高速高精度A／D转换器结构浅析

全并行(闪烁型)A/D转换器和逐次逼近型A/D转换器不能同时达到很高的转换速度和分辨率。本文介绍了几种能同时实现高速高分辨率A/D转换的电路,并对二步式A/D转换器、分区式A/D转换器以及流水线型A/D转换器的基本原理、结构和误差作了一些分析。     

12位1O MS/s CMOS流水线A/D转换器的设计

文中介绍了一种六级12位10Msample/sCMOS流水线A／D转换器的设计。该设计方案采用了双差分动态比较器结构,保证了处理模拟信号的精度与速度;采用冗余编码技术,进行数字误差校正,减小了多种误差敏感性,避免了由于余量电压超限而导致的失码,并降低了采样／保持电路和D/A转换电路的设计难度。     

基于OrCAD/PSpice的AD/DA转换电路的仿真实验研究

分析了A/D D/A转换器的内部结构及其工作原理,并利用OrCAD/PSpice软件所提供的脉冲信号源及瞬态分析功能,解决了以往受传统实验仪器设备限制而难以验证的问题。结合OrCAD/PSpice软件分别对D/A转换电路、A/D转换电路与及由A/D D/A组成的转换电路进行瞬态分析与仿真。仿真结果表明所设计电路的仿真波形与理论值一致,当数字信号的转换位数越多,则转换误差越小。     

一种基于符号动力学的新颖混沌A/D转换器的设计

本文分析了基于动力学系统的混沌A/D转换器的工作原理。提出了一种新的混沌映射方程,利用一种新颖的误差自补偿的方法,消除了混沌A/D转换过程中的迭代误差,提高了A/D转换的精度,此外,本文实现了信号放大与A/D转换的一体化设计。运用PSPICE对电路进行了仿真,结果表明该电路满足了A/D转换器的转换速度与转换精度的要求。为混沌A/D转换器的研究作了进一步的探索。     

用于带数字校正12位40MS／s流水线ADC的MDAC电路及数模接口

设计了一个用于40 MHz采样率,12位精度流水线A/D转换器第一级的MDAC电路.该电路采用高增益带宽积的增益自举放大器,在3.5 pF负载电容下,可以在8 ns内稳定在最终值的0.01%;设计了低失调、低回踢噪声比较器.蒙特卡罗分析表明,失调电压小于7 mV.电路采用SMIC 0.35 μm/3.3 V CMOS工艺,用于一个带数字校正的流水线A/D转换器.在MDAC中加入一个D/A接口电路,可以在不引入过多模拟电路的前提下,配合数字校正部分完成其校正功能.     

高精度高速A／D转换器时钟稳定电路设计

对高速A/D转换器（ADC）的结构及其时钟稳定电路的设计概念，研究对象进行了介绍，并对用于高速A/D转换器的时钟稳定电路进行了调研，从而提出了一种新的设计方法。     

过取样A／D或D／A变换技术

过取样A/D、D/A变换(oversampled A/D、D/A converter)作为一种电路设计技术,已经迎来了一个新的发展时期,该技术使用了Δ调制和ΔΣ调制电路,以低成本实现了具有线性变换特性、高精度、高分辨率的A/D、D/A变换,增加了DSP的比重,减轻了模拟电路的负担,适应了VLSI的发展要求。     

过采样模／数转换器的模拟与测试

通常采用诸如峰值误差、积分非线性度或微分非线性度等参数来表征模-数转换器的性能。然而,这些参数已不能用来表征采用反馈和过采样结构的转换器的性能。本文提出了表征A/D转换器的线性,非线性和统计特性的另一些参数,并提出了一种新方法(称为正弦最小误差法)来估计这些参数的数值。所提出的方法同样适用计算机模拟或对试验测量实际电路的方法来分析A/D转换器的性能。     

一种适用于快速高分辨率A／D和D／A转换器的自校准方法

单片A/D和D/A转换器存在着受现有电路元件的有限精度限制的缺点。一种新的自校准方法使得对广泛用于高速转换器的二元加权电流源阵列的线性误差进行校正成为可能。为了得到高的校准精度,使用了一种改进的双斜率法(modified dual-slope method)。这就使得制造具有14位或更高分辨率、转换时间小于15μs的A/D和D/A转换器成为可能。     

16位逐次逼近A/D转换器熔丝误差修调技术

提出了一种提高16位逐次逼近(SAR)A/D转换器精度的熔丝误差修调技术。该技术用于提高A/D转换器内部核心模块—16位DAC的精度,从而达到提高整个A/D转换器精度的目的。电路采用标准CMOS工艺流片。测试结果显示,熔丝误差修调后,常温下,电路的INL为2.5 LSB,SNR为88.8 dB,零点误差EZ为1.1 LSB;修调后,A/D转换器有效位数ENOB从12.56位提高到14.46位。     

Performance improvement in tensile-strained In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As metamorphic HEMT

This paper proposes a In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As (x=0.3-0.5-0.3) metamorphic high-electron mobility transistor with tensile-strained channel. The tensile-strained channel structure exhibits significant improvements in dc and RF characteristics, including extrinsic transconductance, current driving capability, thermal stability, unity-gain cutoff frequency, maximum oscillation frequency, output power, power gain, and power added efficiency.     

