Extracting MOS parameter variations using dual-drain MOSFET offset

We have developed two offset models for dual-drain MOSFETs-one for surface-channel and one for buried-channel MOSFETs. By fitting the models to offsets measured at selected biases, estimates of various MOS parameter variations can be extracted. The models are originally intended to demonstrate that, contrary to current belief, channel implant variations can contribute as much offset to magnetic sensor MOSFETs as mobility variations. The utility of the method, however, extends beyond magnetic sensors. The same approach can be used to extract MOS parameter variations important in circuits such as MOS differential pairs     

幅度与相位分步识别的QAM调制模式识别算法

正交幅度调制(Quadrature Amplitude Modulation,QAM)信号的调制模式识别一直以来是人们研究的热点,通过星座图来进行调制模式识别也是一种常见的方法。然而,大多数调制模式识别算法会受到频偏和相偏的干扰,因此提出了一种幅度相位分步识别的QAM识别算法来识别调制模式。先利用卷积神经网络(Convolutional Neural Networks,CNN)识别出未消除频偏相偏的QAM星座图的幅度层数,对信号进行第一次分类;再检测每个信号点的瞬时相位进行差分,得到每个点之间的相位跳变幅度;经过减法聚类确定相位跳变次数,由此对信号在相位上进行二次分类,最后识别出QAM信号的调制模式。该方法虽然步骤比传统方法繁琐,但是不依赖于信号的频偏消除和相偏消除,能够起到很好的抗频偏作用。此外,因为没有频偏消除和相偏消除的步骤,所以使得信号不至于在频偏消除和相偏消除等预处理过程中损失信息量。经过试验,这种方法在识别率上比传统的神经网络识别方法在低信噪比下有更好的识别率。     

A new approach to analysis of residue probability density function in pipelined ADCs

This paper presents a new approach to analysis of residue probability density function (pdf) in pipelined ADCs. This work was performed based on the fundamental theorem for function of a random variable to map stage input pdf to its output density. It will be shown that residue pdf converges to uniformity. For the stages with half-bit redundancy, this uniformity is accompanied with an extra bit of resolution. Also, the minimum number of stages required to achieve a given value of resolution improvement are studied. Investigating the impact of backend stage on this extra resolution, the appropriate backend to maintain the most extra resolution is proposed. Examining the allowable comparator offsets in different stages, we can see that with decreasing the offset errors in final stages, offset errors impact of the first stages on the final residue pdf and the total converter resolution can be eliminated.     

A method for the measurement of the turn-on condition in MOS transistors

Metal-oxide-silicon (MOS) integrated circuits usually consist of MOS transistors and interconnections. Both, interconnections and MOS transistors are built up of diffused regions in the bulk substrate and conductive strips (metal or polycrystalline silicon) on top of the oxide. For proper electrical operation the interconnection paths should not exhibit MOS transistor effects, i.e. should not induce inversion layers at the silicon-silicon dioxide interface. Furthermore from a designer's point of view it will be desired that some transistors operate in the saturated mode and others in the non-saturated mode. This implies that a method for the determination of the turn-on of channel conduction is highly desirable for designers of MOS integrated circuits. Using a straightforward definition of turn-on, a fast and simple measurement method will be presented for the determination of the relation between gate voltage and diffused region voltage for MOST structures in the turn-on condition.     

Analytical equations for oscillation amplitude of MOS Colpitts oscillator

New analytical equations are presented for amplitude analysis of metal–oxide–semiconductor (MOS) Colpitts oscillator. These equations are obtained from a large signal analysis that includes MOS operation in the saturation, triode and cutoff regions. The analysis is based on a reasonable estimation for the output voltage waveform. The estimated waveform must satisfy the nonlinear differential equations governing the circuit. The validity of the proposed method and the resulting equations has been verified through simulations using TSMC 0.18?µm complementary MOS process. The results are also compared with the other methods. Simulation results show high validity of the proposed equations.     

Internal photoemission in the MOS system at low electric fields in the dielectric. Model and applications

A new model of photoelectric phenomena taking place in the MOS system, at low electric fields in the dielectric layer, is outlined in this article. Solutions of model equations are discussed and compared with the results of experimental investigations. Excellent agreement between the characteristics predicted by the model and the experimental characteristics, strongly supports the validity of the model. Highly precise, new photoelectric measurement methods based on this model are being developed. One of these methods, a method to measure the effective contact potential difference in MOS structures (the φ_MS factor), has already been fully verified and shown to be the most accurate of the existing methods for determination of this parameter. The other method, outlined in this article, is the method of determination of the trapping properties of the MOS structure dielectric, which is currently being optimized and verified experimentally.     

