用于设计连续时间滤波器的基于混合积分器的双二阶单元

摘要：提出了一种新型基于混合积分器的双二阶单元。与基于源极跟随器的双二阶单元采用正反馈综合复数极点相比,本文提出了另一种综合复数极点的机制。提出的双二阶单元采用负反馈结合不同类型积分器综合复数极点,用于设计连续时滤波器。该单元包括许多优点：电路结构简单、高增益、无寄生极点、不需要共模反馈电路和大的驱动能力。在0.18 μm CMOS 工艺上采用提出的双二阶单元实现了一个4阶巴特沃斯低通滤波器。滤波器包括测试缓冲器有源面积仅为200×170µm。提出的滤波器消耗201µW功耗,获得51dB动态范围。     

Periodic-switching filter networks-a means of amplifying and varying transfer functions

A technique of periodically switching filter networks makes continuously variable filter parameters possible; at the same time capacitor or time-constant multiplication is obtained. With this method the time constants are multiplied by the switching period to switch aperture-time ration. Because the aperture time is usually small compared to the switching period, the active elements can be shared. A typical first-order system is analyzed for its step and sine response by the difference equation method. Phase and gain error expressions are established as a function of the various parameters. Limiting cases are then investigated to give a measure of a pulse- switched system performance. Finally an application of a multiplexed system is presented where three independent transfer functions are realized using one operational amplifier.     

基于加权引导滤波与时域高通滤波的非均匀性校正算法

为解决基于传统时域高通滤波红外图像非均匀性校正算法存在鬼影现象以及固定图案噪声去除不彻底的问题,提出了一种加权引导滤波和改进时域高通滤波相结合的非均匀性校正算法。首先,利用加权引导滤波准确分离红外图像中的空域高频成分;然后,计算红外图像中像素点灰度值变化幅度;最后,在进行时域高通滤波时对红外图像中的运动区域和静止区域使用不同时间常数进行校正。采用两组真实红外图像序列进行实验,并与经典的双边滤波时域高通,均值滤波时域高通非均匀性校正算法进行比较。实验结果表明:文中所提算法在主观视觉和客观评价指标方面优于其他两种算法,有效降低了红外图像的非均匀性,不会产生鬼影,取得了较好的非均匀性校正效果。     

Mixed-integrator-based bi-quad cell for designing a continuous time filter

A new mixed-integrator-based bi-quad cell is proposed. An alternative synthesis mechanism of complex poles is proposed compared with source-follower-based bi-quad cells which is designed applying the positive feedback technique. Using the negative feedback technique to combine different integrators, the proposed bi-quad cell synthesizes complex poles for designing a continuous time filter. It exhibits various advantages including compact topology, high gain, no parasitic pole, no CMFB circuit, and high capability. The fourth-order Butterworth lowpass filter using the proposed cells has been fabricated in 0.18 μm CMOS technology. The active area occupied by the filter with test buffer is only 200×170 μm2. The proposed filter consumes a low power of 201 μW and achieves a 68.5 dB dynamic range.     

New technique for designing nearly orthogonal wavelet filter bankswith linear phase

A new technique based on nonlinear optimisation to design nearly orthogonal wavelet filter banks with linear phase is proposed. The main idea is to impose a certain number of zeros at z=-1 for a symmetric filter and make it satisfy the power complementary condition as accurately as possible. From this filter, a semi-orthogonal wavelet filter bank which is nearly orthogonal can be constructed. This semi-orthogonal filter bank can be approximately implemented using a filter bank consisting of only one prototype filter. The frequency selectivity can also be designed at the same time by using a weighted cost function     

Time domain approach to recursive digital filter synthesis

The problem of the design of IIR digital filters, when the analog filter has been synthesized, resides in the approximation of a continuous system by means of a discrete one. We present a synthesis method which discretizes an Input-State-Output (I-S-O) model of the analog filter and is completely performed in the time domain. The basis of the method is the way in which the problem is stated, which points out the fundamental role played by the interpolator and allows an easy implementation.The main advantages of our method, with reference to traditional approaches, are:

• •- it allows direct working on continuous representations of the analog filter and the discretization does not require symbolic calculations as in approaches based on substitution techniques (for example bilinear transformation);
• •- it is completely numerical and is very simple from a computational point of view;
• •- it can be used for single and multiple input-output filters;
• •- it allows longer sampling periods using suitable interpolators.

An example is discussed which allows a comparison with the synthesis method based on bilinear transform and shows, also, that computing time may be saved as the sampling period may be traded off with the interpolator order.     

