Design of multilevel decision feedback equalizers

Multilevel decision feedback equalization scheme (MDFE) is an efficient and simple realization of the fixed-delay tree search with decision feedback (FDTS/DF) for channels using RLL(1,k) codes. In MDFE, the entire tree-search is replaced with a 2-tap transversal filter and a binary comparator with negligible loss in performance. This 2-tap filter can be combined with the forward and feedback equalizers resulting in a structure that is physically identical to DFE but requires very different equalizer settings. This paper focuses on equalizer design for MDFE. It is first shown that the MDFE scheme can also be derived without using the principle of tree-search by exploiting the run-length constraints imposed by the RLL(1,k) code in conjunction with the maximization of an appropriately defined signal-to-noise ratio (SNR). Recognizing that a multilevel eye Is formed at the comparator, we define this SNR as the eye-opening divided by noise plus intersymbol interference. This formulation directly leads to a novel adaptive scheme based on the well known LMS algorithm. The relationship between this work and the earlier derivation of MDFE is then clarified. We also develop a noniterative analytical approach for the optimum equalizer design. Because of the economy of implementation, there is particular interest in the design of continuous-time forward equalizers. A noniterative analytic design approach, which does not suffer from local minima problems, is developed for such equalizers. Computer simulation results are presented for comparing the different design approaches     

Dual FDTS/DF: a unified approach to dual-detection and modificationfor MTR codes

Dual-detector decision-feedback schemes have recently gained considerable interest in magnetic recording. Schemes such as dual decision feedback equalization (DDFE), M2DFE, and dual FDTS/DF are dual-detector versions of DFE, multilevel DFE (MDFE), and fixed delay tree search with decision feedback fixed-delay tree search with decision feedback (FDTS/DF) detectors, respectively. At high recording densities, the dual-detector versions significantly improve bit-error-rate (BER) performance and reduce error propagation. In this paper, we first give a unified approach to the bit-error-rate analysis of dual-detector decision feedback schemes in an attempt to highlight their relationship, and then we show that the performance of dual FDTS/DF reduces to that of DDFE for τ=0 and reduces to that of M2DFE for τ=1 with d=1 code constraint. Further, we extend the dual FDTS/DF detection scheme to maximum transition run-length (MTR) coded channels. On the basis of both BER and error event analysis, we propose a modified dual FDTS/DF detection scheme for MTR-coded channels that improves BER performance. The new scheme modifies certain bits in the detection profess for preventing the dominant error event. Simulation results on 6/7 MTR-coded Lorentzian channel show that the modified detector gives around 1 dB SNR improvement over the advanced (trellis-coded extended partial response) TC-E²PR detector     

Performance analysis of a monolithic integrated transversal filter using mixed-mode scattering parameters

A broadband transversal filter based on a new cell design that enables positive and negative tap gain weight control is proposed and its behaviour is analysed in the frequency domain. The non-ideal behaviour of distributed circuits and associated effects on the functional characteristics of an integrated transversal filter design are examined through consideration of the principles of generic differential circuits. It is shown that the transversal filter can be modelled as a coupled-pair drain line structure with the ability to propagate both common and differential-mode signals. Coupled wave interactions on artificial transmission lines are characterised using a set of derived mixed-mode scattering parameters and voltage and current phasors at input/output ports of a monolithic filter design. Analytical and simulation results confirm the suitability of the approach for broadband filter implementations, in applications requiring predefined time-domain responses as in high-speed correlators and encoders as used in optical code division multiple access (CDMA) systems.     

Absolute strain measurements made with fiber bragg grating sensors

A strain sensor system based on optical fiber Bragg gratings (FBGs) is proposed with a new matched-filter design. The strain variation on the sensor FBG is continuously followed and matched by a filter FBG by use of a feedback control loop that produces an identical strain condition on the filter FBG. The matched strain on the filter FBG is then determined from the resonance vibration of the fiber piece embedding the filter FBG. The implementation and the performance of the proposed system are described. It is demonstrated that the proposed system can distinguish strain variation on the sensor FBG with resolution of one microstrain.     