Remarks on Analysis, Design and Amplitude Stability of MOS Colpitts Oscillator

The small-signal analysis shows that the MOS Colpitts oscillator is described by a third order characteristic equation. The procedure for finding the second order approximation is defined, and the solution corresponding to this approximation is found. Then the equations for transistor transconductance describing function are analyzed, and the design procedure corresponding to the "convenient" operation point is given. The same equations are also used for the analysis of amplitude stability in this oscillator. It is shown that the amplitude self-modulation (squegging) in the considered oscillator is absent for any conducting angle of the transistor.     

Computationally efficient equalization for asynchronous cooperative communications with multiple frequency offsets

In cooperative communications, time and frequency synchronization is an important issue needed to be addressed in practice. Due to the nature of cooperative communications, multiple frequency offsets may occur and the traditional frequency offset compensations may not apply. For this problem, equalization for the time-varying channel has been used in the literature, where the equalization matrix inverse needs to be retaken every symbol. In this paper, we propose computationally efficient minimum mean square error (MMSE) and MMSE decision feedback equalizers (MMSE-DFE) when multiple frequency offsets are present, where the equalization matrix inverses do not need to be retaken every symbol. Our proposed equalization methods apply to linear convolutively coded cooperative systems, where linear convolutive space-time coding is used to achieve the full cooperative diversity when there are timing errors from the cooperative users or relay nodes, i.e., asynchronous cooperative communication systems.     

Characteristics of a longitudinal/transverse coupling slot incrossed rectangular waveguides

A rigorous analysis of a broad-wall slot coupler between two crossed rectangular waveguides is presented. The slot is longitudinal and offset from the center line in the main guide and is centered transverse in the branch guide. Integral equations are developed, taking into account finite wall thickness. The integral equations are then solved for the aperture electric field. Coupling slot characteristics are obtained, including the resonant length and dominant mode scattering. Numerical results for resonant length and scattering parameters are presented over a range of offsets, waveguide dimensions, and frequencies     

Carrier frequency offset compensation for uplink of OFDM-FDMAsystems

A frequency offset compensation method for OFDM-FDMA, that can correct offsets after the DFT via circular convolution, is proposed as an alternative to the direct method that corrects frequency offsets by multiplying the complex exponents of the offset estimates before the DFT. In contrast to the direct method whose complexity increases proportional to the number of users, the computational load of the proposed scheme decreases as the number of users increases. It is shown that the proposed method is simpler to implement than the direct method when the number of users is greater than two. Furthermore, the former can outperform the latter, because a frequency offset compensation for one user after the DFT does not affect the data of other users. Computer simulation results demonstrate the advantage of the proposed method     

Decision Feedback Frequency Offset Estimation and Tracking for General ICI Self-Cancellation Based OFDM Systems

Inter-carrier interference (ICI) self-cancellation schemes were often employed in many OFDM systems as a simple and effective approach to suppress ICI caused by carrier frequency errors. The same procedure, however, can not perform very well at high frequency offsets. We propose a simple decision feedback scheme based on the general ICI self-cancellation scheme to perform estimation and tracking of the carrier frequency offsets. A system with the scheme does not consume additional bandwidth since it used the same data symbols employed for ICI cancellation for the estimation. After an initial estimation is completed, the scheme switches to the tracking mode to carry out the estimation of deviations in the frequency offsets. Finally this fine-tuned estimate is applied to the ICI self-cancellation scheme concurrently for frequency offset correction and hence improved the system performance greatly. Simulation results showed that our scheme allowed up to 9% of random variations in the frequency offset. The effectiveness of our scheme is further verified by calculating the bit error rate performance of various OFDM receivers.     

A second-order high-resolution incremental A/D converter withoffset and charge injection compensation

Measurement and instrumentation applications require absolute accuracy, e.g. offset and gain errors cannot be tolerated. These applications are characterized by DC performance such as differential and integral nonlinearities, offset and gain errors, and they often require high resolution. The second-order incremental A/D converter, which makes use of sigma-delta modulation associated with a simple digital filter, is capable of achieving such requirements. Experimental results of circuits fabricated in a SACMOS 3-μm technology indicate that 15-bit absolute accuracy is easily achievable, even with a low reference voltage     

基于Radon-Ambiguity变换的LFM信号时/频差快速联合估计

提出了一种基于Radon-Ambiguity变换(Radon-Ambiguity Transform, RAT)的线性调频(Linear Frequency Modulated, LFM)信号时/频差快速联合估计的算法.根据LFM信号在多个不同角度上的RAT峰值位置建立一组以信号间时差和频差为未知量的方程组,求解方程组即可得到时/频差的估计值.对于存在噪声的信号,RAT误差会导致方程组不能直接求解,为了抑制噪声干扰,采用最小二乘法估计时/频差.本文算法无需计算二维平面上各点的模糊函数值,并且由于离散RAT可以通过快速傅里叶变换快速实现,具有所需运算量低的优点.仿真实验表明,相比于常见的基于模糊函数峰值搜索的时/频差估计算法,本文算法在保证时/频差估计精度的同时能够显著提高运算效率.     

