Punchthrough behavior in short channel NMOS and PMOS 6H-siliconcarbide transistors at elevated temperatures

An experimental investigation of the effects of high temperature on short channel NMOS and PMOS transistors in 6H-SiC is reported. Punchthrough characteristics are presented and examined at room temperature and 300°C. The punchthrough current increases dramatically for scaled PMOS transistors at high temperature while the temperature dependence of electrical characteristics for short channel NMOS is small. The results presented in this paper also provide insight into design criteria for short channel silicon carbide (SiC) devices intended for operation at elevated temperatures     

Experimental study of flicker noise in m.i.s. field-effect transistors

The experimental dependence of flicker noise on the geometry parameters of m.i.s. field-effect transistors is presented. It is found that the gate-referred r.m.s. noise voltage en in the flicker region is inversely proportional to the square root of the gate width of the device. It is also observed that en is directly proportional to the effective gate-insulator thickness. These experimental results are in good agreement with the published results of flicker-noise analyses. Thus, for a given surface State density, it is possible to reduce the magnitude of flicker noise by a control of device geometry parameters.     

Investigation of flicker noise and deep-levels in GaN/AlGaN transistors

We report flicker noise measurements combined with deep-level transient spectroscopy of the doped and undoped channel GaN/AlGaN heterostructure field-effect transistors. The low-temperature noise spectra for the doped devices show clear generation-recombination peaks. The value of the activation energy extracted from these noise peaks is consistent with the activation energies measured using deep-level spectroscopy. Our results indicate that the input-referred noise spectral density of the undoped channel devices is much smaller (up to two orders of magnitude) than that of the doped channel devices with comparable electric characteristics. The additional defects due to doping add up to the generation-recombination and flicker noise.     

A study of flicker noise in MOS transistors operated at room and liquid helium temperatures

A study of flicker noise in MOS transistors operated in the linear and non linear regions at room and liquid helium temperatures is proposed. Besides, a theoretical analysis of the drain current noise characteristics is developed in the framework of the mobility fluctuation model as well as of the carrier number fluctuation model. It is shown experimentally that a close correlation between the drain current spectral density and the transconductance squared dependencies with gate voltage (or drain current) and drain voltage is observed in our devices both at room and liquid helium temperatures. Therefore, it is concluded that the carrier number fluctuation model is not only applicable to MOS devices operated at room temperature but also at liquid helium temperature in ohmic and non ohmic regimes. In addition, peculiarities of the drain current noise related to the appearance of a kink effect at liquid helium temperature in the saturation current characteristics are also discussed.     

Accuracy of PSP and BSIM4 models in determination of IP3 compression point

A comparative benchmark of the linearity properties of two of the most popular compact transistor models (BSIM4 and PSP) for nanometre process technologies (45 nm) is presented. The determination of the IP3 compression point for a particular network configuration, which is often encountered in RF mixers, is used as a comparison vehicle. Parameters of both the PSP and BSIM4 models adopted in the comparison have been fitted to a leading-edge 45 nm RF technology. The benchmarks show that the BSIM4 model is unable to capture the IP3 compression point whereas the PSP model yields the expected behaviour, thus enabling the determination of the correct value of IIP3.     

Non-quasi-static models including all injection levels and DC, AC,and transient emitter crowding in bipolar transistors

Two-dimensional equivalent-circuit models for bipolar junction transistors are systematically derived by solving the continuity equations for DC, AC, and transient excitations. These models take into account carrier propagation delay, all injection levels, as well as exponential doping profiles. They include analytically DC, AC, and transient emitter crowding in a more detailed and accurate manner than previously available. Extensions of the models to accommodate arbitrarily doped and heavily doped quasi-neutral layers and to include energy-gap narrowing due to the electron-hole plasma present at high current density are described. The analysis leads to compact large- and small-signal equivalent-circuit lumped models, suitable for use in circuit simulators such as SPICE. The analytical solutions obtained reveal the two-dimensional distribution of the current and carrier densities in the intrinsic base layer and the onset of emitter crowding. They also provide information for the extraction of the intrinsic base resistance. Several assumptions made in the derivations are assessed by the computer program PISCES. The methods presented apply to both homojunction and heterojunction bipolar transistors     

Dependence of low frequency noise in SiGe heterojunction bipolar transistors on the dimensional and structural features of extrinsic regions

In this paper, the effects of different transistor design aspects on the noise behavior of SiGe heterojunction bipolar transistors have been investigated. Selectively implanted collector, although retards the base push-out, does not deteriorate the noise characteristics. Moreover, a higher dopant implant in the extrinsic base region intended for a smaller base resistance does not deteriorate the noise characteristics. While the interface between the SiGe epitaxial and polycrystalline layers does not have any detrimental impact, the emitter-poly overlap significantly influences both the DC and the noise characteristics. Smaller emitter-poly overlap results in an increased non-ideal base current at lower bias voltages and produces appreciable generation–recombination noise. For all the transistors, except for the ones with smaller emitter-poly overlap, the base current noise power spectral density shows a near quadratic dependence on the base current, where the noise is believed to originate mostly from the superposition of the generation–recombination noise in the intrinsic emitter–base junction. The base current noise power spectral density for the transistors with a smaller emitter-poly overlap shows a near linear dependence on the base current, which results from an increased contribution from the trap-assisted tunneling fluctuations of the minority carriers at the surface of the emitter–base junction.     