Adaptive filter for microwave radiometry

An adaptive filter, which combines the advantages of both short (about 0.5 s) and long (about 2 min) integrating time constants, is described. The recording time constant will be long for a steady level of input signal, but will proportionally shorten when there is a change in the average level of the input signal. If steady conditions continue after a change, the time constant will gradually become long again.     

Efficient tunable IIR and allpass filter structures

A new recursive filter structure is proposed which can be controlled on-line using a single parameter. The structure can be used for interpolation in timing synchronisation of digital communications receivers. The technique is illustrated with an example of the implementation of a tunable fractional delay allpass filter using the Thiran design technique     

Band-pass correlation filter for illumination- and noise-tolerant face recognition

The paper proposes a band-pass correlation filter in frequency domain for frontal face recognition task under both poor illumination and noisy condition. The band-pass nature of the proposed filter is achieved through combination of a modified high-pass filter and a continuous wavelet filter. An optimal range of scale is selected for this wavelet filter. The performance of the proposed band-pass correlation filter for face recognition tasks under variations in illumination and noise is evaluated and compared with other filters using standard databases (YaleB and PIE). High recognition accuracy is achieved in this proposed technique.     

Variable digital filter design using the outer product expansion

Digital filters with adjustable frequency domain characteristics are referred to as variable digital filters. Variable filters are useful in the applications where the filter characteristics are required to be changeable during the course of signal processing. Especially in real time applications, variable filters are needed to change their coefficients instantaneously such that the real time signal processing can be performed. The present paper proposes a very efficient technique for variable 1D digital filter design. Generally speaking, the variable coefficients of variable digital filters are multidimensional functions of a set of spectral parameters which define the desired frequency domain characteristics. The authors first sample the given variable 1D magnitude specification and use the samples to construct a multidimensional array, then propose an outer product expansion method for expanding the multidimensional array as the sum of outer products of 1D arrays (vectors). Based on the outer product expansion, one can reduce the difficult problem of designing a variable 1D digital filter to the easy one that only needs constant 1D filter designs and 1D polynomial approximations. The technique can obtain variable 1D filters having arbitrary desired magnitude characteristics with a high design accuracy     

Shunt active filter for reactive power compensation

A simple control technique for three-phase shunt active filters without computation of the reactive current component is presented. A current controller with fast dynamics for an active filter is described. Reactive current is directly controlled without the need for sensing and computing the reactive component of the load current, thus simplifying the control system. Current compensation is done in the time domain, allowing a fast time response. The dc voltage control loop keeps the voltage across the dc capacitor constant. High power factor control by an active filter is described. All control functions are implemented in software using a singlechip microcontroller, thus simplifying the control circuit. Any current-controlled synchronous rectifier can be used as a shunt active filter through only the simple modification of the software and the addition of current sensors. It is shown through experimental results that the proposed controller gives good performance for the shunt active filter.     

A novel track maintenance algorithm for PHD/CPHD filter

Probability hypothesis density (PHD) filter and cardinalized PHD (CPHD) filter have proved to be promising algorithms for tracking an unknown number of targets in real time. However, they do not provide the identities of the individual estimated targets, so the target tracks cannot be obtained. To solve this problem, we propose a new track maintenance algorithm based on the cross entropy (CE) technique. Firstly, the particle filter PHD (PF-PHD) algorithm is used to estimate the target states and the target number. Then, the results of the estimation are used as vertexes to construct a connectivity graph with associated weights, and the CE technique is employed as a global optimization scheme to calculate the optimal feasible associated events. Furthermore, due to the advantages of the CPHD filter and the Rao-Blackwellized particle filter (RBPF), we propose another track maintenance algorithm based on the CE technique, named the RBPF–CPHD tracker, which can further improve the track maintenance performance due to the more accurate state estimates and their number estimates. Simulation results show that the proposed algorithms can effectively achieve the track continuity, with stronger robustness and greater anti-jamming capability.     