Performance Improvement of DPSK Signal Reception Using Reconfigurable Multiple Bit Differential Detection in the Presence of Carrier Frequency Offset

In this paper we propose a reconfigurable multiple bit differential detection (MBDD) algorithm with diversity reception in the form of postdetection equal-gain combining (EGC) that can be used for the differential phase shift keying (DPSK) signal reception in the presence of significant frequency offsets. The proposed algorithm is based on the MBDD algorithm with the introduction of a mechanism for the estimation of the frequency offset. The algorithm is checking N _c frequency offsets around zero offset and chooses the one that is the most likely. The analysis shows that the receiver with the proposed algorithm provides signal reception with almost equal quality in a wide range of carrier frequency offsets around zero frequency offset.     

Electrical characterization of dielectrically isolated siliconsubstrates containing buried metallic layers

Dielectrically isolated substrates containing buried highly conducting WSi₂ layers are characterized for the first time using MOS capacitors. The active silicon layer is approximately 3 μm thick with a buried WSi₂ layer adjacent to the isolation layer. The buried metal forms the back contact of the capacitor and excellent MOS characteristics are observed. Minority carrier lifetimes in excess of 200 μs were measured indicating the suitability of these substrates for use in device manufacture     

Digital-domain calibration of multistep analog-to-digitalconverters

A digital-domain self-calibration technique, which can directly measure and cancel code errors in multistep conversions, is developed to improve the linearity of multi-step analog-to-digital converters (ADCs). While conventional self-calibration techniques require separate digital-to-analog converters (DACs) for calibration purpose to subtract nonlinearity errors in the analog domain, the proposed digital calibration technique uses add-on digital logic to subtract nonlinearity errors digitally from uncalibrated digital outputs. In a prototype 12-b fully differential two-step ADC implemented using a 2-μm n-well CMOS technology, this technique cancels MOS switch feedthrough, op-amp offsets, and interstage gain errors simultaneously, and improves total harmonic distortion from -64 to -77 dB     

Performance study of n-MOS natural transistor fabricated by low thermal budget process

Natural n-MOS transistor and MOS capacitor test structures have been fabricated by the low temperature process design for better control on device dimensions. Si-SiO₂ interface properties and performance of LPCVD gorwn polysilicon gate natural transistor has been studied through MOS C-V analysis and physical-electrical modeling. Transistor behavior at cryogenic temperatures has also been analysed through MOS C-V characteristics and one dimensional transport equations.     

Compound radiating slots in a broad wall of a rectangular waveguide

An analysis is presented of the characteristics of a broad wall radiating slot, offset from the center line and tilted with respect to the longitudinal axis of a rectangular waveguide. Pertinent integral equations are developed, taking into account finite wall thickness, and are solved for the slot aperture E-field using the method of moments. Compound slot characteristics are then deduced, including resonant length and dominant mode scattering. Numerical results for the scattering from resonant slots are presented over a range of offsets, tilt angles, frequencies and waveguide dimensions. For resonant compound slots, offset and tilt are shown to control the aperture electric-field amplitude with a phase variability of 360°. The results have significant applications in the design of compound slot arrays     

采样时钟偏差对OFDM系统性能的影响

针对采样时钟同步偏差对正交频分复用（Orthogonal Frequency Division Multiplexing，OFDM）系统的影响，建立了数学模型，分别就采样定时偏差和采样频率偏差的影响进行详细分析；经过仿真，从星座图、误码率（Bit—Error—Rate，BER）及信噪比（Signal—to—Noise Ratio，SNR）损失等角度对采样频率偏差的影响做了揭示和验证。结果表明，采样频率偏差会引起信号幅度衰减和子载波间干扰（Inter—Carrier Interference，ICI），导致系统信噪比性能下降；这种影响与子载波位置有关，还会随着OFDM符号数的增多而加剧。     

Minority-carrier lifetime analysis of silicon epitaxy and bulkcrystals with nonuniformly distributed defects

Existing analyses of the pulsed response of an MOS capacitor for minority-carrier lifetime determination result in a lifetime value averaged over most of the depletion region width. The authors present an analysis of MOS capacitance-versus-time data that enables minority-carrier generation lifetime to be plotted as function of depletion-region depth. The technique is shown to be useful for samples with bulk or buried interfacial layer defects that have defect-free surfaces. Data are presented for intrinsically gettered bulk crystals and extrinsically gettered Si (2%Ge) epitaxial layers with misfit dislocations. For samples that do have uniform lifetimes, the measurement time required for determining carrier lifetime is reduced by more than an order of magnitude