amplifier with a high electron mobility transistor (HEMT)and a GaAs monolithic microwave integrated circuit (MMIC) has been demonstrated. Its noisefigure is less-than 1.9dB with an associated gain larger than 27dB and an input/output VSWRless than 1.4 in the frequency range of 11.7-12.2GHz. The HEMT and the microwave series in-ductance feedback technique are used in the first stage of the amplifier, and a Ku-band MMIC isemployed in the last stage. The key to this design is to achieve an optimum noise match and a min-imum input VSWR matching simultaneously by using the microwave series inductance feedbackmethod. The B J-120 waveguides are used in both input and output of the amplifier.     

零偏置光电振荡器相位噪声的讨论与分析

光电振荡器(OEO)可以产生低相位噪声的微波信号。在OEO中,MZ调制器(MZM)可以偏置于正交工作点使基频信号的损耗最低,也可以工作于零偏置点从而得到倍频信号。在MZM零偏置的OEO中,利用电分频器将倍频信号分频得到基频信号,从而构建环路振荡器。本文对这2种OEO(MZM正交偏置和MZM零偏置)的相位噪声进行了理论分析。由理论分析可知,MZM零偏置OEO的相位噪声优于MZM正交偏置OEO。根据仿真结果,可以发现MZM零偏置OEO的相位噪声噪底比MZM正交偏置OEO的相位噪声低3 dB。另外,MZM零偏置OEO的振荡模式间隔并不会受到电分频器的影响。     

Influence of burst noise on noise spectra

A method of calculating the spectrum of multilevel burst noise has been given. Measured noise spectra of bipolar transistors with burst noise together with calculated characteristics have been presented. A comparison of the measured and calculated characteristics shows that burst noise is responsible for the noise spectrum deviations in the low frequency range. In the Appendix a practical method of burst noise spectral density calculation has been given.     

On the noise performance of bipolar transistors in untuned amplifiers

From a generalized approach this paper reexamines the noise performance of bipolar transistors in untuned amplifiers. New results are obtained for the upper corner frequency which fully characterize the frequency dependent noise figure curves under conditions of arbitrary and optimum source conductance termination. The effects of the collector bias current on the minimum noise figure, the optimum source conductance and the upper noise corner frequency are presented both analytically and graphically. The results also include the effects of source capacitance on noise figures. A systematic design of low-noise untuned low-pass amplifiers with desired gain-bandwidth performance can be readily achieved with the help of the results presented.     

Designing FET's for broad noise circles

It is shown that the keys to broader noise circles are a lower minimum noise figure and a small optimum generator reflector coefficient. An optimum FET width for the smallest generator reflection coefficient and the broadest noise circles has been demonstrated with 0.25 μm MODFETs. A FET of optimum width also has the lowest noise figure with a 50 Ω generator. An expression is derived showing that the optimum gate width is inversely proportional to frequency, and that the optimum width should be a weak function of gate length for FETs optimally scaled for gate length     

HEMT for low noise microwaves: CAD oriented modeling

By means of an automatic measuring system which allows the rapid and accurate characterization of microwave transistors in terms of noise and scattering parameters simultaneously, 32 HEMTs of four manufacturers have been tested. From the experimental data so obtained the equivalent circuit of the `typical' device which represents each transistor set has been extracted using a decomposition technique. This procedure allows the optimum fitting of the global performance by exploiting the correlation between the model elements and the measured parameters over the operating frequency range. Since the method takes into account also the noise behavior of several devices of each series, a substantial improvement of the model performance for use in (M)MIC CAD of low-noise amplifiers is obtained     

低温背景下红外焦平面阵列的噪声分析

对红外探测器在低温背景下的噪声模型及特性进行了分析与实验研究。利用探测器噪声四参数法计算模型与方法;搭建实验平台对红外探测器在不同低温背景温度下的性能进行测试,得到红外探测器的低频时间噪声,高频时间噪声,低频空间噪声各自与温度、积分时间的关系。实验表明:在一定温度区间内,低频时间噪声表现出较强的温度相关性,低频空间噪声表现出较明显非线性响应特性,高频空间噪声表现出积分时间相关性。     