Durable diamond-like carbon templates for UV nanoimprint lithography

The interaction between resist and template during the separation process after nanoimprint lithography (NIL) can cause the formation of defects and damage to the templates and resist patterns. To alleviate these problems, fluorinated self-assembled monolayers (F-SAMs, i.e.?tridecafluoro-1,1,2,2,tetrahydrooctyl trichlorosilane or FDTS) have been employed as template release coatings. However, we find that the FDTS coating undergoes irreversible degradation after only 10 cycles of UV nanoimprint processes with SU-8 resist. The degradation includes a 28% reduction in surface F atoms and significant increases in the surface roughness. In this paper, diamond-like carbon (DLC) films were investigated as an alternative material not only for coating but also for direct fabrication of nanoimprint templates. DLC films deposited on quartz templates in a plasma enhanced chemical vapor deposition system are shown to have better chemical and physical stability than FDTS. After the same 10 cycles of UV nanoimprints, the surface composition as well as the roughness of DLC films were found to be unchanged. The adhesion energy between the DLC surface and SU-8 is found to be smaller than that of FDTS despite the slightly higher total surface energy of DLC. DLC templates with 40?nm features were fabricated using e-beam lithography followed by Cr lift-off and reactive ion etching. UV nanoimprinting using the directly patterned DLC templates in SU-8 resist demonstrates good pattern transfer fidelity and easy template-resist separation. These results indicate that DLC is a promising material for fabricating durable templates for UV nanoimprint lithography.     

基于误差的观测器在光电跟踪系统中的应用

对于光电跟踪系统来说,图像传感器例如电荷耦合器件(CCD)只能够探测脱靶量即偏差信息,而无法得到目标运动轨迹,所以,大多数情况下在目标跟踪回路不能直接实现前馈控制,这限制了系统的闭环跟踪性能。本文采用了一种基于误差观测器的等效前馈控制方法来提高运动平台光电跟踪系统的跟踪性能。该方法是在原有的反馈控制回路的基础上加入一个观测前馈通路,通过优化前馈滤波器提高闭环性能。由于是基于最终的视觉误差的观测,该方法对目标跟踪和扰动抑制同时起作用,既可以应用到地基跟踪也可以应用于运动平台上。前馈滤波器没有采用简单的一阶低通滤波器而是选择Q₃₁滤波器。仿真和实验表明,与传统控制方法相比,这种基于误差观测器的控制方法能够有效提高系统的低频跟踪性能。

     

Non‐linear feedback control of the p 53 protein–mdm 2 inhibitor system using the derivative‐free non‐linear Kalman filter

It is proven that the model of the p 53–mdm 2 protein synthesis loop is a differentially flat one and using a diffeomorphism (change of state variables) that is proposed by differential flatness theory it is shown that the protein synthesis model can be transformed into the canonical (Brunovsky) form. This enables the design of a feedback control law that maintains the concentration of the p 53 protein at the desirable levels. To estimate the non‐measurable elements of the state vector describing the p 53–mdm 2 system dynamics, the derivative‐free non‐linear Kalman filter is used. Moreover, to compensate for modelling uncertainties and external disturbances that affect the p 53–mdm 2 system, the derivative‐free non‐linear Kalman filter is re‐designed as a disturbance observer. The derivative‐free non‐linear Kalman filter consists of the Kalman filter recursion applied on the linearised equivalent of the protein synthesis model together with an inverse transformation based on differential flatness theory that enables to retrieve estimates for the state variables of the initial non‐linear model. The proposed non‐linear feedback control and perturbations compensation method for the p 53–mdm 2 system can result in more efficient chemotherapy schemes where the infusion of medication will be better administered.Inspec keywords: proteins, molecular biophysics, biochemistry, Kalman filters, inverse problems, perturbation theoryOther keywords: nonlinear feedback control, p53 protein‐mdm2 inhibitor system, derivative‐free nonlinear Kalman filter, differential flatness theory, protein synthesis loop, diffeomorphism, protein synthesis model, feedback control law, nonmeasurable elements, modelling uncertainties, inverse transformation, nonlinear model, perturbation compensation method, chemotherapy schemes, medication infusion     

Transversal recording on radially anisotropic disc

Transversal recording has been described in the sixties, as a promising mode to achieve high density magnetic recording [1]. Because of the improvements in longitudinal and vertical recording introduced by thin film technologies for heads and media, research labs took no further interest in this transversal mode, partly due also to the fact that media and heads were not available at that time. However technological advances of recent years such as the attainment of high B(H) loop squareness for amorphous or crystallized magnetic alloys such as CoxSm1-x[2] and the capability of conventional ferrite heads to record vertical bits on a strongly anisotropic medium [3] allow us to assert that transversal magnetic recording (TMR) can be developed today. This paper describes recent studies for a radially anisotropic disc on a new TMR system. Experimental results on Co-Sm are presented, and the complementary features between the transversal mode and both vertical and longitudinal magnetic recording are discussed.     