Tradeoff between 1/f noise and microwave performance in AlGaAs/GaAsheterojunction bipolar transistors

The 1/f noise characteristics and microwave gain of AlGaAs/GaAs heterojunction bipolar transistors (HBT's) have been investigated as a function of surface passivation ledge length. These measurements clearly demonstrate that the ledge length imposes a tradeoff between the 1/f noise and microwave power gain performance. Compared to a conventional unpassivated self-aligned HBT, HBT's with 0.4 and 1.1 μm ledge lengths improve the equivalent input base noise current spectral density at 100 Hz by as much as 2 dB and 6.5 dB, respectively; while degrading the maximum available gain at 18 GHz by 0.3 dB and 2.4 dB, respectively     

Investigation of impact ionization and flicker noise properties in indium aluminum arsenide/indium gallinum arsenide metamorphic high electron mobility transistors with various work function-gate metals

This study investigates the effect of impact ionization using Ir, Pt, Pd, Ti gate metals and the direct correlation between these high work function metals and low frequency noise (LFN) on an In_0.4Al_0.6As/In_0.4Ga_0.6As metamorphic high electron mobility transistor (MHEMT). The effect of impact ionization on DC, RF, and cryogenic LFN is systematically studied and discussed. Gate metals with high work functions are used to suppress the kink effect and gate leakage current. Experimental results suggest that the Ir gate MHEMT exhibits superior thermal stable properties in a strong electrical field at various temperatures, associated with high gain, high current, and excellent low-frequency noise performance.     

Experimental results on fast surface states and 1/f noise in m.o.s. transistors

Experimental results for 1/f noise in m.o.s. transistors with very low surface state densities are presented. A direct relation between noise and surface state density is found, extending previously published data.     

Estimating symbol error rate vs. carrier to noise in IQ modulatedsystems based on digitization of constellation and statistical models

Methods used to characterize the degradation of symbol error rate (SER) vs. carrier-to-noise ratio (C/N) performance of several different components of systems that broadcast digital video signals are presented. The techniques are based on repetitively sampling and then digitizing the IQ constellation at baseband. Mathematically different levels of noise calculated relative to the carrier are added to the digitized constellation. Examination of the resulting distributions of noise versus error thresholds allows the estimation of SER vs. C/N in the absence of any error correction in the receiver. The effects of IF bandwidth and transmit and receive filters are also taken into account. The estimated SER vs. C/N can be plotted and compared to the theoretical SER vs. C/N for the modulation format, IF bandwidth, and transmit and receive filters in the system under test     

H．264／AVC中的整数变换与DCT变换的比较

数字视频技术在通信和广播领域获得了日益广泛的应用,视频信息和多媒体信息在网络中的处理和传输成为当前我国信息化中的热点技术。运动图像专家组和视频编码专家组给出一种更好的标准,确定为MPEG-4标准的第十部分,即H.264/AVC。简述H.264的研究意义及DCT的原理。为了减少运算量,分析H.264中如何对宏块的整数变换,详述H.264的编码变换的方法,给出整数变换方法与传统的DCT的区别和联系,并给出H.264的整数变换方法的快速算法即蝶形算法,这与传统的DCT变换是不同的。     

ERS-1 scatterometer measurements. I. The relationship between radarcross section and buoy wind in two oceanic regions

Extensive European Remote Sensing Satellite (ERS-1) spacecraft scatterometer measurements were collocated within ±25 km of buoy measurements at midlatitudes and in the equatorial Pacific during 1992-1994. Two different directional functional forms for the geophysical model were fit to these measurements described by cross section maxima aligned and offset, with respect to the mean wind direction. The two models exhibit fits with similar residuals for each of three years in the equatorial region. Thus, neither of these two model functions can convincingly be identified as more accurate than the other unless additional factors are considered. Nevertheless, the offset model results in an average directional offset near 10° for each season during the three-year period; whereas, no such offset was inferred at midlatitudes. The cross section dependence on wind direction also exhibits another unexpected average property: a larger downwind compared to upwind cross section, A₁₀≈-0.25 dB in the equatorial Pacific. This characteristic could be caused by a concentration of the short Bragg waves on the backside of the long wave crests. Both of these unexpected characteristics are likely related to a dominant systematic swell traveling nearly perpendicular to the prevailing easterly winds across the equatorial Pacific Ocean. The possible cross section dependence on wind stress and wind speed is due to long waves when adjusting the buoy measurements to a common height are discussed     

MPEG-4、H．264、AVS编解码标准的比较及其在IPTV中的应用

本文对MPEG-4、H．264、AVS编解码标准进行了详细的介绍、分析和比较。并介绍了它们在IPTV中的应用。     

宽色域视频标准ITU-R BT.1361与IEC 61966-2-4的分析和比较

ITU-R BT.1361和IEC 61966-2-4(xvYCC)是关于宽色域视频系统的2个标准,它们扩展色域的方法不尽相同.以电视系统中广泛使用的彩条测试信号为例,分析了两者间的差异、计算了实际可用信号幅度范围并比较了它们的色域大小.结果表明,在与常规色域兼容传输情况下,2种标准虽均可扩展色域,但数值不够大,进一步研究扩展色域方法的空间仍较大.