Antialiasing inputs for charge-coupled devices

An input scheme for analog charge-coupled signal-processing devices has been developed that acts as a prefilter to suppress the aliasing frequencies produced by the sampled-data nature of the CCD. Each charge packet injected into the CCD is a sum of several weighted subsamples taken at a multiple of the CCD clock rate. Various approaches that differ in their rates of oversampling and in their time periods over which subsamples are combined have been compared with respect to their usefulness to produce a sharp cutoff prefilter. A particular implementation using only a factor of 2 oversampling but an averaging period that extends over two CCD clock periods results in a good prefilter characteristic and has been applied to a charge-coupled split-electrode transversal filter. Different implementations of the basic scheme and layout considerations are discussed.     

Multiwavelet prefilters. II. Optimal orthogonal prefilters

For pt.I see IEEE Trans. Circuits Syst. II, vol.45, p.1106-12 (1998). Prefiltering a given discrete signal has been shown to be an essential and necessary step in applications using unbalanced multiwavelets. In this paper, we develop two methods to obtain optimal second-order approximation preserving prefilters for a given orthogonal multiwavelet basis. These procedures use the prefilter construction introduced in Hardin and Roach (1998). The first prefilter optimization scheme exploits the Taylor series expansion of the prefilter combined with the multiwavelet. The second one is achieved by minimizing the energy compaction ratio (ECR) of the wavelet coefficients for an experimentally determined average input spectrum. We use both methods to find prefilters for the cases of the DGHM and Chui-Lian (CL) multiwavelets. We then compare experimental results using these filters in an image compression scheme. Additionally, using the DGHM multiwavelet with the optimal prefilters from the first scheme, we find that quadratic input signals are annihilated by the high-pass portion of the filter bank at the first level of decomposition.     

Integrated switched-capacitor low-pass filter with combined anti-aliasing decimation filter for low frequencies

A new combined antialiasing decimation filter is presented which allows the implementation of a low-frequency switched-capacitor filter on a single chip. Experimental results are presented for a CMOS second-order low-pass filter with 1 dB passband ripple, a cutoff frequency of 2 Hz, and a dynamic range of 84 dB. The decimation filter converts the input clock of 16 kHz into an output clock of 250 Hz. The integrated anti-aliasing filter has a low pole frequency of about 3 kHz.     

Optimization of symbol timing recovery for QAM data demodulators

This paper describes an effective technique for the optimization of the clock recovery circuit in an all-digital modem for linearly modulated signals. Starting from the concept of prefiltering of the data signal (already pursued by these authors in the context of analog data receivers), it is shown how to design an optimum digital prefilter for the minimization of jitter due to both Gaussian and pattern noise in the closed-loop clock recovery scheme by Gardner (1986). The numerical results of the theoretical analysis, obtained after iterative resolution of a constrained-minimum problem via the Lagrange multiplier method, are checked by simulation and can be nicely justified by the consideration of the frequency response of the optimum prefilter. The key outcome of such an approach is the demonstration of a substantial performance improvement in terms of steady-state clock jitter, even with remarkably simple FIR prefilters with a small number of taps     

KALP: a Kalman filter-based adaptive clock method with low-passprefiltering for packet networks use

We consider the issue of source clock frequency recovery in packet networks and propose a new adaptive clock method based on the Kalman filter (KF) with low-pass prefiltering-KALP (Kalman filter-based Adaptive clock method with Low-pass Prefiltering) in short. Noting that because of the difficulty in modeling as well as the nonwhite Gaussian nature of the packet jitter most existing adaptive clock methods could not successfully adopt the Kalman filter, we take a new approach to packet jitter modeling for the KALP. We model the packet jitter not directly but after shaping its characteristics by low-pass prefiltering. This low-pass prefiltering is an important arrangement as it helps to convert the packet jitter into a low-pass signal regardless of its original characteristics, thus enabling to model the prefiltered packet jitter using a simple first-order autoregressive [AR(1)] process. The low-pass prefilter should be carefully selected not to lose the timing information while prefiltering, and the moving averager employed in this paper satisfies this requirement. The AR(1)-modeled jitter component is amenable to the KF-based processing, which in this case becomes an optimal estimator. The design parameters including the initial conditions of the KF and AR(1) parameters can be determined based on the service clock specification and packet interarrival times during the delay smoothing process. We carry out various simulations to compare the performance of the KALP with the existing buffer-based adaptive clock method and demonstrate that the KALP can significantly reduce the fluctuation in the level of receiving buffer as well as the time to recover the source clock frequency     

Filters with active tuning for power applications

Filters for switched-mode power converters have traditionally relied on low-pass networks-with corner frequencies well below the ripple fundamental-to attenuate switching harmonics over a range of frequencies. The filters explored in this report provide extra attenuation at discrete frequencies, easing the filtering requirement of accompanying low-pass networks. When a converter's switching frequency is tuned to a filter resonance using a novel phase-lock control scheme, a resonant filter can match the ripple-attenuation performance of a low-pass network for less volume, weight, and expense. The design and application of resonant filters and active-tuning control are discussed, and experimental results from the input filter and power stage of a prototype DC-DC converter are presented.     