适用于QAM信号的方形判决超指数迭代盲均衡算法

针对超指数迭代判决反馈(Super-Exponential Iteration Decision Feedback Equalization,SEI-DFE)盲均衡算法在水声通信系统中表现出的收敛性差的问题,提出了一种基于正方形判决的修正超指数迭代判决反馈盲均衡算法。该算法在修正超指数算法的基础上,引入判决正方形机制分别对输出信号的同相分量和正交分量进行均衡,以进一步提高相位补偿能力;在判决反馈均衡器中引入二阶数字锁相环,实现对相位旋转的跟踪和补偿。消声水池实验采用16QAM调制信号,从滤波器阶数、步长以及Q矩阵大小三个方面对算法的影响来验证算法的误码率性能,结果表明,新算法的误码率相比修正超指数迭代判决反馈(Modified Super-Exponential Iteration Decision Feedback Equalization,MSEI-DFE)算法改善了两个量级,实现了对相位旋转的有效补偿,大大改善了载波恢复性能。     

Digital feedback loops for d.c. SQUIDs

Digital feedback loops for d.c. SQUIDs using pulse-rate modulation are proposed and investigated by simulations and measurements. The design of a d.c. SQUID magnetometer yields a simulated energy resolution of ≈ 11 h (h = Planck's constant) where ≈ 3 h corresponds to additional noise due to the feedback loop. Measurements at Josephson sampler prototype chips showed that the digital feedback loop is very stable and fast enough to obtain a flicker-free display on an oscilloscope. In contrast to conventional feedback loops an integration of sensor and feedback loop on one or several chips with Josephson junctions seems feasible.     

Optoelectronic approach to adaptive radio-frequency transversal filter implementation with negative coefficients by using optical spectrum shaping

A multitap negative and positive coefficient radio-frequency transversal filter is implemented by using a digital-micromirror-device spatial light modulator for weighting-factor control and a chirped fiber Bragg grating for time-delay control. The demonstrated architecture is reconfigurable, has high speed and low loss, and is robust through digital programmability for a wide variety of filtering algorithms. A design using an interleaver for differential detection realizes an ultrahigh bandwidth with a maximum processable frequency of 33.7 GHz. A multitap low-pass filter, a negative tap notch filter with 40 dB attenuation, and a multitap negative coefficient bandpass filter are experimentally demonstrated. The results are in agreement with theory.     

Design of withdrawal-weighted SAW filters

Presents a new design algorithm for a withdrawal-weighted surface acoustic wave (SAW) transversal filter. The proposed algorithm is based on the effective transmission loss theory and a delta function model of a SAW transversal filter. The design process consists of three steps, which eventually determine eight geometrical design parameters for the filter in order to satisfy given performance specifications. First, the number of fingers in the input and output interdigital transducers (IDTs), plus their geometrical sizes is determined using the insertion loss specification. Second, the number and positions of the polarity reverses in the output IDT are determined using the bandwidth and ripple specifications. Third, the number and position for withdrawing and switching specific fingers in the output IDT and attached electrode area are determined to achieve the desired sidelobe level. The efficiency of the technique is illustrated using a sample design of an IF filter consisting of a uniform input IDT and withdrawal-weighted output IDT     

负载加速度反馈的伺服系统谐振抑制

谐振常常造成伺服系统不稳定,影响其控制性能.首先建立光电控制系统的动力学方程,分析了谐振和反谐振产生的原因.伺服系统同样也受到反谐振的影响,并且反谐振出现在谐振之前.由于间隙和摩擦的影响,谐振往往会随之变化,很难用固定的陷波器去补偿.提出一种负载加速度反馈控制算法减小谐振的影响,由此形成三闭环控制模式.根据提出的加速度反馈算法3条准则设计加速度控制器,采用此控制方法速度闭环带宽提高了5Hz左右,谐振峰减小了15dB.并且200Hz以后的谐振迅速衰减,提高了系统的稳定性.     

Infinite impulse response microwave photonic filter using a dual drive modulator with an optoelectronic feedback loop

A novel design of a microwave photonic filter with infinite impulse response is demonstrated. The design is based on a dual drive modulator with an optoelectronic feedback loop. The stopband of the filter can be switched to passband and vice versa by switching the bias point of the dual drive modulator. Measured results confirm the theoretical expressions and demonstrate a rejection ratio and frequency selectivity which is greater than 30 dB.     

Evaluation of the design requirements for the electrical part oftransmission-type optical smoke detector to improve its thresholdstability to slowly varying influences

The output signal sensitivity to optical component contamination and other slowly varying parasitic influences in the transmission-type smoke detector is analyzed. The analysis carried out the new topology characterized by the selective feedback loop incorporating the optical part of the detector. Depending on the loop gain frequency shaping in the electrical part of the loop, dual-stability enhancement of the input threshold level can be achieved. The stable dc output signal can be preserved by the high dc loop gain value, as an option to the standard serial filter dc rejection. The detector passband gain stability is achieved by the high loop gain selectivity, eliminating feedback at very low or passband frequencies. The proposed topology can be easily adopted to both digital and low-cost analog detector designs. The special case of the threshold sensitivity neutralization through the cancellation of the output dc signal sensitivity and passband gain sensitivity is considered, too, as an option suitable for low-cost detectors. In addition to the described linear settlement, two nonlinear solutions are presented, the first of them based on the foregoing linear circuit analysis. Despite its nonlinear nature, this alternative solution is not troublesome for analog implementation, since the nonlinear function required is realized by the standard variable gain amplifier. Another nonlinear method requires logarithmic function implementation, so that its suitability depends on the particular design requirements     