On the theory of 1/f noise of semi-insulating materials

The 1/f noise phenomena associated with devices involving semi-insulating materials, for instance GaAs MESFET's on semi-insulating GaAs, has long been a perplexing problem. In this particular case the 1/f noise corner frequency can be up to 100 MHz before the mean square noise current at the drain is dominated by the Nyquist noise associated with the channel conductance. No reasonable explanation has ever been given, although there are many different theories. 1/f noise is a common phenomena in nature and other devices involving semi-insulating materials. We propose here that this 1/f noise is a bulk phenomena associated with localized high frequency variations and long range low frequency fluctuations, the lowest frequency being limited only by the volume of the material. Specifically the proposal here is that injection of a current I into a semi-insulating material will result in a mean square noise voltage at the point of injection given by v/sub n//sup 2/~=2(kT/q)q/spl Delta/fR(/spl omega//sub c///spl omega/) Volts/sup 2/ where /spl omega//sub c/=1/t/sub t/, for the radian frequencies, /spl omega/, larger than /spl omega//sub c/ which is the reciprocal of the transit time of the carriers. For a long sample and long transit times then this 1/f noise voltage due to current injection will be larger than the Nyquist mean square noise of the sample alone as long as the DC voltage developed across the semi-insulating sample exceeds ((2kT/q)l/sup 2/(/spl omega///spl mu/))/sup 1/2/. This theory then gives the 1/f or 1//spl omega/ frequency dependence. The dc current I might be injected for instance by the substrate current in a GaAs MESFET being injected into the semi-insulating substrate, or gate current in an IGET being injected into the gate insulator.<>     

FM noise and spectral linewidth reduction by incoherent opticalnegative feedback

An all-optical, stable, external feedback method, the incoherent optical negative feedback method, is proposed and demonstrated for spectral linewidth reduction and optical-frequency stabilization of distributed-feedback (DFB) lasers. The power-spectral density of frequency modulation (FM) noise is shown to be reduced in a wide range of up to several hundreds of megahertz. The linewidth and the optical-frequency drift are simultaneously experimentally reduced to about 140 kHz and less than 17 MHz, respectively. The frequency range of the effective FM noise reduction and the reduction ratio of the FM noise are up to 1 GHz and 22 dB, respectively     

Intensity noise in long-wavelength superluminescent sources

Noise in broadband 1.3-μm superluminescent diodes (SLDs) is investigated experimentally, using a balanced detector arrangement to determine the excess noise factor as a function of photodetector current. Measurements were made in both the low-frequency 1/f, regime (<500 kHz) and the high-frequency quantum noise spectral region. The data at higher frequencies are in agreement with predictions of the quantum amplifier model, with values of the spontaneous emission coupling factors ranging from 1.2 to 1.9. It is also found that noise for one polarization of the light is uncorrelated with the noise for the orthogonal polarization over the 0-1 MHz frequency range. This implies that the 1/f, noise is not related to carrier density (gain) fluctuations in the active region of the device. An integrated optic chip design to compensate for the excess intensity noise in fiber gyroscopes is proposed     

一种超宽带超低相位噪声频率综合器

为了解决直接频率合成方法频带拓展困难和锁相频率合成方法相位噪声附加恶化严重的问题,设计了一种联合直接模拟频率合成和锁相频率合成的混频锁相频率综合器.该频率综合器采用梳谱发生器激励超低相位噪声的偏移信号后,再将该信号插入锁相环进行环内混频,降低鉴相器的倍频次数进而优化输出信号的相位噪声,同时解决了超宽带混频锁相环的错锁问...     

Nonlinear adaptive noise compensation in electrogastrograms recorded from healthy dogs

Adaptive noise compensation is a popular method for improving signal-to-noise ratio in a variety of biomedical applications with its major disadvantage being the requirement for a reference channel containing noise strongly correlated to the noise in the primary channel. In many biomedical applications the utilization of a channel containing such noise without any representation of the information signal is difficult if not impossible. In this study we investigated the possibility of applying adaptive compensation in nonideal noise environments containing substantial presence of information signal in the reference channel. The signal in the reference channel was subjected to nonlinear manipulations for reducing the signal-to-noise ratio, thus diminishing the representation of information signal. The methodology was tested on canine electrogastrographic (EGG) signals of four unconscious dogs which underwent laparotomy and implantation of six pairs internal stainless steel electrodes in addition to the eight-channel abdominal EGG. Fourteen-channel (six internal and eight cutaneous) were obtained from each dog for 1/2 h. The signals were digitized and processed by computer. All internal signals showed regular and coupled gastric electrical activity with frequency of repetition in the normogastric range [3-9 cycles-per-minute (cpm)]. A single pair of primary and reference channels was selected from each cutaneous recording and exponential manipulators in the reference channels were introduced. The manipulators were tuned to maximize the percent distribution of spectral components in the canine normogastric range of each frequency spectrum calculated from the signal at the output of the adaptive compensator. Significant increment in the percent distributions in the normogastric range (p < 0.01) was noted after tuning the exponential manipulator, and in many frequency spectra the recovery of the genuine dominant frequency peak of gastric electrical activity as determined by the internal recordings was noted. This study indicated that low percent distributions registered by some EGG channels are related to external nonlinear factors, the impact of which can be partially compensated.