Generalized Discrete Multiwavelet Transform With Embedded Orthogonal Symmetric Prefilter Bank

Prefilters are generally applied to the discrete multiwavelet transform (DMWT) for processing scalar signals. To fully utilize the benefit offered by DMWT, it is important to have the prefilter designed appropriately so as to preserve the important properties of multiwavelets. To this end, we have recently shown that it is possible to have the prefilter designed to be maximally decimated, yet preserve the linear phase and orthogonal properties as well as the approximation power of multiwavelets. However, such design requires the point of symmetry of each channel of the prefilter to match with the scaling functions of the target multiwavelet system. It can be very difficult to find a compatible filter bank structure; and in some cases, such filter structure simply does not exist, e.g., for multiwavelets of multiplicity 2. In this paper, we suggest a new DMWT structure in which the prefilter is combined with the first stage of DMWT. The advantage of the new structure is twofold. First, since the prefiltering stage is embedded into DMWT, the computational complexity can be greatly reduced. Experimental results show that an over 20% saving in arithmetic operations can be achieved comparing with the traditional DMWT realizations. Second, the new structure provides additional design freedom that allows the resulting prefilters to be maximally decimated, orthogonal and symmetric even for multiwavelets of low multiplicity. We evaluated the new DMWT structure in terms of computational complexity, energy compaction ratio as well as the compression performance when applying to a VQ based image coding system. Satisfactory results are obtained in all cases comparing with the traditional approaches.     

New compact low-pass filter (LPF) using cascaded square open loop resonator

This article introduces a new design technique of low-pass filter using cascaded square open loop resonator (SOLR) for the multi-wireless communication system. In the design procedure, a half-wavelength SOLR is realized with 6 GHz to meet the desired LPF cut off frequency. As the resonator is fed by a direct connection of 50-ohm input/output ports, the structure is directly transferred into a second-order low-pass filter with elliptic behavior. An equivalent circuit is extracted and its lumped elements are computed to support the proposed second-order LPF. Based on the equivalent circuit, highly selective third and fifth-order LPFs with wide rejection band are developed. To achieve this development several SOLR are cascaded by a direct connection. The designed filters are implemented on a grounded substrate which has relative permittivity of 6.15 and thickness of 0.508 mm. To verify the design concept, a third-order LPF using two cascaded SOLRs is designed, simulated, fabricated and measured. The filter responses obtained from theory, simulation, and measurement show good agreement. The filter has very small circuit area about 31 mm² excluding the input/output feeding ports.     

一种新型的跟踪低通滤波器

介绍了一种新型的跟踪低通滤波器的原理及实现方法.该跟踪低通滤波器用八阶椭圆型开关电容滤波器MAX293构成低通滤波电路,输入信号的频率通过单片机的测量、修正、倍频处理后输出作为MAX293的时钟控制频率,用以控制MAX293的截止频率从而实现跟踪滤波.实验证明,对于0.1 Hz～25 kHz的信号,跟踪低通滤波器的截止频率相对误差小于1%.     

基于AOA的多功能二阶电流模式滤波器及仿真

以AOA电流模式多路输出积分器和AOA电流模多路输出比例电路为基础,设计了多功能二阶电流模式滤波器。该电路既可通过改变输入信号的作用点,从同一端口分别实现高通、带通和低通滤波,又可从同一端口输入信号,从不同端口同时实现高通、带通和低通滤波,真正实现了多功能滤波。计算机仿真证明该滤波器正确有效。     

Delayless method to generate current reference for active filters

Active power filters are used to eliminate AC harmonic currents by injecting equal but opposite compensating currents. Successful control of active filters requires, among other things, an accurate current reference. In this paper, we introduce a multistage adaptive filtering system which generates the current reference delaylessly and accurately. Our filter structure combines a low-pass prefilter and an adaptive predictive filter, making it possible to extract the sinusoidal active current from the distorted waveform without harmful phase shift, even when the frequency and amplitude alter simultaneously. Although active filters are typically used to compensate for the supply harmonics, where the fundamental frequency remains almost constant, we will show that our filter structure can also be applied in applications where the frequency alters rapidly     

Bulk-tuned Gm–C filter using current cancellation

A new approach for small transconductance (Gm) OTA designs, suitable for relatively low frequency filtering applications in the range of few kHz, is proposed. Small Gm values are achieved by a current cancellation technique, and are adjustable by bulk driving the MOS transistors of the input differential amplifier. The OTA design procedure takes into account Pelgrom׳s modeling of mismatch errors. A common-mode feedback control circuit based on floating gate common-mode voltage detector that shares the filter main capacitances is also presented. Experimental results obtained with a low-pass filter with tunable cutoff frequency implemented in a 0.35 μm CMOS process to verify the effectiveness of the design procedure have shown close agreement with the theory.     