滤光片分光型高光谱相机发展现状及趋势（特邀）

高光谱相机可将成像技术与光谱探测技术相结合,在对目标空间特征成像的同时,可以对每个空间像元形成多个窄波段实现连续的光谱覆盖,不同光谱信息能充分反映地物内部的物理结构、化学成分的差异。与传统的空间二维成像相比,高光谱相机可以同时获取目标的空间和光谱信息,在一定的空间分辨率下,能够获取宽谱段范围内地物独有的连续特征光谱,对地物的精准识别和探测具有显著优势,目前已成为对地遥感重要的前沿技术手段,在农、林、水、土、矿等资源调查与环境监测等领域具有重要的应用价值。随着滤光片镀膜技术的飞速发展,极大地促进了滤光片分光型高光谱相机的研制,目前基于滤光片分光原理的高光谱相机以大幅宽、高空间分辨率、高光谱分辨率和轻小型的优势成为高光谱遥感载荷的重要组成部分,在微纳卫星高光谱星座组网中获得广泛应用。主要对滤光片分光型的高光谱相机进行了综述,介绍了国内外典型滤光片分光型星载高光谱成像载荷,以及地面在研的滤光片分光型高光谱成像系统,并分析了这些系统的技术方案、性能指标及应用前景,阐述了基于滤光片分光原理的高光谱相机的技术特点和优缺点,最后展望了滤光片分光型高光谱相机的发展趋势。     

Tunable photonic bandpass filter with high-frequency response performance

A continuously tunable RF/microwave photonic bandpass filter that simultaneously achieves high skirt selectivity and high stopband attenuation is presented. It is based on controlling the signal polarisation state in a reflective amplified recirculating delay line loop with a polariser at the output. A technique to overcome the phase noise limitation in the structure is also presented. Experimental results demonstrate continuous tuning of the high-performance photonic bandpass filter and a continuously tunable photonic bandpass filter with a low-noise performance.     

Digital filter bank design quadratic-constrained formulation

Formulate the filter bank design problem as an quadratic-constrained least-squares minimization problem. The solution of the minimization problem converges very quickly since the cost function as well as the constraints are quadratic functions with respect to the unknown parameters. The formulations of the perfect-reconstruction cosine-modulated filter bank, of the near-perfect-reconstruction pseudo-QMF bank, and of the two-channel biorthogonal linear-phase filter bank are derived using the proposed approach. Compared with other design methods, the proposed technique yields PR filter banks with much higher stopband attenuation. The proposed technique can also be extended to design multidimensional filter banks     

Two-electrode DFB laser filter used as a wide tunable narrow-bandFM receiver: tuning analysis, characteristics and experimental FSK-WDMsystem

Characteristics of a two-electrode DFB laser filter are studied both theoretically and experimentally. Using a matrix analysis of spontaneous emission, a continuous tuning range of 6.7 Å is achieved by changing both net field gains of the two electrodes. A total discontinuous tuning range of over 10 nm comprising alternating mode jumps and continuous tuning range of 4 Å are measured experimentally. The laser filter presents a FWHM bandwidth of 5 GHz which depends on the optical input power. In addition, it is demonstrated that a DFB laser filter can act as a frequency discriminator/photodetector, i.e., a narrow-band FM receiver, with a uniform bandwidth of 1.5 GHz. Using the two-electrode DFB laser for both transmitter and receiver, a two-channel FSK-WDM transmission system utilizing the discontinuous tuning range is reported. The advantage of such a device is the simplicity as compared to the heterodyne technique     

Generalized digital Butterworth filter design

This correspondence introduces a new class of infinite impulse response (IIR) digital filters that unifies the classical digital Butterworth filter and the well-known maximally flat FIR filter. New closed-form expressions are provided, and a straightforward design technique is described. The new IIR digital filters have more zeros than poles (away from the origin), and their (monotonic) square magnitude frequency responses are maximally flat at ω=0 and at ω=π. Another result of the correspondence is that for a specified cutoff frequency and a specified number of zeros, there is only one valid way in which to split the zeros between z=-1 and the passband. This technique also permits continuous variation of the cutoff frequency. IIR filters having more zeros than poles are of interest because often, to obtain a good tradeoff between performance and implementation complexity, just a few poles are best     

Analog active filter component selection with nature inspired metaheuristics

The most crucial design step for analog active filter design is the optimal selection of passive component values due to manufactured constants. Since the search on possible combinations in preferred values for capacitors and resistors is an exhaustive process, it has to be automated with high accuracy within short computation time. In this work, two nature inspired metaheuristics, differential evolution (DE) and harmony search (HS) algorithms are utilized for optimal filter design considering different topologies and manufacturing series. Simulation results show that as global optimization methods both DE and HS minimize the total design error and reduce the elapsed time with respect to previously utilized methods.     

X波段腔体带通滤波器的设计与实现

通过耦合系数法设计滤波器,并通过HFSS进行精确仿真,采用时域调试法完成调试,大大缩短了研制周期,实现了X波段内三个不同中心频率的腔体带通滤波器,具有相对较高的中心频率且腔数多达10。经测试表明,所有滤波器均具有较低的通带插入损耗和较高的带外抑制。