Very low-noise Al/sub 0.3/Ga/sub 0.7/As/Ga/sub 0.65/In/sub 0.35/As/GaAs single quantum-well pseudomorphic HEMTs

AlGaAs/GaInAs/GaAs pseudomorphic HEMTs with an InAs mole fraction as high as 35% in the channel has been successfully fabricated. The device exhibits a maximum extrinsic transconductance of 700 mS/mm. At 18 GHz, a minimum noise figure of 0.55 dB with 15.0 dB associated gain was measured. At 60 GHz, a minimum noise figure as low as 1.6 dB with 7.6 dB associated gain was also obtained. This is the best noise performance yet reported for GaAs-based HEMTs.<>     

A 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode array

We report a 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode (APD) array. The mean breakdown voltage of the APD was 57.9 V and the standard deviation was less than 0.1 V. The mean dark current was /spl sim/2 and /spl sim/300 nA, and the standard deviation was /spl sim/0.19 and /spl sim/60 nA at unity gain (V/sub bias/ = 13.5 V) and at 90% of the breakdown voltage, respectively. External quantum efficiency was above 40% in the wavelength range from 1.0 to 1.6 /spl mu/m. It was /spl sim/57% and /spl sim/45% at 1.3 and 1.55 /spl mu/m, respectively. A bandwidth of 13 GHz was achieved at low gain.     

Al/sub 0.3/Ga/sub 0.7/As/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) doped-channel field-effect transistors (DCFET's)

The properties of both lattice-matched and strained doped-channel field-effect transistors (DCFET's) have been investigated in AlGaAs/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) heterostructures with various indium mole fractions. Through electrical characterization of grown layers in conjunction with the dc and microwave device characteristics, we observed that the introduction of a 150-/spl Aring/ thick strained In/sub 0.15/Ga/sub 0.85/As channel can enhance device performance, compared to the lattice-matched one. However, a degradation of device performance was observed for larger indium mole fractions, up to x=0.25, which is associated with strain relaxation in this highly strained channel. DCFET's also preserved a more reliable performance after biased-stress testings.<>     

Morphological and electrical characterization of SixCryCzBv thin films

Si_xCr_yC_zB_v thin films with several compositions have been studied for integration of high precision resistors in 0.8 μm BICMOS technology. These resistors, integrated in the back-end of line, have the advantage to provide high level of integration and attractive electrical behavior in temperature, for analog devices. The film morphology and the structure have been investigated through transmission electron microscopy analysis and have been then related to the electrical properties on the base of the percolation theory. According to this theory, and in agreement with experimental results, negative thermal coefficient of resistance (TCR) has been obtained for samples with low Cr content, corresponding to a crystalline volume fraction below the percolation threshold.Samples with higher Cr content exhibit, instead, a variation of the TCR as a function of film thickness: negative TCR values are obtained for thickness lower than 5 nm, corresponding to a crystalline volume fraction below the percolation threshold; positive TCR are obtained for larger thickness, indicating the establishment of a continuous conductive path between the Cr rich grains. This property seems to be determinant in order to assure the possibility to obtain thin film resistors almost independent on the temperature.     

Highly linear Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMTs

We report an Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMT with enhanced linearity. By engineering the channel region, i.e., inserting a 6-nm-thick AlGaN layer with 5% Al composition in the channel region, a composite-channel HEMT was demonstrated. Transconductance and cutoff frequencies of a 1 /spl times/100 /spl mu/m HEMT are kept near their peak values throughout the low- and high-current operating levels, a desirable feature for linear power amplifiers. The composite-channel HEMT exhibits a peak transconductance of 150 mS/mm, a peak current gain cutoff frequency (f/sub T/) of 12 GHz and a peak power gain cutoff frequency (f/sub max/) of 30 GHz. For devices grown on sapphire substrate, maximum power density of 3.38 W/mm, power-added efficiency of 45% are obtained at 2 GHz. The output third-order intercept point (OIP3) is 33.2 dBm from two-tone measurement at 2 GHz.     

Comparison between Pt/TiO2/Pt and Pt/TaOX/TaOY/Pt based bipolar resistive switching devices

Nonvolatile memories have emerged in recent years and have become a leading candidate towards replacing dynamic and static random-access memory devices. In this article, the performances of TiO₂ and TaO₂ nonvolatile memristive devices were compared and the factors that make TaO₂ memristive devices better than TiO₂ memristive devices were studied. TaO₂ memristive devices have shown better endurance performances (10⁸ times more switching cycles) and faster switching speed (5 times) than TiO₂ memristive devices. Electroforming of TaO₂ memristive devices requires~4.5 times less energy than TiO₂ memristive devices of a similar size. The retention period of TaO₂ memristive devices is expected to exceed 10 years with sufficient experimental evidence. In addition to comparing device performances, this article also explains the differences in physical device structure, switching mechanism, and resistance switching performances of TiO₂ and TaO₂ memristive devices. This article summarizes the reasons that give TaO₂ memristive devices the advantage over TiO₂ memristive devices, in terms of electroformation, switching speed, and endurance.     

Electrooptic ferroelectric Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films

We report on waveguiding and electrooptic properties of epitaxial Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films grown by radio-frequency magnetron sputtering on Al/sub 2/O/sub 3/(11_02) single crystal substrates. High optical waveguiding performance has been demonstrated in infrared and visible light. The in-plane electrooptic effect has been recorded in transmission using a transverse geometry. At dc fields, the effective linear electrooptic coefficient was determined to 28 pm/V, which is promising for modulator applications.     

A 1 cm/spl times/1 cm In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode array

We report a 1 cm/spl times/1 cm array of 100 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiodes (APD). The average breakdown voltage was 28.7 V with a standard deviation of less than 0.5 V. The distribution of breakdown voltage across the area followed a radial pattern consistent with a slight epitaxial growth nonuniformity. The mean dark current at a gain of 10, or 6.1 A/W, was 10.3 nA, and none of the 100 APDs had a dark current of more than 25 nA. The bandwidth at a gain of 10 was 6.2 GHz, and the maximum gain-bandwidth product was 140 GHz. This technology is ideally suited for next-generation three-dimensional imaging applications.