不确定系统的多指标约束滤波器设计

研究了一类不确定系统的滤波器多指标设计问题．以线性矩阵不等式为工具设计了状态反馈律，使系统的闭环满足稳态协方差约束，同时使系统的闭环极点落在指定的圆盘内．最后，用一个数值算例验证了设计方法的可行性．     

Selection of the common-mode feedback network connection of fully differential Gm-C filters

It is well known that fully differential (FD) structures have many advantages over their single-ended counterparts. However, the main disadvantage of FD circuit is the potential instability caused by the inherent common-mode (CM) positive feedback loop. To solve such an instability problem, extra common-mode feedback (CMFB) and/or common-mode feedforward (CMFF) circuitries are often incorporated to stabilise the circuits. We present a systematic method for checking the stability condition and identifying the most suitable CMFB network connection for a particular FD Gm-C filter. It has been demonstrated that the CMFB network connection that provides highest CM rejection is not necessarily the conventional arrangement commonly used in FD Gm-C design.     

Fully reconfigurable photonic microwave transversal filter based on digital micromirror device and continuous-wave, incoherent supercontinuum source

The combined use of a programmable, digital micromirror device (DMD) and an ultrabroadband, cw, incoherent supercontinuum (SC) source is experimentally demonstrated to fully explore various aspects on the reconfiguration of a microwave filter transfer function by creating a range of multiwavelength optical filter shapes. Owing to both the unique characteristic of the DMD that an arbitrary optical filter shape can be readily produced and the ultrabroad bandwidth of the cw SC source that is 3 times larger than that of Er-amplified spontaneous emission, a multiwavelength optical beam pattern can be generated with a large number of wavelength filter taps apodized by an arbitrary amplitude window. Therefore various types of high-quality microwave filter can be readily achieved through the spectrum slicing-based photonic microwave transversal filter scheme. The experimental demonstration is performed in three aspects: the tuning of a filter resonance bandwidth at a fixed resonance frequency, filter resonance frequency tuning at a fixed resonance frequency, and flexible microwave filter shape reconstruction.     

Noise and dynamic range optimization of SAW transversal filters

A model for surface acoustic wave (SAW) transversal filters with special attention to the system and circuit designer's point of view is summarized. In the ideal situation the SAW transversal filter is driven with a voltage and the short-circuit current is sensed, which results in a minimization of the triple transit echo distortion. The aperture (width) of the SAW device is the only parameter that is not determined by the frequency dependence of the transfer and therefore it can be used to optimize the SAW device in relation to the electronic circuitry. Noise and dynamic range calculations on an amplifier-filter-amplifier configuration, are performed. It is shown that for a low noise floor at the input of the SAW device, the aperture of this device should be chosen large. However, the dynamic range of the amplifier-filter-amplifier configuration can be maximized by choosing a small aperture.     

Phase-shift fiber-loop ring-down spectroscopy

Fiber-loop ring-down spectroscopy (FLRDS) is a recently developed absorption spectroscopic technique suitable for very small liquid samples. It is based on measurements of the optical decay constant of laser intensity in a loop made of optical waveguide material. This decay constant changes as small liquid samples containing absorbing species are introduced into the loop. In this report, it is demonstrated that one can also obtain the optical decay constant using a continuous wave laser beam that is intensity modulated and then coupled into an optical fiber loop. The inherent exponential decay in the fiber loop introduces a phase shift of the light emitted from the loop with respect to the pumping beam. By measuring this phase shift, one can readily determine the concentration of the analyte introduced between the two fiber ends and a model is established to describe the relationship. It is demonstrated that this technique, dubbed phase-shift fiber-loop ring-down spectroscopy (PS-FLRDS), is well suited as an absorption detector for any flow system in which the optical absorption path is limited by the instrument architecture. By measuring the phase angle as a function of concentration of 1,1'-diethyl-4,4'-dicarbocyanine iodide in dimethyl sulfoxide, the detection limit was determined as approximately 6 microM for a 30-40-microm absorption path. A temporal resolution of approximately 100 ms was demonstrated by a rapid displacement of the solutions between the two fiber ends. Proof-of-principle use of the PS-FLRDS detection in capillary flow systems using a commercial four-way microcross established that the alignment of the fiber and the capillary can be made simple and effective, while retaining both a low detection limit and a fast response.