一种新型可控低通滤波器的研制

针对工程地震数据采集系统中程控滤波器设计时所需控制引脚较多的弊端,研制出一种仅三线控制且品质因数Q为8的可调截止频率高速低通滤波器。通过设定开关电容滤波器MAX263可编程引脚固定的编码值,并利用分频器和高速模拟开关选取MAX263的时钟输入频率,以达到其截止频率可调的目的。测试结果表明,该滤波器对阻带信号幅度衰减稳定在–21 dB以下,且截止频率切换时延稳定在3μs以内,已成功运用于浅层数字地震仪。     

The design of 2-D nonseparable directional perfect reconstruction filter banks

In this paper, we develop a directional 2-D nonseparable filter bank that can perfectly reconstruct the downsampled subband signals. The filter bank represents two powerful image and video processing tools: directional subband decomposition and perfect reconstruction. The directional filter banks consist of (1) the input signal and the subband signals modulation, (2) diamond shape prefilter, and (3) four different parallelogram shape prefilters. This paper addresses the design and implementation of a two-band filter bank that is proved to be able to provide perfect reconstruction of the downsampled subband signals. Finally, we use a conventional 1-D half-band filter as a prototype and then apply the McClellan transform for the specific 2-D diamond shape and parallelogram shape subfilters. This method is extremely simple in designing the analysis/synthesis subfilters for the filter bank.     

基于第三代电流传输器的有源滤波器的导出

阐述了由电压模式有源RC滤波器导出基于电流传输器(CCIII)的电流模式连续时间滤波器的方法.即由运算放大器(OA)滤波器导出CC滤波器;导出的电流模式2阶滤波器结构简单,能实现2阶低通、高通、带通滤波,不仅所有无源和有源灵敏度都很低,而且当无源参数确定后,有源参数对极点频率W0不产生影响,W0保持恒定.HSPICE仿真表明,提出的电路是可行的.     

A new prefilter design for discrete multiwavelet transforms

In conventional wavelet transforms, prefiltering is not necessary due to the lowpass property of a scaling function. This is no longer true for multiwavelet transforms. A few research papers on the design of prefilters have appeared, but the existing prefilters are usually not orthogonal, which often causes problems in coding. Moreover, the condition on the prefilters was imposed based on the first-step discrete multiwavelet decomposition. We propose a new prefilter design that combines the ideas of the conventional wavelet transforms and multiwavelet transforms. The prefilters are orthogonal but nonmaximally decimated. They are derived from a very natural calculation of multiwavelet transform coefficients. In this new prefilter design, multiple step discrete multiwavelet decomposition is taken into account. Our numerical examples (by taking care of the redundant prefiltering) indicate that the energy compaction ratio with the Geronimo-Hardin-Massopust (1994) 2 wavelet transform and our new prefiltering is better than the one with Daubechies D₄ wavelet transform     

基于MOCCII多功能二阶电流模式滤波器设计

文中提出了一种基于M OCC II(多端输出第二代电流传输器)的单输入三输出二阶滤波器电路模型,由该模型可得出几种不同的滤波器电路,每种滤波器电路都由四个M OCC II、两个接地电容和电阻组成。不但能同时实现二阶高通滤波、低通滤波和带通滤波功能,还可以通过对输出端的直接组合,实现带阻和全通滤波功能及其他任意形式的二阶信号传输功能。滤波器的角频率和品质因数独立可调,应用非常灵活。与同类滤波电路相比较,该电路不但结构简单,而且使用灵活,有利于集成。同时,对其中一种滤波器的滤波特性进行了测试,实验结果表明,滤波器的滤波性能良好,电路模型完全正确。     

A low-pass notch filter for bioelectric signals

Many bioelectric signals have relatively low-frequency content, but measurement devices are susceptible to power-line interference. The Type II Chebyshev low-pass filter can simultaneously perform the required low-pass filtering and removal of the narrowband interference. This filter has transfer-function zeros which result in zero gain (- infinity dB) at specific 'null' frequencies. A procedure for the low-pass filter design makes the first null frequency a design parameter so that the notch can occur at the interference frequency.<>     

波长调制光声气体检测用锁相放大器的优化设计

首先介绍了波长调制光谱检测技术的原理,并分析了甲烷在1654 nm波长处的一次谐波频谱特性.然后分析了低通滤波器对波长调制光谱中一次谐波的影响,并给出了低通滤波器截止频率的选择范围.最后设计了模拟锁相放大器,其采用的二阶低通有源滤波器在滤波性能上比传统的RC低通滤波器有较大的提升.实验结果表明,经过优化的锁相放大器能够...     

Design and implementation of a low-pass filter for microsensor signal processing

A novel low-pass filter that consists of a switched capacitor filter(SCF) and its antialiasing prefilter and smoothing postfilter is proposed for a microsensor signal processing system,which is used in separation point detection on the surface of micro air vehicles.In the system,the filter is not only applied to finish the function of filtering but also used as the front end antialiasing filter of the over sampling analog-to-digital converter.This proposed implementation mostly relies on the design of a ...